JPH03222861A - Fuel injection system for engine - Google Patents

Abstract

PURPOSE:To regulate fuel injection time and quantity in a highly accurate manner by installing a slidable free piston whose one end fronts on a plunger chamber and the other end on the side of a return passage, respectively, in a fuel injection system with a built-in plunger to be reciprocated. CONSTITUTION:An injector 1 is fitted with a needle valve, opening or closing a nozzle 5, free of slide motion in a hole 9 of a fuel injection nozzle 2. In addition, a plunger 3 being reciprocated by a cam (unillustrated herein) interlocking with engine speed is fitted in a hole 11 on the same axis with the hole 9 free of slide motion as well, with which a plunger chamber 13 is expanded or contracted. In the midway of the hole 11, a fuel supply passage 14, a fuel injection passage 15 and a fuel return passage 16 are connected each to the specified position. In this case, a free piston 17 is slidably fitted in a hole 18 lying between the plunger 3 and the needle valve 6, and a low pressure chamber 23 being partitioned in a gap with the needle valve 6 is interconnected to the return passage 16. In this connection, downward displacement of this free piston 17 is regulated by a retainer 21.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fuel injection device for an engine that adjusts fuel injection timing and injection amount.

(Prior Art and Problems) A diesel engine has a so-called unit injector in which a fuel injection nozzle and a plunger for pumping fuel are integrally attached to a shilling head.

Conventionally, as this type of device, for example, Utility Model Application No. 61-6526
In Publication No. 9, a solenoid valve that opens and closes a return passage that returns excess fuel from the plunger chamber to the tank is interposed in the middle, and fuel injection is performed by closing this solenoid valve in the middle of the compression stroke of the plunger.

In addition, in the Vf patent publication No. 57-132 (publication No. 38), a timing plunger that makes the '0 product of the plunger chamber variable is provided in addition to the pressure-feeding plunger, and the fuel pressure that drives this timing plunger is adjusted. A solenoid valve is also provided.

In either case, the solenoid valve has to shut off the flow of high-pressure fuel at a very high speed, making it difficult to obtain sufficient timing accuracy and making it difficult to accurately adjust the fuel injection timing and amount. There was a point.

The present invention aims to solve these conventional problems.

<Means for Solving the Problems> In order to achieve the above object, the present invention includes a plunger that is reciprocated in synchronization with engine rotation, a plunger chamber that is expanded and contracted by this plunger chamber, and a feed to this plunger chamber. A fuel injection device for an engine that has a supply passage that guides pressurized fuel discharged from a pump, an injection passage that guides high-pressure fuel compressed in a plunger chamber to an injection nozzle, and a return passage that returns excess fuel from the plunger chamber to a tank. A free piston with one end facing the plunger chamber and the other end facing the return passage, which can slide, a spring that biases the free piston in the direction that the plunger chamber contracts, and a free piston with one end facing the plunger chamber and the other end facing the return passage. A means is provided to restrict the displacement of the piston in the direction in which the plunger chamber expands.

(Function) The plunger chamber is filled with fuel from the feed pump through the supply passage, and at the beginning of the compression stroke of the plunger, the 7-Lee piston slides to follow the movement of the plunger, resulting in a small pressure rise and the sliding of the plunger. After progressing to a certain degree, the sliding of the °7 Lee piston is stopped by the displacement regulating means, and the pressure in the plunger chamber is reduced! L rises sharply, and fuel is injected into the combustion chamber via the injection passage and the injection nozzle.

During the stroke in which the pressurized fuel discharged from the feed pump into the plunger chamber is illuminated, the free piston balances the fuel pressure in the plunger chamber by the biasing force of the spring.
- This causes the plunger to protrude by 7 mm during the compression stroke.
The stroke at which the Lee piston slides following the plunger is determined, and the smaller this stroke, the earlier the timing at which the pressure starts to rise in the plunger chamber, the more the fuel injection timing is advanced and the fuel injection amount is increased.

In this way, the initial stroke of the free piston changes depending on the fuel pressure introduced into the plunger chamber, making it possible to precisely adjust the fuel injection timing and injection amount.

(Example) Embodiments of the present invention will be described below with reference to the accompanying drawings.

The innoecta 1 shown in the mi diagram is attached to the cylinder head of an engine, and is provided with a fuel injection valve 7:) facing the combustion chamber, a plunger 3 for pumping fuel, and the like as a unit.

