JPH0658217A - Fuel injection device for diesel engine - Google Patents

Abstract

PURPOSE:To enable pilot injection and main injection to be conducted by controlling pressure in a first control chamber and a second control chamber with one operation of a control valve while using instantaneous fuel leak from high pressure side to low pressure side. CONSTITUTION:There are provided an accumulation lining 26 in which high pressure fuel is accumulated and a slidably arranged nozzle needle 5 for opening and closing an injection port 4 communicated with the accumulation lining 26. A first control chamber 16 keeps a pressure for closing the nozzle needle 5. A second control chamber 17 keeps a pressure for opening the nozzle needle 5. A control valve 116 changes inflow of fuel from the accumulation lining 26 to the first control chamber 16, over outflow of the fuel from the first control chamber 16 to the second control chamber 17. A throttle valve means 63 controls outflow of the fuel from the first control chamber 16 to a low pressure side. Pilot injection is enabled by one operation of the control valve, through introduction of instantaneous fuel leak to a low pressure chamber.

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 a diesel engine.

[0002]

2. Description of the Related Art Conventionally, as a fuel injection device for a diesel engine, there is one disclosed in JP-A-59-165858. This is composed of a common accumulator pipe called a common rail for accumulating high-pressure fuel and an injector for injecting fuel. A nozzle needle for opening and closing the injection hole is slidably arranged in this injector, and
A control chamber that holds the fuel pressure that acts on this nozzle needle is formed, and the pressure in this control chamber is controlled by the three-way solenoid valve to switch between high-pressure side fuel pressure and low-pressure side fuel pressure. The high-pressure fuel supplied from the pipe is injected from the injection hole.

The movement of the nozzle needle that opens and closes the nozzle hole is
The pressure in the control room is dominated by switching from high pressure to low pressure or from low pressure to high pressure.

[0004]

However, in such a conventional fuel injection device for a diesel engine,
Since a highly responsive solenoid valve capable of switching from high pressure to low pressure twice in the control chamber in a short time during pilot injection is required, the electric energy consumption required to operate the solenoid valve twice is required. There is a problem that it becomes excessive and the cost of the electronic control device for operating such a solenoid valve twice becomes high.

The present invention has been made in order to solve such a problem, and devises the structure of the injector to introduce a momentary fuel leak from the valve means into the low pressure chamber when the solenoid valve is operated. Therefore, an object of the present invention is to provide a fuel injection device for a diesel engine that enables pilot injection by operating the solenoid valve once.

[0006]

A fuel injection device for a diesel engine according to the present invention comprises a pressure accumulating pipe for storing high pressure fuel, and a slidably arranged nozzle needle for opening and closing a nozzle hole communicating with the pressure accumulating pipe. A first control chamber that holds a pressure for closing the nozzle needle, a second control chamber that holds a pressure for opening the nozzle needle, and a fuel from the pressure accumulation pipe to the first control chamber Control valve for switching the inflow of the fuel and the outflow of the fuel from the first control chamber to the low pressure side and the second control chamber, and a throttle means for limiting the outflow of the fuel from the first control chamber to the low pressure side. It is characterized by having.

[0007]

According to the fuel injection device for a diesel engine of the present invention, since the low pressure side of the control valve is closed during non-injection, the high pressure is maintained in the first control chamber. When the control valve is turned on at the start of pilot injection, the pressure in the first control chamber gradually decreases, and the instantaneous leak fuel generated from the control valve is introduced into the second control chamber through the leak passage. At this time, the pressure in the second control chamber is increased by the throttle means, the nozzle needle is lifted, and pilot injection is started.

When the control valve is completely seated at the end of pilot injection, the instantaneous fuel leak disappears, and the second
The fuel in the control chamber is discharged through the throttle means, the pressure is reduced, the nozzle needle is seated, and the pilot injection ends. At the start of the main injection, the pressure in the first control chamber gradually decreases due to the fuel outflow through the throttle means at the same time as the operation of the control valve, and eventually the nozzle needle starts to rise and the main injection starts.

