JPH0217178Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to the improvement of the discharge valve of a fuel injection pump used in a diesel engine, and is aimed at stabilizing the rotation speed in low speed and low load ranges and preventing cavities that occur in the injection system in high speed and high load ranges. suppression and improved durability,
Furthermore, it is intended to enable adjustment of the initial injection rate.

BACKGROUND OF THE INVENTION Fuel injection devices used in diesel engines, particularly vehicle diesel engines, have a large effect on output characteristics, exhaust gas characteristics, noise, etc., and have been improved in various ways. For example, the first
In the fuel injection device shown in the figure, a fuel injection pump 1 is connected to the fuel injection pump 1 from a fuel tank (not shown) via a feed pump.
The fuel fed into the plunger barrel 2 is guided to the feed boat 3 of the plunger barrel 2, and the fuel in the barrel chamber 5 in the plunger barrel 2 is pressurized by the action of the plunger 4, which moves up and down by a camshaft (not shown), and the pressurized fuel is discharged from the discharge valve. 6 to the discharge chamber 8 in the valve holder 7, and the pressurized fuel in the discharge chamber 8 is introduced into the injection pipe 9.
is sent to the injection nozzle 10 via. In the injection nozzle 10, the needle valve 1 is opened by the hydraulic pressure of the fuel that has reached the liquid reservoir chamber 11.
2 is lifted and fuel is injected into the cylinder 13.

Since the lift operation of the needle valve 12 of the injection nozzle 10 is performed based on the hydraulic pressure in the injection pipe 9, the steeper the drop after the peak of the hydraulic pressure, the better the injection is cut, and the leakage into the cylinder 13 is smooth. can be prevented. For this purpose, a discharge valve 6 is interposed between the barrel chamber 5 and the discharge chamber 8 to perform a suction back action to reduce the hydraulic pressure within the injection pipe 9.

The discharge valve 6 includes a valve seat 14, a valve body 15, and a spring 16, and communicates with the discharge chamber 8 when the valve is opened when the fuel in the barrel chamber 5 becomes high pressure, while the plunger 4 descends and the barrel chamber 5 becomes under low pressure. When the temperature starts to change, the valve body 15 begins to return due to the spring 16. The suction collar 15b below the seat surface 15a of the valve body 15 is connected to the center hole 1 of the valve seat 14.
The fuel from the discharge chamber 8 side is sucked back from the time when the valve body 15 starts to close with the upper edge of the valve body 4a until the seat surface 15a of the valve body 15 is seated on the valve seat 14 and the valve is completely closed, thereby reducing the hydraulic pressure of the fuel. Improves jet cutting.

However, after the discharge valve 6 is closed, the pressure inside the barrel chamber 5 becomes negative within the effective stroke range of the plunger 4, and bubbles are likely to occur. Once generated, the bubbles destabilize the amount of fuel in the barrel chamber 5, and when the plunger 4 enters its effective stroke again for pumping, it absorbs the compression energy and collapses, and the pressurized fuel is then pumped. Become. This results in fluctuations in injection timing and deterioration of injection quantity characteristics. For example, in a conventional fuel injection pump of the combination row type, the injection amount characteristic is constant at the lever in the low speed and low load region (the accelerator opening is constant when mounted on the vehicle);
In other words, when examining the relationship between the injection amount and the pump rotation speed, as shown in Figure 2, there is a large variation in the injection amount and pump rotation speed in the idling rotation region A. When the pump rotation speed increases, the injection amount decreases, but due to variations, when the pump rotation speed increases, the injection amount increases, and the rotation speed increases, or conversely, the rotation speed decreases. This phenomenon occurs, and the idling speed etc. become unstable, leading to deterioration of drivability.

On the other hand, in high-speed, high-load areas, etc., it is desirable to increase the injection rate and sharpen the injection break on the injection nozzle 10 side due to the fuel injection characteristics, which is said to be advantageous in terms of smoke generation and fuel efficiency. If this is done too quickly, air bubbles called cavities will occur within the injection pipe 9, which may cause cavitation corrosion. Furthermore, rapid injection failure, that is, rapid descent of the valve body 15 of the discharge valve 6, causes the valve body 15 to violently abut against the valve seat 14, reducing the life of the discharge valve 6.