In the injection nozzle 2, a needle valve 6 for opening and closing the injection port 5 of the nozzle body 4 is slidably housed in a hole 9, and the needle valve 6 is urged in the valve opening direction by a nozzle spring 7 via a retainer 8. ing.

The plunger 3 is slidably housed in the hole 11, is urged upward by the plunger spring 12 to form a tappet 25, and reciprocates while compressing the plunger spring 12 by a cam (not shown) contacting the upper end of the tappet 25. Driven. This cam rotates in synchronization with the engine,
The piston top A has a predetermined profile for front tilt and lift.

A gloss chamber 13 that is expanded and contracted by a plunger 3 is defined within the hole 1. A fuel supply passage 14, a fuel injection passage 15, and a fuel return passage 16 are provided in the middle of the hole 11.
are connected to respective predetermined positions, fuel is fed under pressure from a feed pump (not shown) through the supply passage 14, the injected fuel is forced through the injection passage 15 to the nozzle 2, and excess fuel is sent to the tank through the return passage 1G. will be returned to.

The plunger 3 has a diagonally notched opening 10, and opens the opening of the return passage 16 during the downward movement of the plunger 3.

A free piston 17 is slidably housed in a hole 18 when the plunger 3 and the needle valve 6 are opened, and a low pressure chamber 23 defined between the free piston 17 and the needle valve 6 is connected via the return passage 16. Connects to tank.

The free piston 17 is urged upward by the spring 191, and is moved downward while compressing the spring 19 by the fuel pressure from the feed pump guided into the plunger chamber 13. The feed pump is composed of a vane pump or the like that rotates in synchronization with the engine, and has the characteristic of increasing its discharge pressure with the engine speed.

As a means for regulating the displacement of the free piston 17, a retainer 21 that comes into contact with the free piston 17 is provided.

The retainer 21 is seated on the seat surface 22 by the urging force of the nozzle spring 7.

In this embodiment, a rod portion 2 is provided at the lower end of the free piston 17.
0 protrudes, the needle valve 6 is at the m-valve position, and the 7-lea piston 17 is seated on the retainer 21. A predetermined distance between the lower end of this rod portion 20 and the upper end of the needle valve 6 is provided via the retainer 8. A gap having a value L1 is provided, and the rod portion 20 temporarily restricts the needle position. In addition, needle valve No. 7
A predetermined value L is applied to the opening of the seat surface 24 and the end face of the needle valve 6, which regulates the
A gap of 2 (L2>Ll) is provided.

I will explain the effect in detail.

Plunger chamber 13 with plunger 3 pulled up
is filled with pressurized fuel from the feed pump through the supply passage 14, and at the beginning of the compression stroke of the plunger 3, the free piston 17 slides following the movement of the plunger 3, so that the pressure no. J in the plunger chamber 13 increases. Less, plunger 3
After the sliding of the free piston 17 has progressed to a certain extent, the sliding of the free piston 17 is stopped by the retainer 21, so that the plunger chamber 1
The pressure of the needle valve 6 increases rapidly through the injection passage 15.
Fuel is injected into the combustion chamber from the nozzle 5 without lifting the engine.

During the stroke in which the plunger chamber 13 is filled with pressurized fuel discharged from the feed pump, the free piston 17 protrudes by a stroke L that balances the fuel pressure in the plunger chamber 13 due to the biasing force of the spring 19, thereby causing the compression stroke of the plunger 3. The stroke L at which the free piston 17 slides following the plunger 3 is determined, and this stroke L.

The smaller the value, the earlier the timing at which the pressure starts to rise in the plunger chamber 13, the more the fuel injection timing advances and the more the fuel injection amount increases.

Initial stroke L of the free piston 17.

varies depending on the discharge pressure of the feed pump guided into the plunger chamber 13. The discharge pressure of the feed pump increases depending on the engine speed, for example, 2 to 3 kg at low speeds.
/am? How about the stroke L of the free piston 17?
is increased to keep the fuel injection timing relatively retarded and to reduce the amount of fuel injection, for example 10K at high revolutions.
g/cta2, the stroke L of the free piston 17 is reduced, the fuel injection timing is advanced, and the injection amount is increased. In this way, the stroke L of the free piston 17 is changed by the fuel pressure introduced into the plunger chamber 13, thereby making it possible to accurately adjust the fuel injection timing and injection amount.

