JPH0436261B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel injection control device for a unit injector used in a diesel engine.

Diesel engines use fuel injection to
Normally, it is equipped with an injection pump that increases the pressure of the fuel, a fuel injection pipe that supplies the fuel pumped from the injection pump to the nozzle, and a nozzle that injects the high-pressure fuel. There is an injector. This unit injector eliminates the need for a long fuel injection tube, so the injection delay is small, and the volume to be compressed is reduced by the lack of a fuel injection tube, resulting in high injection pressure and atomization of the fuel. In addition to advantages such as good fuel efficiency, it also has other advantages such as being able to increase the injection rate and reducing the amount of fuel left behind at the end of injection.

A fuel injection system in which such a unit injector is disposed in each cylinder has been proposed, for example, in Japanese Patent Laid-Open No. 56-50726 (U.S. Pat. No. 4,129,253), and this is shown in FIGS. 1 and 2. Shown below.

1 and 2, a plunger 4a is slidably inserted into a cylinder 3 bored in the main body 2 of the unit injector 1, and this plunger 4a is connected to a plunger 4b. The plunger 4b is biased upward in the figure by a spring 6 interposed between its head and the main body 2, and a cam (not shown) that rotates in synchronization with the engine is attached to the head upward. Since the plunger 4b is pressed down every rotation of the cam, the plunger 4a connected to the plunger 4b reciprocates up and down.

The pressure chamber 7 of the cylinder 3, which is formed facing one end of the plunger 4a, communicates with a fuel tank (not shown) via fuel supply passages 8a, 8b, and a low-pressure fuel supply pump ( (not shown) supplies fuel in the fuel tank to the pressure chamber 7.

A nozzle 10 is formed in the lower part of the main body 2 to inject fuel in the pressure chamber 7 pressurized by the descent of the plunger 4a into a combustion chamber (not shown). Specifically, the nozzle 10 includes a needle chamber 11, a needle valve 12, a spring 13, a nozzle hole 14, a spring guide 15, and a spring chamber 16, which communicate with the pressure chamber 7 via a fuel passage 9.
Normally, the spring 13 urges the needle valve 12 downward via the spring guide 15 to close the nozzle hole 14, but the fuel in the pressure chamber 7 is sent to the needle chamber 11 via the fuel passage 9, and this When the fuel pressure in the needle chamber 11 overcomes the spring 13,
The needle valve 12 is urged upward to open the nozzle hole 14, and the fuel in the needle chamber 11 is injected from the nozzle hole 14. Therefore, spring 1
3 sets the valve opening pressure of the nozzle 10.

A solenoid valve 18 as a valve device is interposed in the fuel supply passages 8a and 8b communicating with the pressure chamber 7. In the solenoid valve 18, a valve body 21 that slides on a cylinder 20 bored in a valve holder 19 is biased by a spring 22 to open the solenoid valve 18. When a driving current is applied to the solenoid 24, the solenoid 24 The armature 26 is configured to urge the valve body 21 in the valve closing direction against the spring 22 by electromagnetic force to seat it.

When the solenoid valve 18 is opened, the fuel in the pressure chamber 7, which becomes high pressure due to the descent of the plunger 4a, flows through the solenoid valve 18.
However, the orifice 17 regulates the fuel flow rate at this time to keep the fuel pressure in the pressure chamber 7 and the passages 8b and 9 at a predetermined value lower than the opening pressure of the nozzle 10. That's what I do.

A control circuit (not shown) that controls the drive current to the solenoid valve 18 includes means for detecting the operating state of the engine (for example, an engine rotation speed sensor, an accelerator sensor that detects the depression angle of the accelerator pedal, and a sensor that detects the cooling water temperature of the engine). Based on the detection signal from the water temperature sensor, crank angle sensor that detects the crank angle, etc.
A signal having a drive pulse width optimal for the engine operating condition is output to the solenoid 24 to control the opening and closing of the solenoid valve 18.

A fuel relief passage 28 communicating with the spring chamber 16
After merging, the fuel relief passage 28b communicating with the annular groove 29 formed in the upper part of the cylinder communicates with the fuel supply passage 8a upstream of the electromagnetic valve 18, and returns excess fuel to the passage 8a.