In addition, from the perspective of noise countermeasures, which have become a big problem in recent years, the fuel injected into the cylinder 13 has an ignition delay, so a large amount of fuel is injected between the time it is injected and the time it ignites. Then, rapid combustion occurs after ignition, resulting in a large pressure fluctuation rate and causing noise. Therefore, there is a need for a fuel injection pump that can keep the injection rate low during the ignition delay period.

This idea was made in view of the current situation,
It is possible to stabilize the rotational speed in low-speed, low-load areas such as idling, and to maintain good fuel injection characteristics by rapidly performing suction in the early stages of suction, and in the latter stages, the effect is alleviated to prevent cavity formation. It is an object of the present invention to provide a discharge valve for a fuel injection pump, which can be restrained and seated comfortably, and can further adjust the initial injection rate. The configuration of the present invention that achieves this purpose includes a valve seat disposed between the barrel chamber of the plunger barrel, where fuel is pressurized by the plunger, and the discharge chamber of the valve holder, which communicates with the injection nozzle; In a discharge valve for a fuel injection pump, which is comprised of a valve body that is slidable while being pressed by a spring, the gap between the outer circumferential surface of the spring seat on the upper part of the valve body and the inner circumferential surface of the valve holder is reduced to allow the fuel to be retained. A seating buffer ring for buffering the seating of the valve body is provided close to the valve seat surface in the valve holder, and one end of the seating buffer ring communicates with the discharge chamber, and the other end is connected to a suction return collar for the valve body. The barrel chamber is characterized in that a communication passage is formed that opens within the lift range and communicates with the barrel chamber.

Hereinafter, one embodiment of the present invention will be described in detail based on the drawings.

The discharge valve of the fuel injection pump has a valve seat 21 and a valve body 2, as shown in FIG.
2, a spring 23, a seating buffer ring 24, and a valve holder 25, and the valve seat 21 has a central hole in the center that allows communication between the barrel chamber in the upper part of the plunger barrel and the discharge chamber 26 in the valve holder 25. 21a is formed, and a seating surface 21b is formed at the upper end thereof, and is disposed at the upper part of the plunger barrel. A valve body 22 is slidable in the center hole 21a of the valve seat 21, and the upper end surface of the valve body 22 is connected to the spring seat 21a.
2a, and an inverted conical seat surface 22 below it.
b is formed, and a suction/return collar 22c that slides on the center hole 21a is formed, and the lower end becomes a sliding guide portion 22d having a substantially cross-shaped cross section. The spring seat 22a of the valve body 22 and the valve holder 2
A spring 23 is interposed between the valve body 22 and the discharge chamber 26 of the valve body 22 to bias the valve body 22 in the valve closing direction.

On the other hand, the outer periphery of the upper end of the valve seat 21 has a small diameter, and a seating buffer ring 24 that allows the valve body 22 to be seated gently is fitted into this small diameter portion and fixed by a valve holder 25. The inner circumferential surface of this seating buffer ring 24 reduces the gap with the sealing surface 22b of the valve element 22 at a slightly upper position where the valve element 22 is seated, and reduces the gap between the upper end surface of the suction collar 22c and the sealing surface 22b. A buffering effect is achieved by a throttling action that limits the amount of fuel leaking. As shown in FIG. 4, this seating buffer ring 24 has an upper end communicating with the discharge chamber 26 which is the high pressure side above the valve body 22, and a lower end opening into the lift range of the suction return collar 22c of the valve body 22. A small diameter hole 27a serving as a communication path 27 is bored in the seating buffer ring 24.
A hole 27c is formed in the valve seat 21 and communicates with a circumferential groove 27b formed on the inner circumferential surface of the valve body 22. A communicating path 27 is constituted by these holes 27a, 27c and the circumferential groove 27b.