When the control valve is turned off at the end of the main injection, the pressure in the first control chamber rises and the nozzle needle descends to sit down and finish the main injection. Immediately after the control valve is turned off, a momentary fuel leak occurs in the leak passage, and the pressure in the second control chamber rises due to the same operation as described above. Since the sudden lowering is alleviated, the impact load when the nozzle needle is seated is reduced.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, the casing member 1 of the injector 100 includes a first body lower 1a and a second body lower 1a.
b, a connecting portion 1c, and a valve casing 1d, members 1a and 1b are integrally connected by a first retaining ring 1e, and respective members 1b, 1c, 1d are integrally connected by a second retaining ring 1f. Has been done. A valve body sliding hole 2 and a fuel storage chamber 3 are formed in the valve casing 1d, and a large diameter portion 6 of a nozzle needle 5 is slidable in the valve body sliding hole 2 communicating with the fuel storage chamber 3. It is fitted. A connecting portion 7 is formed on the large diameter portion 6 of the nozzle needle 5, and a small diameter portion 8 and a valve body portion 9 are integrally formed further downward. Then, the injection hole 4 of the seat portion x is opened and closed by the valve body portion 9. A piston pin 11 is connected to the tip of the connecting portion 7 of the nozzle needle 5 via a flange 10.

The first piston 12 is slidably fitted in a cylinder 14 formed in the first body lower 1a, and a first control chamber 16 is formed above the first piston 12. . When the pressure of the fuel in the first control chamber 16 rises, the nozzle needle 5 descends. The passage 36 shown in FIG.
A one-way orifice is provided between this and the first control chamber 16. The nozzle needle 5 is biased in the closing direction by the compression coil spring 13.

The second piston 15 is the first piston 1
2 is integrally formed with the second piston 12, and is slidably provided in a cylinder 18 having a larger diameter than the outer diameter of the first piston 12 and a larger inner diameter than the cylinder 14. Further, a second control chamber 17 is formed below the second piston 15. When the fuel pressure in the second control chamber 17 rises, the nozzle needle 5 rises. That is, the direction of the force acting on the nozzle needle 5 when the pressure of the fuel in the chamber is increased is opposite to that in the case of the first control chamber 16.

A three-way solenoid valve 116 is provided above the first piston 12. That is, as shown in FIG. 3, the outer valve 118 is slidably fitted in the inner hole 117a of the cylinder body 117.
An inner valve 119 is provided in each of the inner holes 118a of the eighteen. The outer seat 40 formed on the cylinder body 117 is a valve seat portion for the outer valve 118 to come into contact with and separate from, and an inner seat 42 formed on the outer valve 118.
Is a valve seat portion with which the inner valve 119 contacts and separates. A movable iron core 43 is fixed to the outer peripheral wall above the outer valve 118.

As shown in FIG. 1, a stator 47 for fixing the coil 20 is housed in a solenoid housing 48, and this solenoid housing 48 is fitted in a cylindrical case 50 via an O-ring 49. . A terminal 51 for connecting a lead wire that is electrically connected to the coil 20 is provided on the upper portion of the case 50, and a connector 52 for fixing the terminal 51 is caulked and fixed by a caulking portion 48. A compression coil spring 21 is provided on the upper end of the outer valve 118.

When the coil 20 is demagnetized, the movable iron core 43 is in the lowered position and the outer valve 118 is in the lower position by the urging force of the compression coil spring 21, as shown in FIG. As a result, the high pressure fuel passage 2
2 and the first control room 16 are the groove 32, the inner seat 4
2, communication is established via the internal hole 58 and the passage 36. In a transitional state in which the coil 20 switches from the demagnetized state to the excited state or from the excited state to the demagnetized state, the outer valve 118 moves upward from the position shown in FIG. 3, the outer valve 118 separates from the outer seat 40, and the inner valve 119 also Separated from the inner sheet 42. As a result, the high-pressure fuel passage 22 is in communication with the drain passage 23 via the groove 32, the inner seat 42, the inner hole 58, the passage 36, and the outer seat 40.
When the coil 20 is excited, the outer valve 118
Is in the upwardly moved position shown in FIG. This allows
The inner seat 42 is closed, the outer seat 40 is opened, and the first control chamber 16 is in communication with the drain passage 23 through the passage 36 and the inner seat 40.

As shown in FIG. 1, the drain passage 23 communicates with a leak passage 60, and the leak passage 60 communicates with the second control chamber 17 via a groove 61. Further, the leak passage 60 has a drain passage 62 through an orifice 63.
Is in communication with. The drain passage 62 communicates with a spring chamber 64 in which the compression coil spring 13 is provided. The spring chamber 64 communicates with the drain passages 65 and 66 as shown in FIG. 2, one end of the drain passage 66 communicates with the cylinder 18 on the back side of the second piston 15, and the other end communicates with the outlet 68. is doing.