Therefore, the fuel in the fuel tank pre-pressurized by the fuel supply pump is transferred from the fuel supply passage 8a to the solenoid valve 1.
When the fuel is supplied to the pressure chamber 7 via the valve 8 (open), the plunger 4a is lowered by a cam that rotates in synchronization with the engine and begins to pressurize the fuel in the pressure chamber 7. At this point, however, the electromagnetic Since the valve 18 is open, a part of the pressurized fuel escapes through the solenoid valve 18, and the fuel flow rate is regulated by the orifice 17, so that the fuel pressure in the pressure chamber 7 and passages 8a and 9 does not exceed a predetermined value. Not reached.

When the solenoid 24 is energized and the electromagnetic valve 18 is closed during the descent of the plunger 4a, the fuel in the pressure chamber 7 is trapped and the fuel pressure increases, and this fuel pressure reaches the needle chamber 11 via the fuel passage 9. When the fuel pressure in the needle chamber 11 overcomes the downward urging force of the spring 13 (valve opening pressure of the nozzle 10), the needle valve 12 is pushed upward and the nozzle hole 14 is opened.
Fuel in the needle chamber 11 is injected into a combustion chamber (not shown).

When the solenoid 24 is de-energized at a predetermined crank angle and the solenoid valve 18 is opened, part of the fuel in the pressure chamber 7 escapes to the fuel supply passage 8a via the solenoid valve 18 as described above, so that the needle chamber The fuel pressure at No. 11 quickly decreases to below the opening pressure of the nozzle 10, and the injection ends.

In other words, fuel injection is performed while the solenoid valve 18 is closed.
By changing the timing and duration of energization to the solenoid 24, which opens and closes, depending on the operating state, the injection timing and amount of fuel injected from the nozzle 10 can be optimally controlled.

By the way, the maximum lift amount of the solenoid valve 18 is uniquely determined by the gap amount between the armature and the core, and the lift of the valve body 21 of the solenoid valve 18 forms between the valve body 21 and the valve seat. The area of the leak orifice is limited by this maximum lift amount, so if the maximum lift amount is small, the drop in injection pressure at the end of injection is slow, resulting in poor injection quality.

Therefore, in order to increase the leak orifice area, it is possible to increase the seat diameter of the valve body or to increase the maximum lift amount of the valve body. In the former case where the seat diameter is increased, the electromagnetic force for seating the valve body must also increase in accordance with the increase in the seat diameter.
For example, if the injection pressure is about 1000 atm,
Even if the seat diameter is as small as 2 mm, a force of at least 30 kg is required to seat the seat.

On the other hand, in the latter case where the maximum lift amount of the valve body is increased, the attracting electromagnetic force is inversely proportional to the square of the gap amount, so if the maximum lift amount is increased, the electromagnetic force must be increased in proportion to the square of the lift amount. Must be.

In either case, in order to increase the driving electromagnetic force, the solenoid valve must be made larger, and when considering application to small high-speed engines, the solenoid valve is required to have quick response, which is not possible. The solenoid valve that does this ends up being large or expensive.

Therefore, the same inventor as the present inventor has devised a device that increases the seat diameter without increasing the driving electromagnetic force and improves the sharpness of fuel injection by increasing the leak orifice area.

It has a cylinder facing the back of the valve body,
In this cylinder, a piston having a diameter almost the same as the seat diameter of the valve body head is provided integrally with the valve body so that this piston slides, and a back pressure chamber defined by the cylinder and the piston and a seat A pressure balance passage that communicates with a fuel supply passage upstream of the valve body passes through the valve body at its axial center.

In this way, the valve opening force due to high fuel pressure acting on the valve body head and the valve closing force due to the same fuel pressure acting on the valve body back are balanced, and the influence of fuel pressure on valve body drive can be removed. The driving electromagnetic force only needs to be relatively small, and in the case of such a solenoid valve, even if the seat diameter is increased again, the electromagnetic force is not affected much.