Discharge valve 20 of the fuel injection pump configured as above
In this case, the discharge chamber 26 on the high-pressure side of the upper part of the discharge valve 20 and the barrel chamber on the supply side are communicated through a communication passage 27, so when the plunger increases its effective stroke, the fuel in the barrel chamber on the upper part of the plunger barrel flows into the feed boat. The valve body 22 is gradually pressurized from the state where the fuel is being supplied, but the biasing force of the spring 23 and the residual pressure of the fuel remaining in the discharge chamber 26 act on the valve body 22 as a resultant force in the valve closing direction. Therefore, when the fuel is pressurized to a pressure that overcomes these resultant forces, the discharge valve 20 is opened and the fuel is guided from the barrel chamber to the discharge chamber 26 via the sliding guide portion 22d of the valve body 22. However, since the communication passage 27 is formed, when the valve body 22 rises and the suction return collar 22c rises, the hole 27c of the communication passage 27 opens, and the discharge valve 26 and the barrel chamber communicate with each other, and the pressure decreases once. Thereafter, the pressure is increased again, the discharge valve 20 is opened, and the liquid is injected from the discharge chamber 26 into the cylinder via the injection pipe and the injection nozzle. FIG. 5 shows the injection rate in this case, and the solid line indicates the discharge valve 20 of the present invention.
The one-dot chain line shows the case of a conventional discharge valve. As is clear from the figure, at the initial stage of injection, the injection rate changes as in the conventional case because the hole 27c of the communication passage 27 is closed by the suction collar 22c, and once the hole 27c of the communication passage 27 is opened, the injection rate changes. The injection rate decreases or is held substantially constant, and then changes with the peak shifted, that is, the initial injection rate becomes low.

Therefore, by changing the position of the hole 27c at the lower end of the communication passage 27 with respect to the suction return collar 22c and its diameter, it is possible to reduce the injection rate or change the crank angle or rate of change (inclination) at which the injection rate is kept substantially constant. In consideration of the ignition delay, the amount of fuel injected before ignition is reduced and the rate of pressure fluctuation during combustion is suppressed, thereby reducing noise.

Note that the position and diameter of this communication passage 27 vary depending on the specifications of the combustion chamber of the engine, etc., and are therefore appropriately selected.

After the fuel is injected into the cylinder,
When the plunger enters the downward stroke, the pressure in the discharge chamber 26 decreases, and the valve closing force acting on the valve body 22 increases, causing the valve body 22 to descend and return to the suction collar 22c.
Suction is performed from the point where the lower end reaches the upper end of the center hole 21a of the valve seat 21 in the same way as in the conventional case to improve injection cut-off.In the latter stage of suction, the seating buffer ring 24 seals the valve body 22. The amount of fuel escaping upward from the outer circumferential surface of the surface 22b is limited, and this throttling effect allows the valve body 22 to be seated comfortably. That is, the valve holder 25
In the upper part of the discharge chamber 26, when the valve body 22 is lowered, the amount of fuel that moves upward from between the outer circumferential surface of the spring seat 22a and the seat surface 22b and the inner circumferential surface of the valve holder 25 is The spring seat 22a of the valve body 22 at the mounting part of the seating buffer ring 24 is larger than that corresponding to the lowering.
Since the gap with the sealing surface 22b is small, the fuel that corresponds to the lowering of the valve element 22 cannot move upwards, but is subjected to throttling resistance, and the cushion effect causes the valve element 22 to be seated slowly.

Furthermore, at the same time as the cushioning effect of the seating of the valve body 22, a communication passage 27 that communicates the discharge chamber 26 and the barrel chamber is provided.
Therefore, during the downward stroke of the valve body 22, the barrel chamber is sealed by the suction collar 22c, and there is no negative pressure, and part of the fuel flows back through the communication passage 27 to the discharge chamber 26. Negative pressure is prevented by removing a portion of high-pressure fuel toward the lower-pressure barrel chamber. After this, the plunger is completely lowered and one stroke of the fuel injection pump is completed.

It is known that bubbles generated in the barrel chamber of a fuel injection pump generally change the discharge timing (crank angle deviation) as shown in the following equation, where the total volume of the bubbles is ΔV. The amount of variation Δθ in the discharge timing is determined by the number of pump rotations n and the setting force of the discharge valve.
If S ₁ is the cross-sectional area of the plunger, F is the average plunger speed, and Vpm is the average plunger speed, then the equation is as follows.