A fuel supply passage 24 is formed in the casing member 1, and one end of the fuel supply passage 24 has a fuel reservoir 3
And the other end is connected to the high-pressure fuel passage 22 of the three-way solenoid valve 116. The pressure accumulating pipe 26 accumulates the high pressure fuel supplied from a high pressure supply pump (not shown), and the pressure accumulating pipe 26 supplies the high pressure fuel to the injector 100 provided for each cylinder via the inlet 25. The controller 28 is a cylinder discrimination sensor,
The signals from the cam angle sensor and the accelerator opening sensor are input to the three-way solenoid valve 16 at a predetermined fuel injection timing.
To control.

Next, the operation will be described. Accumulation pipe 2
The high-pressure fuel 6 is supplied into the injector 100 via the inlet 25. This fuel is supplied to the fuel storage chamber 3 via the passage 24 and also to the three-way solenoid valve 116. When the three-way solenoid valve 116 is demagnetized, the outer valve 118 is seated on the outer seat 40 by the compression coil spring 21, and as shown in FIG. 3, high pressure fuel flows from the high pressure fuel passage 22 to the groove 32 and the through hole 56. , Through the inner hole 18a, the inner sheet 42, and the inner hole 58 into the passage 36. As a result, the nozzle needle 5 maintains the valve closed state.

When the three-way solenoid valve 116 is excited, the outer valve 118 is sucked upward from the position shown in FIG. 3 to the position shown in FIG. 4, and the high pressure fuel in the first control chamber 16 and the passage 36 is stored in the outer seat 40. Leak passage 2 through the surroundings
It is flowed to the low pressure side via 3, 60. When the high pressure in the first control chamber 16 is made to flow to the low pressure side, the piston 12 shown in FIG. 1 rises to a predetermined stopper contact position, and fuel injection is thereby started. Then, the outer valve 118 is changed to the one shown in FIG.
5 further rises to the position shown in FIG. 5, and the inner valve 119 is seated on the inner seat 42. At this time, the nozzle needle is in the full lift state, and the injection rate reaches the maximum timing.

Then, when the three-way solenoid valve 116 is demagnetized, the outer valve 118 is seated on the outer seat 40 in the closed position downward due to the urging force of the compression coil spring 21. When the outer valve 118 is seated on the outer seat 40, the flow of fuel from the passage 36 to the leak passage 23 is stopped, and the high pressure fuel passes around the inner seat 42 and passes through the inner hole 58 to pass through the first control from the passage 36. Chamber 16
And ends the fuel injection.

Next, how the injection rate of the injector 100 changes due to the change in the drive current of the three-way solenoid valve 116 will be described with reference to FIG. In FIG. 6, the solenoid valve pulse indicates a pulse applied to the three-way solenoid valve 116, the valve lift indicates the lift amount of the outer valve 118, the instantaneous leak amount indicates the fuel leak amount escaping from the passage 36 to the drain passage 23, 1 control chamber pressure and 2nd
The control chamber pressure indicates the pressure in each control chamber 16 and 17, the needle lift indicates the lift amount of the nozzle needle 5, and the injection rate indicates the injection rate of the injector 100.

Where P ₁ is the pressure acting on the first control chamber 16, P _{2 is} the pressure acting on the fuel storage chamber 3, and P _{3 is} the second pressure.
Pressure acting on control chamber 17, A ₁ : first piston 12
Pressure receiving area of A ₂ , A ₂ : pressure receiving area of nozzle needle 5, A _2
3 : The pressure receiving area of the second piston 15, F _S : the biasing force of the compression coil spring 13. When not injecting, the nozzle sheet is established by the following formula.

P ₁ × A ₁ + F _S ≧ P ₂ × A ₂ − At the start of pilot injection, when the three-way solenoid valve 116 is turned on and the outer valve 118 is sucked, a momentary leak occurs and the second leak from the leak passage 60 occurs. Leak fuel is introduced into the control chamber 17. At this time, the orifice 63 restricts the second
The pressure in the control chamber 17 rises, the nozzle needle 5 lifts according to the following equation, and pilot injection starts.