Therefore, the seat diameter can be increased without increasing the electromagnetic force, and as the seat diameter increases, the leak orifice area expands, the injection pressure rapidly decreases, and the injection becomes better.

By the way, FIG. 6A shows a streamline distribution drawn in the state of such a solenoid valve in the middle of opening lift (details will be described later).

That is, the valve body 43 is lifted to the right,
The high pressure fuel from the pressure chamber 7 is divided into two parts at the head of the valve body 43. One way is to escape to the fuel supply passage 8a through the leak orifice between the valve body 43 and the valve seat 59, and the other way is to go through the pressure balance passage 73 to the back pressure chamber, but the back pressure chamber is closed. Because it is a confined space, the fuel remains confined.

Therefore, in the passage 55 upstream of the seat portion, the streamlines that coincide with the flow velocity direction of the fuel have a distribution that swells toward the center of the passage, and when fuel having such a streamline distribution flows to the head of the valve body 43, this The distribution of the pressure P acting on the head of the valve body 43 at this time is highest near the axis C of the valve body 43, as shown in FIG. 6B.

The fuel pressure acting near the axis C of the valve body 43 is generally high, but since the pressure balance passage 73 passes through the axis C of the valve body 43, the high fuel pressure near this axis C is caused by the pressure balance passage. 73 and reaches the back pressure chamber, this high fuel pressure acts on the valve body 43 in the valve closing direction (to the left), while the fuel pressure acting on the valve body 43 in the valve opening direction (to the right) The fuel pressure is relatively low in a portion that is more than the opening radius of the pressure balance passage 43 than C.

That is, when the valve body 43 is opened and lifted, the valve body 4
The fuel pressure acting in the valve opening direction of valve element 43 becomes lower than the fuel pressure acting in the valve closing direction of valve element 43, causing an imbalance of pressure between the head and back of valve element 43. Since the valve element driving force corresponding to this fuel pressure difference acts in a direction that prevents the valve element 43 from opening and lifting, the dynamic characteristics of the solenoid valve become unstable.

A good countermeasure against this problem is to increase the setting load of the elastic member (spring) that biases the valve body 43 in the valve closing direction, but if the setting load is increased, the driving electromagnetic force must be increased accordingly. However, if this happens, there is a fear that the original purpose of increasing the seat diameter without increasing the electromagnetic force will be violated.

Therefore, an object of the present invention is to stabilize the dynamic characteristics of a solenoid valve while maintaining the current driving electromagnetic force.

For this reason, in the present invention, a piston that slides on a cylinder facing the back of the valve body of the valve device is provided integrally with the valve body, and a back pressure chamber defined by the cylinder and the piston is formed by a pressure balance passage. In addition to the above-mentioned fuel injection control device which includes a configuration that communicates with the fuel supply passage upstream of the seat portion through the fuel injection control device, the following items are additionally provided.

In other words, a flow guide is provided in the fuel supply passage upstream of the seat part at a position facing away from the opening of the pressure balance passage, and when the valve body is opened and lifted, the fuel pressure near the maximum due to the relief fuel flowing around the flow guide is maintained. acts on the head of the valve body outside the opening to regulate the flow of relief fuel.

In this way, near maximum fuel pressure acts on the valve head in the valve opening direction, while relatively low fuel pressure reaches the back pressure chamber via the pressure balance passage, and this pressure is applied to the valve body. Therefore, the valve element driving force corresponding to these fuel pressure differences acts in a direction that assists the valve opening lift of the valve element 43.

The following description will be made based on the illustrated embodiments.

FIG. 3 is a schematic configuration diagram of the first embodiment of the present invention,
Reference numeral 4 denotes a plunger that integrates the two plungers 4a and 4b shown in FIGS. 1 and 2, 30 a cam that rotates in synchronization with the engine, 31 a pin for preventing the plunger 4 from coming off, 32 a support, and 33 a holder; 34 is a nozzle holder; 35 is a distance piece that regulates the lift amount of the needle valve 12; 36 is a nozzle nut that fixes the nozzle holder 34 and the distance piece 35 to the holder 33; 38 is a fuel relief passage to the fuel tank; 39 is a shim that adjusts the valve opening pressure of the nozzle 10.

