JPH1089190A - Accumulator fuel injecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the initial injection rate in the wide injection pressure range. SOLUTION: A back pressure chamber 42 is formed on the end of a command piston separated from a needle 32, the back pressure chamber 42 is opened to a fuel pressure discharging passage 44, and the communication of the fuel pressure discharging passage 44 with the drain side is controlled by a control valve 46. A throttle B is provided on the fuel pressure discharging passage 44. An auxiliary fuel pressure discharging passage 60 is provided on the command piston 40, and a throttle C is provided on the passage 60. The back pressure chamber 42 is communicated with the drain side through the passage 44 before the command piston 40 reaches the specified lift, while, it is communicated with the drain side through the passage 60 after the command piston 40 reaches the specified lift.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure accumulating fuel injection device used for an internal combustion engine such as a diesel internal combustion engine.

[0002]

2. Description of the Related Art In a fuel injection device for a diesel engine, the noise can be reduced and the emission of nitrogen oxides (NOx) can be suppressed by keeping the initial injection rate low. For example, in Japanese Patent Publication No. Hei 4-19381, a control chamber is provided behind the needle, and a three-way valve for controlling the force generated in the control chamber in the direction of closing the needle is provided to control the injection rate characteristics as intended. ing.

In Japanese Patent Application Laid-Open No. 8-170569, a throttle is provided in a passage connecting the back pressure chamber to a fuel pressure source, so that a drop in fuel pressure from the back pressure chamber is suppressed at the beginning of injection, and the injection rate is reduced. It proposes a slow start-up.

[0004]

In the device disclosed in Japanese Patent Publication No. Hei 4-19381, the solenoid current of the three-way valve is controlled so as to obtain the desired injection rate characteristics. It will also be bulky. On the other hand, JP
In the publication No. 0569, only the release of the control pressure from the back pressure chamber is controlled by the fixed throttle, and even if the initial injection rate is reduced when the injection pressure is fixed at a certain value, the internal combustion It is difficult to obtain a characteristic of reducing the initial injection rate at all injection pressures that change depending on the operating state of the engine.

An object of the present invention is to obtain a reduction in the initial injection rate over a wide range of injection pressures.

[0006]

The present invention employs the technical means described in claim 1 to solve the above-mentioned problems. According to this technical means, the fuel discharge amount is set to the first flow rate until the command piston lift reaches the predetermined value, and the fuel discharge amount is set to the first flow rate after the command piston lift reaches the predetermined value. Flow rate adjusting means for setting the second flow rate larger than the second flow rate. Since the amount of discharge is changed according to the lift of the command piston, the two-stage injection characteristics can be obtained regardless of the operating condition. This has the effect of realizing reduction.

According to the second aspect of the present invention, the flow rate adjusting means includes a first discharge control throttle provided in the fuel pressure discharge passage and a second discharge control throttle provided in the command piston. By doing so, there is an effect that reliable two-stage injection characteristics can be obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 10 denotes a main body of a four-cylinder diesel engine, and an injector 12 is provided in a combustion chamber of each cylinder. The injector 12 of each cylinder is connected to a common rail 16 via a high-pressure pipe 14, and fuel from the common rail 16 is supplied to the injector 12 of each cylinder. The low pressure pump 18 pressurizes the fuel from the fuel tank 20 to a predetermined pressure, and the high pressure pump 22 pressurizes the fuel to a higher pressure and supplies the fuel to the common rail 16. The pressure sensor 24 detects the fuel pressure in the common rail 16 and
The detection signal is sent to the control circuit 26. Control circuit 26
Has a well-known configuration for controlling the operation of the high-pressure pump so that the pressure of the common rail 16 becomes a target value. Also,
A signal for opening and closing the injector 12 is output from the control circuit 26, and the fuel injection control is performed at an intended timing of the internal combustion engine.

In the configuration of the injector 12 shown in FIG. 2, the nozzle body 28 has a vertical hole, and a tip of the vertical hole forms a nozzle 30. The needle 32 is slidably disposed in the vertical hole, and a fuel reservoir 33 is formed in the nozzle body 28 around the needle 32. This fuel storage chamber 33 is connected to an inlet 35 from the high-pressure pipe 14 in FIG. 1 through a fuel introduction passage 34, and fuel pressure is introduced into the pressure storage chamber 33, and the fuel pressure in the fuel storage chamber 33 is controlled by the needle 32. It is biased in the valve opening direction.
On the other hand, the spring 36 urges the needle 32 to close the nozzle 30. A spacer 37 is arranged at the upper end of the nozzle body 28 and is held by a holder 38. The command piston 40 is vertically slidably fitted in the holder 38, the lower end of the command piston 40 is in contact with the upper end of the needle 32, and a back pressure chamber 42 is formed at the upper end of the command piston 40. The back pressure chamber 42 is a throttle A
Is connected to an inlet 35 from the high-pressure pipe 14 and a fuel pressure discharge passage 44 is opened. A throttle B (first discharge control throttle) is provided in the fuel pressure discharge passage 44.