In this embodiment, during the compression stroke of the plunger 3, the needle valve 6
When the first 17J leap valve pressure is reached, the needle valve 6 is lifted by the clearance relative to the free piston 17, and fuel is injected from the nozzle 5 into the combustion chamber at a relatively low injection rate. When the plunger 3 continues to descend further and the pressure guided to the needle valve 6 increases and reaches the fully open valve pressure, the needle valve 6 moves to the free piston 1.
7 and the difference in pressure receiving area between the two (hole 9
is set to have a larger diameter than the hole 18), and finally rises by the gap L2, and the fuel is injected into the combustion chamber from the injection port 5 at a relatively high injection rate.

In this way, the opening pressure of the needle valve 6 is set in two stages, and the injection rate is low at the beginning of injection, which reduces the amount of ignition delay and improves fuel efficiency and smoke, and then the injection rate becomes high, resulting in short-term combustion. High efficiency and high output can be achieved.

Next, as another embodiment, as shown in FIG.
controls the opening rate of the pressure control solenoid valve 31 according to engine operating conditions such as rotational speed and load to adjust the fuel pressure guided to the plunger chamber 13.

FIG. 3 shows the characteristics of the fuel injection timing obtained by this control, and as the engine speed and load increase, the advance angle of the injection timing increases, allowing fine control of the fuel injection amount.

In addition, as shown in FIG. 4, a pressure control #33 is provided in the middle of the return passage 16 connecting the Innoecta 1 and the tank.
The control unit 34 duty-controls the opening rate of the pressure control solenoid valve 33 according to engine operating conditions such as the rotation speed and load, and adjusts the fuel pressure in the blunt chamber 13.

In this case as well, the fuel injection timing and fuel injection amount can be finely adjusted depending on the engine speed and load.

In the example shown in FIG. 5, the free piston 17
There is no provision of a part that comes into contact with the four-valve 6, and the lift of the four-well 6 is not restricted during the fuel injection stroke, so that the fuel injection rate increases and rises sharply.

(Effects of the Invention) As described above, according to the present invention, there is a blunt gloss that is reciprocated in synchronization with engine rotation, a blunt chamber that is expanded and contracted by the blunt gloss, and a pressurized fuel discharged from a feed pump into the blunt gloss chamber. In an engine fuel injection system, the end faces the plunger chamber. a free piston that is slidable with the other end facing the return passage side; a spring that biases the free piston in a direction in which the plunger chamber contracts;
Since a means is provided to restrict the displacement of the free piston in the direction in which the plunger chamber expands, the stroke of the free piston is determined according to the fuel pressure guided from the feed pump to the plunger chamber, allowing accurate fuel injection timing and injection amount. This eliminates the need for the conventional high-speed solenoid valve that connects and disconnects high-pressure fuel, reducing manufacturing costs and improving reliability.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an injector showing an embodiment of the present invention. FIG. 2 is a configuration diagram showing another embodiment, and FIG. 3 is a characteristic diagram of fuel injection timing. FIG. 4 is a configuration diagram showing still another embodiment. Figure m5 is a sectional view of an injector showing still another embodiment. DESCRIPTION OF SYMBOLS 1... Injector, 2... Nozzle, 3... Plunger 6... Side valve, 7... Nozzle spring, 13
... Plunger chamber, 14... Supply passage, 15...
・Injection passage, 16...Return passage, 17...Free piston, 19...Spring, 21...Retainer,
23...Low pressure chamber. Figure 2 Figure 3 Figure Rotation speed diagram

Claims (1)

[Claims] A plunger that is reciprocated in synchronization with engine rotation,
A plunger chamber that is expanded and contracted by this plunger, a supply passage that guides pressurized fuel discharged from the feed pump to this plunger chamber, an injection passage that guides high-pressure fuel compressed in the plunger chamber to an injection nozzle, and excess fuel from the plunger chamber. A fuel injection device for an engine is equipped with a free piston that is slidable with one end facing the plunger chamber and the other end facing the return passage, and the free piston is connected to the plunger chamber. 1. A fuel injection device for an engine, comprising a spring biased in a direction of contraction, and means for restricting displacement of a plunger chamber of a free piston in a direction of expansion.