Reference numeral 40 designates a solenoid valve as a valve device installed in the fuel supply passages 8a, 8b, and an enlarged sectional view thereof is shown in FIG.

In the figure, a needle-shaped valve body (needle valve) 43 is slidably fitted into a cylinder 42 formed in a valve holder 41, and inside a case 44 of the valve holder 41, screws 45 are installed around the upper end of the valve body 43. An armature 46 is fixed via a shim 58 at the armature 46, a core 47 that attracts the armature 46, a solenoid 48 that excites the core 47, a terminal 49 to which a control signal is supplied to the solenoid 48, and a valve body 43 via a stopper 50. A spring 51 is housed therein, which urges it upward in the figure.

A valve chamber 52 formed facing the head of the valve body 43 (lower end of the valve body) communicates with the fuel supply passage 8a via a passage 53 and the chamber 52, and communicates with the fuel supply passage 8b via a passage 55. ing.

Therefore, the armature 46 is normally separated from the core 47 due to the upward biasing force of the spring 51, and the valve body 43 is separated from the valve seat 59 formed in the valve holder 41 (opens), and the valve body 43 is separated from the valve seat 59 formed in the valve holder 41 and connected to the fuel supply passage 8a. When the solenoid 48 is energized from a control circuit (not shown) at a predetermined crank angle, the core 47 is excited and attracts the armature 46, and the valve body 43 is seated on the valve seat 59. (the valve will be closed).

The upper part of FIG. 5 shows the applied voltage applied to the solenoid 45 of such a solenoid valve 40 and the lift characteristics.

That is, when the solenoid valve 40 is energized for a period from T ₁ to T ₃ , the solenoid valve 40 is closed for a period from T ₂ to T ₄ with a response delay.

Returning to FIG. 4, a cylinder 70 is provided facing the back of the valve body (upper part of the valve body), and a piston 71 that is slidably fitted into the cylinder 70 is integrally formed on the back of the valve body 43.

The back pressure chamber 72 and the passage 55 are centered on the axis of the valve body 43 so that the fuel pressure upstream of the seat portion of the valve body 43 and the valve seat 59 is guided to the back pressure chamber 72 defined by the cylinder 70 and the piston 71. It passes through a pressure balance passage 73 that communicates with the.

Therefore, the fuel pressure upstream of the seat portion acting on the head of the valve body 43 and the fuel pressure in the back pressure chamber 72 acting on the back of the valve body 43 are approximately equal.

Here, since the force acting on the valve body is determined by the fuel pressure and the pressure receiving area on which this fuel pressure acts, the valve opening is determined by the fuel pressure upstream of the seat part of the head of the valve body 43 and the pressure receiving area of the seat part. The diameter of the piston 71 is set so that the force and the valve closing force determined by the fuel pressure in the back pressure chamber 72 at the back of the valve body 43 and the pressure receiving area of the piston 71 are approximately balanced.

The present invention further provides an orifice 80 at the opening of the pressure balance passage 73 at the head of the valve body 43 to reduce the opening area to the pressure balance passage 73.

On the other hand, a flow guide 8 that faces the orifice 80 and has an outer diameter larger than the orifice diameter is disposed in the passage 55 immediately upstream of the seat portion of the head of the valve body 43.
1 are spaced apart from each other.
2 is held between the holder 33 and the valve holder 41, and a communication hole 83 is bored in the flange portion 82.

However, the annular passage 55 surrounding the flow guide 81 is designed to ensure a sufficient fuel flow rate.
The outer diameter of the flow guide 81 is set so that the area 5 is at least four times larger than the area of the leak orifice formed between the valve body 43 and the valve seat 59.

Reference numeral 56 on the upper part of the case 44 is a stopper for fixing the cylinder 70, and reference numeral 57 is a stopper lock for fixing the stopper 56 by screwing it.

Also, 60 is a fuel relief passage, group 61,
It communicates with an armature chamber 65 via a passage 62, a spring chamber 63, and a passage 64, and is configured to return excess fuel to the fuel tank. 66 is a seal ring.