Δθ=6n(P ₀ +S ₁ −P ₁ /F・Vpm) ・(ΔV/(P ₀ +S ₁ )) As is clear from this equation, the barrel chamber and the discharge chamber 26 are communicated through the communication passage 27. Therefore, it is considered that since the supply pressure P ₁ can be brought close to the residual pressure P ₀ in the pipe, it is possible to keep ΔV relatively small.

When examining the relationship between the injection amount and the pump rotation speed at a constant lever of a fuel injection pump equipped with such a discharge valve 20, the relationship between the injection amount and the pump rotation speed in the idling rotation region A is as shown in FIG. It can be seen that the variation in values is reduced compared to the conventional one (Fig. 2).

Therefore, the idling speed is stabilized and drivability is improved.

In the above embodiment, the inner diameter of the seating buffer ring is smaller than the inner diameter of the valve holder and larger than the outer diameter of the spring seat and sealing surface of the valve body, but it is not necessarily limited to this. Since it is affected by the shape of the spring seat of the body, it is sufficient that at least a throttling effect can be given to the fuel escaping from the spring seat and the outer periphery of the sealing surface.

As explained above in detail with the embodiments, according to the present invention, the lowering speed of the valve body of the discharge valve is changed by the seated buffer ring, and the valve body is rapidly lowered in the early stage of sucking back, thereby improving fuel injection cut-off. At the same time, in the latter stage of sucking back, the sucking back speed can be slowed down so that the seat can be seated comfortably, suppressing the generation of cavities and preventing cavitation corrosion. Furthermore, since the valve body is seated loosely, the durability of the discharge valve is greatly improved. Furthermore, a communication passage is provided between the discharge chamber and the barrel chamber, and one end of the communication passage is opened in the lift range of the suction return collar of the valve body, so that the initial injection rate can be easily adjusted. Noise can be reduced by reducing the amount. Moreover, when the barrel chamber attempts to become negative pressure, fuel flows back from the discharge chamber, preventing this and suppressing the occurrence of cavities together with the action of the seating buffer ring. This stabilizes the amount of fuel in the barrel chamber during the next pressurization stroke of the plunger, prevents fluctuations in injection timing, and improves fuel efficiency and exhaust gas characteristics. Furthermore, the communication passage suppresses reflection of pressure waves within the injection pipe, thereby preventing secondary injection.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a fuel injection device equipped with a conventional discharge valve, Fig. 2 is an explanatory diagram of conventional injection quantity characteristics, and Fig. 3 is an embodiment of the discharge valve of the fuel injection pump of the present invention. 4 is a sectional view of the seating buffer ring, FIG. 5 is an explanatory diagram of the injection rate of the present invention, and FIG. 6 is an explanatory diagram of the injection quantity characteristics of the present invention. In the drawing, 20 is a discharge valve, 21 is a valve seat,
21a is a center hole, 22 is a valve body, 22a is a spring seat, 22b is a sealing surface, 22c is a suction collar, 23 is a spring, 24 is a seating buffer ring, 25 is a valve holder, 26 is a discharge chamber, and 27 is a communication passage. , 27a, 27c are holes, and 27b is a circumferential groove.

Claims (1)

[Scope of utility model registration request] A valve seat is arranged between the barrel chamber of the plunger barrel, where fuel is pressurized by the plunger, and the discharge chamber of the valve holder, which communicates with the injection nozzle, and the valve is slidable within this valve seat while being pressed by a spring. A discharge valve for a fuel injection pump consisting of a body includes a seating buffer ring that reduces the gap between the outer circumferential surface of a spring seat on the upper part of the valve body and the inner circumferential surface of the valve holder and cushions the seating of the valve body by the retained fuel. The seated buffer ring is provided close to the valve seat surface in the valve holder, and one end of the seated buffer ring communicates with the discharge chamber, and the other end opens within the lift range of the suction-return collar of the valve body and communicates with the barrel chamber. A discharge valve for a fuel injection pump, characterized in that a communication passage is formed to communicate with the fuel injection pump.