P ₁ ′ × A ₁ + F _S ≦ P ₂ × A ₂ + P ₃ × A ₃ − At the end of pilot injection, when the outer valve 118 is completely sucked and the seat is established, the fuel leak disappears and the second control chamber 17 The fuel is discharged through the orifice 63 and the pressure drops, and the pilot injection is completed by the following equation. P ₁ ″ × A ₁ + F _S ≧ P ₂ × A ₂ − Then, at the start of the main injection, the pressure in the first control chamber 16 gradually decreases due to the fuel outflow through the orifice simultaneously with the operation of the three-way solenoid valve 116. Eventually, the nozzle needle 5 starts to rise according to the following equation, and the main injection starts.

P ₁ ′ ″ × A ₁ + F _S ≦ P ₂ × A ₂ − When the three-way solenoid valve 116 is demagnetized at the end of the main injection,
The pressure in the first control chamber 16 rises and the nozzle needle 5 descends. On the other hand, a momentary fuel leak occurs in the leak passage 60, and the pressure in the second control chamber 17 rises due to the same operation as described above. Therefore, since the descending speed of the first piston 12 due to the high-pressure fuel flowing into the first control chamber 16 is reduced by the upward force of the second piston 15, the impact load when the nozzle needle 5 is seated can be reduced.

According to the above-described embodiment, in the process of shifting from the non-injection state to the pilot injection and then to the main injection, as shown in FIG. 6, the first control chamber 16 and the second control chamber 1
By appropriately changing the pressure behavior of No. 7, pilot injection and main injection can be performed simultaneously by one drive current. Furthermore, at the end of the main injection, the second control chamber 1
As the pressure of 7 increases, the descending speed of the nozzle needle 5 decreases immediately before seating, so that the wear of the seat portion is reduced and the reliability of the injector is enhanced. Further, since the nozzle suck volume of the valve seat x can be reduced by reducing the wear immediately before seating, there is an effect that the generation amount of unburned harmful exhaust gas such as HC can be reduced by preventing the fuel dripping.

[0027]

As described above, according to the fuel injection device for a diesel engine of the present invention, when the fuel pressure of the nozzle needle exhaust pressure chamber (first control chamber) is switched to the high pressure side or the low pressure side by the solenoid valve. The instantaneous fuel leak from the high pressure side to the low pressure side is used to control the pressures of the first control chamber and the second control chamber by a single solenoid valve operation, thereby enabling pilot injection and main injection. Therefore, it is possible to reduce the amount of electrical energy consumed to energize the solenoid valve. Further, since the control by the electronic control device can be simplified, there is an effect that the pilot injection and the main injection can be performed by the low-cost electronic control device.

[Brief description of drawings]

FIG. 1 is a sectional view showing a fuel injection device for a diesel engine according to an embodiment of the present invention.

2 is a cross-sectional view showing a fuel injection device for a diesel engine according to an embodiment of the present invention, taken along a section different from that in FIG.

3 is a cross-sectional view for explaining the behavior of the three-way solenoid valve shown in FIG.

4 is a cross-sectional view for explaining the behavior of the three-way solenoid valve shown in FIG.

5 is a cross-sectional view for explaining the behavior of the three-way solenoid valve shown in FIG.

FIG. 6 is a time chart diagram of a fuel injection device for a diesel engine according to an embodiment of the present invention.

[Explanation of symbols]

 4 Nozzle 5 Nozzle Needle 12 First Piston 15 Second Piston 16 First Control Chamber 17 Second Control Chamber 20 Coil (Electromagnetic Coil) 21 Compression Coil Spring 22 High Pressure Fuel Passage 23, 60 Leakage Passage 26 Accumulation Piping 30 Cylinder Body (control valve) 40 Outer seat 42 Inner seat 62, 65 Drain passage 63 Orifice (throttle means) 100 Injector 116 Three-way solenoid valve (control valve) 118 Outer valve (control valve) 119 Inner valve (control valve)

Claims (1)

[Claims] 1. A pressure accumulating pipe for storing high-pressure fuel, a slidably arranged nozzle needle for opening and closing an injection hole communicating with the pressure accumulating pipe, and a first pressure holding member for closing the nozzle needle. A control chamber, a second control chamber for holding a pressure for opening the nozzle needle, an inflow of fuel from the pressure accumulating pipe to the first control chamber, and a low pressure side and a second side from the first control chamber. A fuel injection device for a diesel engine, comprising: a control valve that switches between outflow of fuel to a control chamber and throttle means that restricts outflow of fuel from the first control chamber to the low pressure side.