Other components are the same as in Figures 1 and 2,
Identical components are given the same reference numerals and their explanations will be omitted.

The effect of the above configuration will be explained.

Fuel in the fuel tank pre-pressurized by the fuel pump is supplied to the pressure chamber 7 from the fuel supply passage 8a via the chamber 54, the passage 53, the leak orifice, and the passage 55.

When the plunger 4 is lowered by the cam 30 rotating in synchronization with the engine and begins to pressurize the fuel in the pressure chamber 7, the fuel pressure is increased in the reverse order of the fuel supply described above, that is, from the fuel supply passage 8b to the passage 55, The fuel pressure escapes to the fuel supply passage 8a via the leak orifice, the passage 53, and the chamber 54, and since the flow guide 81 and the opening of the orifice 80 are separated, the fuel pressure passes through the orifice 80 and the pressure balance passage 73 to the back pressure chamber. It reaches 72.

The fuel pressure upstream of the seat part of the head of the valve body 43 and the
The piston diameter is set so that the fuel pressures in the back pressure chamber 72 at the back of the valve body 3 are approximately equal, and the pressure receiving areas on which these fuel pressures act are also approximately equal at the head of the valve body 43 and at the back of the valve body 43. Since the valve opening force acting on the head of the valve body 43 and the valve closing force acting on the back of the valve body 43 cancel each other out, the valve body 43 is separated from the valve seat 59 only by the upward biasing force of the spring 51 in the figure. .

That is, while the fuel pressure from the pressure chamber 7 is low,
Since the fuel pressure is balanced between the head and back of the valve body 43, the electromagnetic force that drives the valve body 43 of the solenoid valve 40 in the valve closing direction depends on the weight of the valve body 43, the armature 46, etc., and the viscosity of the fuel. It only needs to be able to resist the opposing force, and even a relatively small electromagnetic force can drive the opening and closing regardless of high-pressure fuel.

Therefore, even if the seat diameter is increased, the drive electromagnetic force can be kept relatively small, and in this embodiment, the seat diameter is set large.

Therefore, when the solenoid 48 is energized while the plunger 4 is descending, the valve body 43 is moved down by a small electromagnetic force and seats on the valve seat 59 (closed).

Since communication between the fuel supply passages 8a and 8b is cut off by this valve closing, the fuel in the pressure chamber 7 is trapped and the fuel pressure is increased. This fuel pressure reaches the needle chamber 11 via the fuel passage 9, increases the pressure (injection pressure) in the needle chamber 11, and when it exceeds the valve opening pressure of the nozzle 10, the needle valve 12 lifts upward, and the injection hole 14 Fuel is injected, and thereafter the injection pressure increases as the fuel pressure in the pressure chamber 7 increases.

When the voltage application to the solenoid 48 is finished at a predetermined crank angle, the valve body 43 starts to lift in the valve opening direction, but the outer diameter of the flow guard 81 is larger than the orifice 8.
Since the opening diameter is set larger than the opening diameter of 0, high-pressure fuel is connected to the leak orifice from the passage 55 around the flow guide 81 and flows well.

FIG. 7A shows the valve body 43 in the middle of its opening lift. The streamline distribution around the flow guide 81 is as shown in the figure, and the distribution of the pressure P acting on the head of the valve body 43 is as follows. As shown in FIG. 7B, due to the regulation of the fuel flow in the flow guide 81, the fuel pressure acting near the axis C of the valve body 43 becomes low, and the fuel pressure has a characteristic of having a peak outside of the axis C.

That is, when the valve body 43 is lifted to open, the high fuel pressure near the peak caused by the fuel flowing around the flow guide 81 acts on the valve body 43 just outside the opening of the orifice 80 in the valve opening direction. .

On the other hand, the fuel pressure that reaches the back pressure chamber 72 from the opening of the orifice 80 via the pressure balance passage 73 becomes a fuel pressure with reduced pressure near the axis C, and this low fuel pressure causes the valve body 43 to close. Acts on the direction.

This unbalance of acting force due to the difference in fuel pressure between the head of the valve body 43 and the back of the valve body 43 contributes to an increase in the opening force when the valve body 43 is lifted to open, so the valve body 43 quickly opens. Lift the valve to the open position.

