JPH06117344A - Fuel injection pump - Google Patents

Abstract

PURPOSE:To provide a fuel injection pump capable of mitigating seating shock of a delivery valve without having bad influence on exhaust gas, a combustion state and others and extensively reducing collision sound of the delivery valve and a valve seat. CONSTITUTION:Under a piston part 2b to block a fuel passage 7 of a delivery valve 2 to open and close by being guided by the fuel passage 7 of a delivery valve guide 4, a first restriction part 2d formed by bulging this delivery valve 2 in the circumferential direction and a second restriction part 2e formed by bulging the delivery valve 2 in the circumferential direction under this first restriction part 2d are provided, and simultaneously, a communicating passage 13 to communicate a wall surface under this second restriction part 2e and a wall surface between the first restriction part 2d and the piston part 2b through to each other is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection pump for a diesel engine, and more particularly to a fuel injection pump capable of reducing impact noise when a delivery valve is seated on a valve seat.

[0002]

2. Description of the Related Art As shown in FIG. 6, a delivery valve 2 of a fuel injection pump 1 is closed when the delivery of fuel by a plunger 3 is completed, and the fuel flows backward from a fuel injection pipe (not shown) to the fuel injection pump. In addition to preventing this, the delivery valve 2 itself sucks back and improves the disconnection of the injection from the fuel injection nozzle (not shown), and drools (a phenomenon in which fuel is granularly accumulated at the tip of the fuel injection nozzle after the end of injection). Is to prevent.

Generally, the delivery valve 2 is assembled at a position as shown in the drawing, and the delivery valve 2 has a conical portion 2a having a sealing surface which is in close contact with the valve seat 4a and a piston below the conical portion 2a. A guide portion 2c having a cross shape in a plan view, which fits with the portion 2b and the delivery valve guide 4 and serves as a guide, is formed. Now, as the plunger 3 rises, the fuel pressure in the plunger barrel 5 rises, and when it reaches a specified value, the delivery valve 2 is pushed up and the fuel is pumped to the fuel injection pipe. Then, after the oil supply work by the plunger 3 is completed, the pressure in the plunger barrel 5 is rapidly lowered, so that the delivery valve 2 is caused by the valve spring 6 to move to the valve seat 4a.
It closes rapidly as if struck against, preventing backflow of fuel from the fuel injection pipe.

At this time, the piston portion 2b first blocks the fuel passage 7, and the conical portion 2a is further closed by the valve seat 4a.
Since the delivery valve 2 sinks until it comes into close contact with the fuel injection pipe, the fuel pressure in the fuel injection pipe is reduced by the amount of the sinking. In this way, it is possible to prevent the fuel from running out of the fuel injection nozzle and prevent dripping.

[0005]

By the way, as described above, the delivery valve 2 closes abruptly after the fuel injection is completed. Therefore, the seating impact of the delivery valve 2 causes a large noise over the entire fuel injection pump 1 to cause a diesel engine. As the overall noise reduction progresses, the noise associated with the seating of the delivery valve 2 has become non-negligible.

Therefore, in order to deal with such a problem, a damping valve (ball valve) 8 as shown in FIG. 7 is used.
A fuel injection pump 1 using a delivery valve holder 9 with a mark has been put into practical use. This is because the damping valve 8 is opened when the fuel is pressure-fed from the plunger 3, and the fuel is pressure-fed to the fuel injection nozzle mainly through the central passage 11 of the stopper 10. After the injection is completed, the damping valve 8 is faster than the delivery valve 2. In order to be seated, in the sucking back process, the internal pressure of the pipe is reduced by the sucking back amount through the orifice 12 beside the stopper 10. For this reason, the valve closing operation of the delivery valve 2 becomes relatively slow, a sudden pressure drop is avoided, the seating impact is alleviated, and cavitation does not occur.

However, according to this device, the pressure drop at the end of fuel injection becomes relatively slow, so that the injection end timing is delayed and the exhaust gas deteriorates (especially, HC, CO, etc. increase). There was a problem. On the other hand, Japanese Patent Application Laid-Open No. 51-65233 and Japanese Utility Model Laid-Open No. 52-143526.
In Japanese Patent Publication No. JP-A-2003-264, too, a throttling portion for narrowing the cross-sectional area of the fuel passage is provided to reduce the descending speed of the delivery valve, softening the seating impact between the delivery valve and the valve seat during seating, and generating noise. A device that suppresses the above has been proposed.

According to these devices, as shown in the fuel flow rate characteristic of FIG. 5, the time t ₄ when the delivery valve is closed in the conventional fuel injection pump not having the throttle portion of FIG. Although the flow rate change during t ₅ is extended between time t ₄ and t ₆ as shown in FIG. 5 (b) by the flow path resistance of the throttle portion to alleviate the seating impact, the above-mentioned change occurs even when the valve is opened. Since the throttle portion serves as the flow path resistance, the change in the fuel flow rate at the time of opening the valve extends between time t _{1 and} time t _3, and it becomes impossible to smoothly pump the fuel to the injection nozzle at the initial stage of fuel injection. There is a problem that the ignitability deteriorates and it becomes difficult to maintain a good combustion state.

