JP2000130293A - Fuel injector of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure higher injection pressure without increasing supply pressure from a pressure accumulating chamber. SOLUTION: This fuel injector is provided with a pressure accumulating chamber 1 for accumulating high-pressure fuel, a nozzle hole 5 provided on an oil storage chamber 4 into which fuel from the pressure accumulating chamber 1 is to be guided through an oil passage 7, and a valve 6 for opening and closing the nozzle hole 5. A dynamic pressure piston 23 to be moved according to differential pressure between the upstream side and the downstream side is provided on the way of the oil passage 7, the dynamic pressure piston 23 is moved in fuel injection, dynamic pressure is made to act on the oil storage chamber 4, and therefore, high injection pressure is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel injection device for a diesel engine.

[0002]

2. Description of the Related Art A common rail fuel injection device is known as a fuel injection device for a diesel engine. In this method, high-pressure fuel is temporarily stored in the common rail, and high-pressure fuel is injected directly into the combustion chamber by controlling the opening and closing of an electromagnetically-actuated fuel injection valve. There is an advantage that can be controlled.

As this fuel injection valve, Japanese Patent Application Laid-Open No. 9-158
Japanese Patent Application Laid-Open No. 811 proposes a configuration as shown in FIG.

The fuel in the accumulator 1 in the common rail into which the high-pressure fuel from the pump is fed is guided to the nozzle oil reservoir 4 via the high-pressure pipe 2 and the oil passage 7 inside the fuel injector 3 and the needles. It is guided via a filling orifice 11 to a hydraulic chamber 9 of a hydraulic piston 8 connected to a valve 6 via a lifter 12.

When fuel is not injected, the solenoid valve 14 is closed, whereby the high pressure of the hydraulic chamber 9 pushes the hydraulic piston 8, and the needle valve 6 is seated and closed against the return spring 13.

When injecting fuel, the solenoid valve 14 is opened and the pressure in the hydraulic chamber 9 is released to the low pressure side through the discharge orifice 10.
The needle valve 6 is lifted while pushing up, the injection hole 5 is opened, and fuel is injected.

When the same fuel pressure is applied, the pushing force of the hydraulic piston 8 is larger than the lifting force applied to the needle valve 6, and the needle valve 6 is closed. Even when the discharge orifice 10 is opened, the pressure in the hydraulic chamber 9 does not recover immediately because the filling orifice 11 is present, and the needle valve 6 is lifted while the solenoid valve 14 is open.

When the engine is stopped, the return spring 1 is used to prevent the fuel in the oil reservoir 4 from leaking.
3, the needle valve 6 is held closed.

[0009]

In such a fuel injection device, before the fuel injection, the pressure in the oil reservoir 4 is increased.
However, the pressure in the oil reservoir 4 decreases with the start of fuel injection, and the actual injection pressure during injection becomes lower than the set pressure in the pressure accumulator 1. This is because, before the fuel injection, the pressure from the pressure accumulating chamber 1 to the oil sump chamber 4 has a constant value in a static pressure state. Even if the pressure is reduced by the injection, the oil is injected from the oil sump chamber 4 through the injection hole 5. This is because there is a time delay before the fuel corresponding to the depleted fuel is supplied from the accumulator 1.

For this reason, in order to suppress the smoke under the operating condition of high engine speed and high load, it is necessary to further increase the supply pressure of the accumulator 1 by an amount corresponding to the pressure drop of the oil reservoir 4. Come.

However, when the pressure is increased as described above, new problems such as an increase in required pump driving force, a decrease in efficiency, a loss due to fuel leakage, a pressure resistance of piping, and an increase in required driving force of the solenoid valve are caused. It is becoming.

The present invention has been proposed to solve such a problem, and it is an object of the present invention to maintain a higher injection pressure without increasing a supply pressure from a pressure accumulation chamber.

[0013]

According to a first aspect of the present invention, there is provided a pressure accumulation chamber for storing high-pressure fuel, an injection hole provided in an oil reservoir through which fuel from the pressure accumulation chamber is guided through an oil passage, and an injection hole. In a fuel injection device for a diesel engine equipped with a valve that opens and closes, a dynamic pressure piston that moves in accordance with a pressure difference between the upstream and downstream of the oil passage is provided in the middle of the oil passage, and the dynamic pressure piston is moved during fuel injection to inject the injection pressure. Is maintained.

According to a second aspect, in the first aspect, the fuel pressure is introduced into the hydraulic chamber of the hydraulic piston from upstream of the dynamic pressure piston through a charging orifice, and the fuel pressure in the hydraulic chamber is released through a discharge orifice. An electromagnetic valve to be opened is provided, and the valve is lifted against the hydraulic piston by the fuel pressure of the oil reservoir when the electromagnetic valve is opened.