The holder 3 against the command piston 40
A control valve 46 is disposed at the upper end of 8 so as to be slidable with respect to the holder 38. A drain chamber 48 is formed in the holder 38 below the control valve 46, and the control valve 46 is connected to the back pressure chamber 42 and the drain chamber 4 via a fuel pressure discharge passage 44 having a throttle B.
8 is controlled. The drain chamber 48 is connected to the fuel tank 20 of FIG.
Excess fuel is returned to the fuel tank 20. The throttle B is preferably installed to stabilize the flow characteristics of the control valve 46, but is not necessarily required.

The control valve 46 has a lower valve portion 46-1 opposed to the fuel pressure discharge passage 44, an armature 47 made of a magnetic material formed at the upper end, and a solenoid 54 wound around a magnetic material core 53. And are arranged to face. Spring 5
Numeral 6 urges the control valve 46 to move downward so that the valve portion 46-1 closes the fuel pressure discharge passage 44.
When the solenoid 54 is energized, the control valve 46 is displaced upward against the spring 56, the fuel pressure discharge passage 44 is opened, and the back pressure chamber 42 is communicated with the drain chamber 48.

In this embodiment, the control valve 46 has a vertical cylinder bore 46-2. A small-diameter balance rod 57 is slidably fitted in the cylinder bore 46-2. 58 are formed. The balance pressure chamber 58 opens at the tip of the valve portion 46-1 of the control valve 46 through a communication passage 46-3 formed through the center of the control valve 46. It is always in communication with the back pressure chamber 42 via the discharge passage 44. Note that the upper end of the balance rod 57 is supported by being in contact with a fixed portion such as the magnetic core 53, so that movement in the retreating direction is prevented.

According to the present invention, the command piston 40
Has an auxiliary fuel pressure discharge passage 60 formed therein.
One end of the passage 60 is open to the cylindrical peripheral surface of the command piston 40, and the other end is open to the back pressure chamber 42 at the upper end surface of the command piston 40. Discharge control throttle). An annular groove 62 is formed on the inner periphery of the cylindrical hole of the holder 38 on which the command piston 40 slides, and the annular groove 62 opens to the fuel pressure discharge passage 44 downstream of the throttle B via a pipe 66.

The operation of the embodiment described above will be described below. When the fuel injection is stopped, the voltage V applied to the solenoid 54 is 0 volt (FIG. 3A).
4 is demagnetized, and the fuel pressure discharge passage 44 is closed by the control valve 46 by the spring 56. Fuel from the common rail 16 is introduced into the fuel storage chamber 33 through the inlet 35 and the fuel introduction passage 34, and the fuel pressure in the fuel storage chamber 33 generates a force for lifting the needle 32. on the other hand,
Fuel pressure from the inlet 35 is introduced into the closed back pressure chamber 42. The fuel pressure in the back pressure chamber 42 is combined with the force of the spring 36 and the needle 3 through the command piston 40.
2 in the seating direction. Since the sum of the force due to the fuel pressure in the back pressure chamber 42 and the set pressure of the spring 36 is superior to the force in the lift direction due to the fuel pressure in the fuel storage chamber 33,
The needle 32 has the nozzle 30 closed, and no fuel is injected from the nozzle. In this state, the auxiliary fuel pressure discharge passage 60 is located below the annular groove 62,
Both are in a state where communication is interrupted.

The solenoid 54 is turned on to start fuel injection.
When it is charged (time t in FIG. 3)₁Voltage V = 5V),
The control valve 46 is raised by the electromagnetic attraction force, and the valve at the tip thereof
The part 46-1 is lifted from the fuel pressure discharge passage 44, and the back pressure chamber 4
2 is communicated with the drain chamber 48. Therefore, inlet 3
5 through the throttle A into the back pressure chamber 42
The charge flows out to the drain side via the throttle B. Where
The cross-sectional area of the flow _A, The cross-sectional area of the flow path of the throttle B is S_BYou
Then, S_A<S_BBecause the relationship is preset, the back pressure
The amount of fuel discharged from the back pressure chamber 42 is smaller than the amount of fuel flowing into the chamber 42.
The amount of fuel charged increases, and the pressure in the back pressure chamber increases as shown in FIG.
Starts decreasing as shown in FIG.
The force that urges the needle 32 in the valve closing direction
It gradually becomes smaller than the biasing force in the valve opening direction. So
Then t_TwoThe needle in the valve closing direction
Force that urges the needle in the valve opening direction
And the command piston rises as shown by b in (b).
The needle lifts from the valve seat
To start, the first-stage fuel injection is started. this
The injection rate at this time is indicated by c in FIG. This early
To lower the injection rate,_A≒ S_BIt is preferable to
But S_AAnd S_BIs too close to the injection period
And the emission of particulates during high-speed operation of the engine
There is a risk that the output will increase. Therefore, this
In the light period, the injection rate decreases only at the beginning of the injection,
After the initial injection period, switch to the conventional injection rate
Like that.