As described above, in the prior arts listed above, it is difficult to reduce the seating impact without adversely affecting the exhaust gas, the combustion state, etc. Due to the design, there is a problem that it cannot be adopted if there is little room. In view of the above problems, the present invention can alleviate the seating impact of the delivery valve without adversely affecting the exhaust gas, the combustion state, etc., and thus can significantly reduce the collision noise between the delivery valve and the valve seat. An object of the present invention is to provide a fuel injection pump that can be used.

[0010]

A fuel injection pump according to the present invention for achieving the above object is provided below a piston portion which blocks the fuel passage of a delivery valve which is opened and closed by being guided by the fuel passage of a delivery valve guide. A first throttle portion formed by bulging the delivery valve in the circumferential direction, and a second throttle portion formed by bulging the delivery valve in the circumferential direction below the first throttle portion, A communication passage that connects a wall surface below the second throttle portion and a wall surface between the first throttle portion and the piston portion is provided.

The first throttle portion and the second throttle portion narrow the cross-sectional area of the fuel passage of the delivery valve guide with a certain gap between the first throttle portion and the second throttle portion and the inner wall surface of the delivery valve guide. It also has a role as a guide member for stabilizing the posture of the delivery valve, and is configured to form a kind of chamber substantially between the first throttle portion and the second throttle portion. There is.

Further, the communication passage includes a first throttle portion and a second throttle portion.
This is a bypass passage for the fuel passing through the throttle portion, and in the descending stroke of the delivery valve, this communication passage leading to the first throttle portion becomes the flow passage for the fuel to be returned to the plunger barrel together with the second throttle portion. In the ascending stroke of the valve, the communication passage is mainly configured to serve as a flow path for fuel that is pressure-fed toward the fuel injection nozzle.

[0013]

[Operation] The fuel injection pump of the present invention has the above-mentioned configuration, and in the descending stroke of the delivery valve, the fuel existing below the piston portion passes through the first throttle portion and the second throttle portion, Since it is gradually returned to the plunger barrel, the seating speed of the delivery valve is reduced, and it acts to reduce the generation of noise due to seating impact.

On the other hand, in the ascending stroke of the delivery valve, the fuel is pressure-fed through the communication passage so as to push up the piston portion vigorously, so that the first throttle portion and the second throttle portion have a flow path resistance. It is possible to prevent such deterioration, prevent deterioration of ignitability in the early stage of combustion, and stabilize the combustion state.

[0015]

EXAMPLES Next, an example of the present invention will be described with reference to the drawings. In the fuel injection pump 1 of the present embodiment shown in FIGS. 1 and 2, the delivery valve 2 has a conical portion 2a which is in close contact with the valve seat 4a of the delivery valve guide 4.
A piston portion 2b that blocks the fuel passage 7 is formed below the conical portion 2a. Further, the delivery valve 2 has a first throttle portion 2d and a second throttle portion 2d formed by circumferentially expanding the delivery valve 2 in order to narrow the flow passage area of the fuel returned to the inside of the plunger barrel 5. The portion 2e is formed.

Further, the second throttle portion 2e is formed to have a smaller diameter than the first throttle portion 2d, and when the delivery valve 2 is seated, the delivery valve guide 4 is arranged so as to come close to the second throttle portion 2e. An annular protrusion 4b is formed on the inside of the. Then, the first throttle portion 2d and the second throttle portion 2e gradually reduce the fuel existing between the first throttle portion 2d and the second throttle portion 2e, respectively, between the first throttle portion 2d and the inner wall surface of the delivery valve guide 4. It has gaps 7a and 7b for returning to the plunger barrel 5.

Further, the wall surface of the delivery valve 2 below the second throttle portion 2e, the piston portion 2b and the first
A communication passage 13 that communicates with the wall surface of the delivery valve 2 between the narrowed portion 2d is formed. When the fuel injection pump 1 of the present embodiment is in the downward stroke of the delivery valve 2 shown in FIG. 2, first, in the state of FIG. 2 (a) in which the piston portion 2b blocks the fuel passage 7, the second throttle portion 2e. A large flow passage cross-sectional area is still left between the second projection 2b and the annular projection 4b, and the fuel existing below the first restriction 2d passes between the second restriction 2e and the annular projection 4b. Then, the delivery valve 2 is returned to the inside of the plunger barrel 5, and the descending speed of the delivery valve 2 at this time is equivalent to that of the conventional one which does not have a mechanism for absorbing seating impact.

Further, as the delivery valve 2 descends as shown in FIG. 2B, the second throttle portion 2e faces the annular projection 4b and narrows the fuel flow passage cross-sectional area. As shown in FIG.
A type of chamber 7c is formed between the first and second chambers 7c and 7e, and the fuel in the chamber 7c passes through the communication passage 13 from the gap 7a between the first throttle portion 2d and the inner wall surface of the delivery valve guide 4. From the route and the route passing through the gap 7b between the second throttle portion 2e and the annular projection 4b of the delivery valve guide 4, it is gradually returned into the plunger barrel 5, and the descending speed of the delivery valve 2 is greatly reduced. .