According to a third aspect of the present invention, in the first or second aspect, the dynamic pressure piston is slidably disposed in a cylinder chamber provided in the middle of an oil passage, and a fuel oil passage is provided in the dynamic pressure piston. It is formed through and is urged toward the upstream by a spring.

In a fourth aspect based on the third aspect, the dynamic pressure piston is formed as a stepped piston, a large-diameter portion is located on the upstream side of the fuel oil passage, a small-diameter portion is located on the downstream side, and the dynamic pressure piston is formed in the initial stage. The seat portion on which the large diameter portion is seated is provided at the position, and the pressure receiving area on the upstream side is small at the initial position and large after the start of the movement.

In a fifth aspect based on the fourth aspect, the small-diameter portion of the dynamic pressure piston is guided by a guide, and an annular spring chamber in which a return spring is interposed is formed around the small-diameter portion. It communicates with the discharge orifice.

[0018]

In the first to third aspects of the present invention, when the valve is opened to inject fuel, the pressure in the oil reservoir is greatly reduced with the injection of fuel, but the fuel pressure upstream of the dynamic pressure piston is reduced. Is small compared to this. Therefore, the dynamic pressure piston moves toward the oil reservoir due to the pressure difference between the upstream and the downstream, and pushes out the fuel, whereby the dynamic pressure acts on the oil reservoir to compensate for the decrease in the fuel pressure. As a result, the fuel injection pressure is immediately restored, and the high pressure is maintained. As a result, the fuel injection rate is increased, and the generation of smoke can be effectively reduced even at a high load with a large fuel injection amount.

According to the fourth aspect, the pressure receiving area on the upstream side of the dynamic pressure piston increases after the start of the movement of the dynamic pressure piston, so that the movement is accelerated and a larger dynamic pressure is applied to the oil reservoir. Thus, the fuel injection pressure can be maintained at a high level during the injection period.

According to the fifth aspect, the pressure of the spring chamber in which the return spring is interposed is rapidly decreased with the start of the fuel injection, so that the dynamic pressure piston can be moved quickly, and the responsiveness of the dynamic pressure generation is improved. Enhanced.

[0021]

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

In FIG. 1, 1 is a pressure accumulator, 2 is a high pressure pipe, 3 is an injector, 4 is a nozzle oil reservoir, 5 is an injection hole,
6 is a needle valve, 7 is an internal passage, 8 is a hydraulic piston, 9 is a hydraulic chamber, 10 is a discharge orifice, 11 is a filling orifice, 1
2 is a lifter, 13 is a return spring, and 14 is a solenoid valve, which are substantially the same as those shown in FIG.

According to the present invention, the pressure accumulating chamber 1 and the injector 3
A dynamic pressure piston 23 for generating a dynamic pressure at the start of fuel injection is provided in the middle of the high-pressure pipe 2 connecting the.

A connector 20 for connecting the high-pressure pipe 2 to the injector 3 is fixedly provided. A fuel oil passage 21 penetrates the center of the connector 20, and a fuel reservoir 22 having an enlarged diameter is formed at an outlet side thereof. I have. This fuel reservoir 22 is connected to the internal passage 7 and at this connection, a dynamic pressure piston 23
Are slidably housed in the cylinder chamber 26. The dynamic pressure piston 23 is urged toward the fuel pool 22 by a spring 25 and is in contact with the end of the connector 20.

The filling orifice 11 branches from the fuel reservoir 22 and connects to the hydraulic chamber 9.

In such a configuration, before fuel injection, there is no flow of fuel from the pressure accumulating chamber 1 to the nozzle oil reservoir 4, and the pressure is maintained at a constant pressure. In this state, the dynamic pressure piston 23 is pushed by the spring 25 and is at an upper position where it contacts the connector 20. The spring 2
Reference numeral 5 is only required to be able to return the dynamic pressure piston 23 in a static pressure state, and has a very weak spring force.

At the fuel injection timing, when the solenoid valve 14 is opened and high-pressure fuel is discharged from the discharge orifice 10,
The pressure in the hydraulic chamber 9 decreases, the needle valve 6 starts to rise, and the injection hole 5
, Fuel is injected. Thereby, the nozzle oil reservoir 4
, The pressure in the internal passage 7 decreases, and the pressure in the fuel reservoir 22 communicating with the hydraulic chamber 9 via the charging orifice 11 also decreases.

However, the amount of decrease in the fuel pressure is larger in the internal passage 7 than in the fuel reservoir 22 especially when the engine is heavily loaded with a large amount of fuel injection. Due to this pressure difference, the dynamic pressure piston 23 moves away from the connector 20 against the spring 25 and moves toward the internal passage, thereby pushing out the fuel toward the oil storage chamber 4, thereby causing the oil to be stored in the oil storage chamber 4. Apply high dynamic pressure to compensate for the decrease in fuel pressure.