As shown by (b) in FIG. 3 (b), the lift of the command piston 40 in the initial injection continues and at time t ₃
When the lift amount reaches a certain value, the portion of the auxiliary fuel pressure discharge passage 60 which is opened on the peripheral surface of the command piston communicates with the annular groove 62, and the back pressure chamber 42 has the passage 60, the annular groove 62 and the passage 66. Is connected to the fuel pressure discharge passage 44 downstream of the throttle B, and the discharge speed of the fuel through the passage 60, the annular groove 62, and the passage 66 is determined by the throttle C. In the state where the auxiliary fuel pressure discharge passage 60 communicates with the annular groove 62, the amount of fuel flowing into the back pressure chamber 42 is determined by the flow area S _A of the throttle A. emissions not only the flow passage area S _B of the diaphragm B, since the amount corresponding outflow passage area of the throttle C S _C also contributes to the outflow, i.e. the diaphragm C of the flow passage area S _C is increased, the back pressure The pressure drop in the chamber 42 becomes quick as shown by a 'in FIG. 3 (c), and the lift of the command piston 40 rises as shown by b' in FIG. 3 (b). Thereby, the lift of the needle 32 is also performed rapidly, and the increase in the injection rate from the nozzle 30 is c ′.
And the second stage injection rate higher than the first stage injection rate is obtained.

At time t ₄ , the voltage applied to the solenoid 54 becomes 0 volt, the electromagnetic attraction generated in the solenoid 54 is eliminated, and the control valve 46 is lowered by the urging force of the spring 56, and its valve portion 46-1 Closes the fuel pressure discharge passage 44, the flow of fuel from the back pressure chamber 42 is stopped, and the pressure in the back pressure chamber is maintained substantially constant as indicated by a ". On the other hand, the pressure is introduced from the high pressure pipe 14 into the inlet. Since the pressure of the fuel pump is reduced, the pressure in the fuel storage chamber 33 is reduced correspondingly, the downward force applied to the command piston 40 becomes dominant, and the lift is small as shown by b ″ in FIG. And the injection rate also decreases (c ″ in FIG. 3D).

In the embodiment described above, the characteristic that the maximum injection amount is increased while suppressing the initial injection rate by utilizing the characteristic that the throttle is switched in two stages is realized. Although the term restrictor has been used in the above description, it is intended to include alternative means capable of regulating the cross-sectional area of the flow path, and may simply vary the diameter of the passage. Absent.

FIG. 4 shows an embodiment in which the injector has a plurality of nozzles 30a and 30b. Further, in order to enhance the effect of suppressing the initial injection rate according to the present invention, it is preferable to use an injector having a throttle section 80 as shown in FIG. 5 instead of the nozzle shown in FIG. The flow characteristics of the injector having such a throttle section 80 are such that the flow rate decreases at the time of low lift, so that the effect of reducing the initial injection rate according to the present invention is further enhanced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an entire system of a pressure accumulating fuel injection device for a diesel engine to which the present invention is applied.

FIG. 2 is a sectional view of an injector in the accumulator type fuel injection device of FIG.

FIG. 3 is an operation timing chart of the accumulator type fuel injection device of FIG.

FIG. 4 is a diagram showing an arrangement of nozzles in an injector.

FIG. 5 is a diagram showing another arrangement of nozzles in the injector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Diesel engine 12 ... Injector 28 ... Nozzle body 32 ... Needle 40 ... Command piston 42 ... Back pressure chamber 44 ... Fuel pressure discharge passage 46 ... Control valve 60 ... Auxiliary fuel pressure discharge passage B ... First discharge control throttle C ... Second emission control throttle

Claims (2)

[Claims] 1. A needle urged in a valve opening direction by fuel pressure, and one end is provided so as to contact the needle,
The other end is a command piston forming a back pressure chamber, a control valve provided to open and close a fuel pressure discharge passage from the back pressure chamber, and discharge of fuel from the back pressure chamber to the low pressure side when the control valve is opened. It is provided for control, and sets the fuel discharge amount to the first flow rate until the command piston lift reaches a predetermined value,
An accumulator-type fuel injection device comprising: a flow rate adjusting means for setting a fuel discharge amount to a second flow rate larger than the first flow rate after the command piston lift reaches a predetermined value. 2. The flow rate adjusting means is provided in the fuel pressure discharge passage, is provided in a first discharge control throttle connecting a back pressure chamber to a drain side, and in a command piston, and the command piston reaches a predetermined lift. 2. The accumulator type fuel injection device according to claim 1, further comprising a second discharge control throttle connecting the back pressure chamber to the drain side.