As described above, the delivery valve 2 whose descending speed is greatly reduced is, as shown in FIG. 2C, a valve of the delivery valve guide 4 in a state where the volume of the chamber 7c is reduced. Since the seat 4a is gently seated, the seating impact between the valve seat 4a and the conical portion 2a of the delivery valve 2 is small, and the noise due to the seating impact is significantly reduced.

On the other hand, in the ascending stroke of the delivery valve 2, as shown in FIG. 4, fuel is pumped mainly through the communication passage 13 so as to push up the piston portion 2b, and the first throttle portion 2d and the second throttle portion 2d. It is possible to prevent the portion 2e from becoming a flow path resistance, and since a small amount of fuel flows into the chamber 7c from the gap 7b between the second throttle portion 2e and the annular protrusion 4b of the delivery valve guide 4, this chamber 7c It is possible to smoothly perform fuel injection in the initial stage of combustion without generating negative pressure inside.

As a result, even though the delivery valve 2 has the throttle mechanism for alleviating the seating impact of the delivery valve 2, when the delivery valve 2 is opened, the throttle mechanism does not become a resistance to fuel pressure feeding. As shown in (c), when the valve is open, the flow rate can be increased in a short time between time t _{1 and} t ₂ , and when the valve is closed, the flow rate is relatively slowly during time t _{4 to} t _6. Is reduced.

Therefore, the fuel can be smoothly pumped in the initial stage of injection, the ignitability is not impaired, the seating impact of the delivery valve 2 can be alleviated, and the noise of the fuel injection pump 1 can be reduced. Can be done.

[0023]

According to the fuel injection pump of the present invention, the delivery valve is expanded in the circumferential direction below the piston portion of the delivery valve that opens and closes by being guided by the fuel passage of the delivery valve guide. A first throttle portion formed as described above, and a second throttle portion formed by bulging the delivery valve in the circumferential direction below the first throttle portion, and a wall surface below the second throttle portion, The first
Since the communication passage that connects the wall surface between the throttle portion and the piston portion is provided, the following effects can be obtained.

In the descending stroke of the delivery valve, the fuel existing below the piston portion is gradually returned to the plunger barrel through the first throttle portion and the second throttle portion.
The seating speed of the delivery valve is reduced, and the generation of noise due to seating impact can be reduced. On the other hand, in the ascending stroke of the delivery valve, the fuel is pressure-fed through the communication passage so as to push up the piston portion vigorously, so that the first throttle portion and the second throttle portion become flow path resistance. This can be avoided, deterioration of ignitability at the initial stage of combustion can be prevented, and the combustion state can be stabilized. Therefore, the seating impact of the delivery valve can be alleviated without adversely affecting the exhaust gas, the combustion state, and the like, and thus a quiet fuel injection pump can be provided.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a fuel injection pump according to an embodiment of the present invention.

FIG. 2 shows a descending stroke of a delivery valve used in the fuel injection pump of FIG. 1, (a) is a cross-sectional view of a state in which a piston portion blocks a fuel passage, and (b) is a second throttle portion. Is a sectional view of a state in which the conical portion faces the annular protrusion, and FIG.

FIG. 3 is a sectional view of the descending stroke of the delivery valve located at the position of FIG. 2 (b).

FIG. 4 is a cross-sectional view of the delivery stroke of the delivery valve located at the position of FIG. 2 (b).

5 is a timing chart showing changes in the fuel flow rate when the delivery valve used in the fuel injection pump of FIG. 1 is opened and closed, and FIG. 5A is a conventional chart that does not have a throttle mechanism for cushioning seating impact. Is the characteristic of the fuel injection pump of FIG. 1, (b) is the characteristic of the conventional fuel injection pump having a throttle mechanism for cushioning the seating impact, and (c) is the characteristic of the fuel injection pump of the present invention.

FIG. 6 is a partial cross-sectional view of a conventional fuel injection pump.

FIG. 7 is a cross-sectional view of a delivery valve holder used in a conventional fuel injection pump.

[Explanation of symbols]

1 Fuel Injection Pump 2 Delivery Valve 2b Piston Part 2d First Throttling Part 2e Second Throttling Part 4 Delivery Valve Guide 7 Fuel Passage 13 Communication Passage

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiromitsu Tozaki 8 Tsutana, Fujisawa City, Kanagawa Prefecture

Claims (1)

[Claims] 1. A first throttle portion formed by bulging the delivery valve in the circumferential direction, below a piston portion of the delivery valve that opens and closes by being guided by the fuel passage of the delivery valve guide. A second throttle portion formed by bulging the delivery valve in the circumferential direction is provided below the first throttle portion, and a wall surface below the second throttle portion, the first throttle portion and the piston portion. A fuel injection pump having a communication passage communicating with a wall surface between the fuel injection pump and the wall surface.