In this case, the amount of movement of the dynamic pressure piston 23 may be determined so as to prevent a decrease in the pressure of the initial injection. For example, in the case of a 2-liter displacement diesel engine,
Injection amount of the high load region is approximately 70 mm ³ / st, considering that has caused a pressure drop to approximately 30 mm ³ / st in the initial injection amount, the internal passage only 30 mm ³ by the movement of the dynamic pressure piston 23 7 May be reduced. Now, let the diameter of the dynamic pressure piston 23 be 5 mm,
If the diameter is 2 mm, the movement amount may be about 3 mm. However, due to the initial pressure difference, the dynamic pressure piston 23
Starts moving, and further moves in the same direction due to its inertia force to obtain the effect of giving the pressure increase on the oil reservoir chamber 4 side as a dynamic pressure. It is set to 6 mm, which is longer than that.

FIG. 3 shows how the fuel injection pressure changes. In the prior art, the pressure P1 in the oil storage chamber 4 decreases greatly with the start of fuel injection, whereas the fuel pressure P1 on the upstream inlet side decreases.
2 is lowered slightly by the release of discharge orifice 10. By the time high pressure fuel is supplied from the upstream side to increase the pressure to the original pressure, about half of the fuel injection has been completed due to the pipe resistance of the internal passage 7 and the like.

On the other hand, in the present embodiment, the upstream pressure P2 decreases due to the movement of the dynamic pressure piston 23 due to the differential pressure between the upstream pressure P2 at the initial stage of the injection and the downstream pressure P1. Starts to rise from the middle. The dynamic pressure piston 23 is displaced in accordance with this pressure difference, whereby the pressure drop of the pressure P1 in the oil reservoir 4 is greatly reduced.

For this reason, as shown in FIG. 4, the fuel injection rate is increased, and as shown in FIG. 5, the generation of smoke is significantly reduced as compared with the conventional art, especially at a high load where the fuel injection amount is large. It becomes possible to reduce to.

When the solenoid valve 14 is closed and the needle valve 6 is seated and fuel injection is stopped, the oil reservoir 4 and the internal passage 7 are immediately filled with high-pressure fuel, and the fuel upstream of the dynamic pressure piston 23 is discharged. It rises to the same pressure as the pressure of the reservoir 22. As a result, the dynamic pressure piston 23 is pushed back by the spring force of the spring 25 until the next injection, and returns to the initial position where it comes into contact with the connector 20 to prepare for the next injection.

Next, another embodiment shown in FIG. 6 will be described.

This has a stepped dynamic pressure piston 31, and a cylindrical guide 33 is provided inside the cylinder chamber 26, and the small diameter portion 3 of the dynamic pressure piston 31 is provided by the guide 33.
1a is slidably guided. The annular spring chamber 36 between the small diameter portion 31a and the cylinder chamber 26 is
It communicates with the discharge orifice 10 through 7 and a return spring 35 is interposed here.

A very small diameter oil passage 32 penetrates the center of the dynamic pressure piston 31. The large diameter portion 31b of the dynamic pressure piston 31
It is pushed by the return spring 35 and retreats until it comes into close contact with the tubular seat portion 29 fitted to the connector 20. The pressure receiving area of the dynamic pressure piston 31 facing the fuel reservoir 22 when seated on the seat portion 29 is set to be substantially the same as the pressure receiving area of the fuel reservoir chamber 39 facing the small diameter portion 31a. The fuel storage chamber 39 includes the internal passage 7 and the tapered passage 3.
The fuel reservoir chamber 39 is formed so as to have a volume equal to or greater than the maximum fuel injection amount.

The filling orifice 11 communicates with the fuel reservoir 22 via a passage 41 passing through the seat 29.

With this construction, when the discharge orifice 10 is opened by the opening of the solenoid valve 14 and fuel injection is started, the pressure in the fuel reservoir 22 slightly decreases while the oil reservoir 22 decreases. 4. The pressure in the internal passage 7 is greatly reduced as fuel is injected. At the same time, the pressure in the spring chamber 36 is significantly reduced because the oil passage 37 is open to the filling orifice 10.

As a result, the dynamic pressure piston 31 starts to move toward the fuel storage chamber 39 while resisting the return spring 35 based on the pressure difference. When the dynamic pressure piston 31 separates from the seat portion 29, the large-diameter portion 31b
, The pressure of the fuel pool 22 is applied, and the moving speed of the dynamic pressure piston 31 is accelerated. As a result, the pressure in the fuel storage chamber 39 increases. At this time, the oil passage 32 provided in the dynamic pressure piston 31 has a very small diameter, thereby preventing the pressure in the fuel storage chamber 39 from escaping to the upstream side. Fuel pool 39
Even if the pressure increases, the dynamic pressure piston 31 moves by inertia, so that the fuel pressure further increases, and the fuel further increases in pressure by the tapered flow path 34.