When the valve opens, high-pressure fuel escapes into the fuel supply passage 8a via a leak orifice formed between the valve body 43 and the valve seat 59, but the area of this leak orifice determines the speed at which fuel pressure is released. Therefore, in this embodiment where the seat diameter is increased, the orifice area is expanded due to the increase in the seat diameter, so the injection pressure drops rapidly after the valve opens, as shown in Figure 5. The pressure becomes lower than the valve closing pressure of the nozzle 10.

For this reason, the injection rate also falls sharply at the end of injection, as shown in the figure, in line with this sudden drop in injection pressure, shortening the time until the end of injection.

Therefore, the valve opening drive of the valve body 43 is stable, so there is no need to increase the biasing force of the spring 51 in order to correct the unbalance of the acting force.
This keeps the electromagnetic force small.

As described above, according to the present invention, the fuel supply passage immediately upstream of the seat portion on which the valve body head is seated has a cross-sectional area that is slightly larger than the cross-sectional area of the opening of the pressure balance passage that penetrates the valve body head. A flow guide is provided at a position apart from the opening on the head side of the valve body of the pressure balance passage, and when the valve body is opened and lifted, the fuel pressure near the maximum due to the relief fuel flowing around the flow guide is applied to the valve body of the pressure balance passage. Since the flow of relief fuel is regulated so that it acts on the head of the valve body outside of the opening on the body head side, the imbalance between the forces acting on the head and back of the valve body assists the opening lift of the valve body. This results in the effect that the dynamic characteristics of the solenoid valve can be improved without increasing the driving electromagnetic force.

Furthermore, the stabilization of the dynamic characteristics of the electromagnetic valve provides the effect of improving the sharpness of the injection when the valve is opened.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a unit injector used in a conventional device, and FIG. 2 is a sectional view of a main part of FIG. 1. Fig. 3 is a schematic diagram of the unit injector according to the first embodiment of the present invention, Fig. 4 is an enlarged sectional view of the solenoid valve, and Fig. 5 is the valve body lift, injection pressure, and injection rate of the solenoid valve with respect to the applied voltage. It is a figure showing each characteristic of. FIG. 6A is an explanatory diagram of the action of the conventional device, FIG. 6B is a diagram showing the pressure distribution acting on the valve head, FIG. 7A is an explanatory diagram of the action of the present invention, and FIG. FIG. 4... Plunger, 7... Pressure chamber, 8a, 8b... Fuel supply passage, 10... Nozzle, 40... Solenoid valve, 43
...valve body, 48...sonorade, 51...spring,
55...Passage, 70...Cylinder, 71...Piston,
72...Back pressure chamber, 73...Pressure balance passage, 80...
Orifice, 81...Flow guide.

Claims (1)

[Claims] 1. A plunger that reciprocates in synchronization with the engine, a pressure chamber formed facing one end of the plunger, a nozzle that communicates with the pressure chamber and opens at a predetermined pressure or higher, and a fuel supply passage that communicates with the pressure chamber. Intervened,
Normally, the valve body is biased in the valve opening direction by an elastic member, and when the solenoid is energized, the valve body head lifts in the valve closing direction and seats on the seat, thereby closing the valve and facing the back of the valve body. A piston is provided integrally with the back of the valve body, and a back pressure chamber defined by the cylinder and the piston is penetrated from the piston facing the back pressure chamber to the head of the valve body. In the fuel injection control device, the fuel injection control device includes a valve device communicating with a fuel supply passage upstream of the seat portion through a pressure balance passage that opens and closes the valve device depending on the operating state of the engine. A flow guide having a cross-sectional area one size larger than the opening cross-sectional area of the pressure balance passage penetrating the valve body head is provided in the supply passage at a position spaced apart from the valve body head side opening of the pressure balance passage, When the valve body is opened and lifted, the relief fuel flow is controlled so that near maximum fuel pressure due to the relief fuel flowing around the flow guide acts on the valve body head outside of the valve body head side opening of the pressure balance passage. A fuel injection control device characterized by being regulated.