In this manner, a high dynamic pressure acts on the oil reservoir 4, and the pressure injected from the injection hole 5 is maintained at a high level. FIG. 7 shows a change in the fuel injection pressure. The fuel pressure P1 in the oil reservoir 4 depends on the operation of the dynamic pressure piston 31 and the taper flow path 3.
Due to the pressure wave generated by 4, the pressure becomes higher than that of the pressure accumulation chamber 1, and high-pressure injection can be performed.

Therefore, as shown in FIG. 8, the fuel injection rate is higher than that of the first embodiment, and as a result, as shown in FIG. Torque can also be increased.

It should be noted that the present invention is not limited to the above-described embodiment, and it is apparent that various modifications can be made within the scope of the technical idea of the present invention. For example, the fuel injection valve is not limited to the one that lifts the needle valve by fuel pressure balance, and may be one that directly drives the needle valve by an electromagnetic valve.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is an explanatory diagram showing a fuel injection pressure in comparison with a conventional case.

FIG. 4 is an explanatory diagram showing a fuel injection rate in comparison with a conventional case.

FIG. 5 is an explanatory diagram showing a relationship between a fuel injection amount and a generation amount of smoke in comparison with a conventional case.

FIG. 6 is a cross-sectional view showing a second embodiment.

FIG. 7 is an explanatory diagram showing a fuel injection pressure in comparison with a conventional case.

FIG. 8 is an explanatory diagram showing a fuel injection rate in comparison with a conventional case.

FIG. 9 is an explanatory diagram showing a relationship between a fuel injection amount, smoke, and torque in comparison with the related art.

FIG. 10 is a sectional view showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Accumulation chamber 3 Injector 4 Oil reservoir 5 Injection hole 6 Needle valve 8 Hydraulic piston 9 Hydraulic chamber 10 Release orifice 11 Filling orifice 14 Solenoid valve 22 Fuel reservoir 23 Dynamic pressure piston 24 Fuel oil passage 25 Spring 29 Seat part 31 Dynamic pressure piston 31a small diameter portion 31b large diameter portion 32 fuel oil passage 35 return spring 36 spring chamber

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) F02M 61/20 F02M 61/20 PF Term (Reference) 3G066 AA07 AB02 AC09 AD12 BA05 BA12 BA13 BA16 BA19 BA24 CB05 CC06T CC08T CC14 CC26 CC61 CC64T CC66 CC67 CC68U CC70 CD28 CD30 CE13 CE22 CE34 DA06 DA08 DA11 DA12 DA14 DB09

Claims (5)

[Claims] 1. An accumulator for storing high-pressure fuel, an injection hole provided in an oil reservoir through which fuel from the accumulator is guided through an oil passage,
In a fuel injection device for a diesel engine having a valve for opening and closing an injection hole, a dynamic pressure piston that moves in accordance with a pressure difference between upstream and downstream of the oil passage is provided in the middle of the oil passage, and the dynamic pressure piston moves during fuel injection. A fuel injection device for a diesel engine, characterized in that the injection pressure is maintained. 2. An electromagnetic valve is provided in a hydraulic chamber of a hydraulic piston to guide fuel pressure from upstream of the dynamic pressure piston through a charging orifice and to release fuel pressure in the hydraulic chamber through a discharge orifice. 2. The diesel engine fuel injection device according to claim 1, wherein the valve is lifted against the hydraulic piston by the fuel pressure of the oil reservoir when the valve is opened. 3. The dynamic pressure piston is slidably disposed in a cylinder chamber provided in the middle of an oil passage. A fuel oil passage is formed through the dynamic pressure piston, and the dynamic pressure piston is directed upstream by a spring. The fuel injection device for a diesel engine according to claim 1, wherein the fuel injection device is energized. 4. The seat according to claim 1, wherein said dynamic pressure piston is formed as a stepped piston, a large diameter portion is located upstream of the fuel oil passage, a small diameter portion is located downstream, and a large diameter portion is seated at an initial position. Is provided, the pressure receiving area on the upstream side is small at the initial position,
The fuel injection device for a diesel engine according to claim 3, wherein the fuel injection device is configured to increase after the start of the movement. 5. A small-diameter portion of the dynamic pressure piston is guided by a guide, and an annular spring chamber having a return spring interposed therebetween is formed around the small-diameter portion, and the spring chamber communicates with the discharge orifice. 5. The fuel injection device for a diesel engine according to 4.