JPH04241769A - Delivery valve for fuel injection pump of internal combustion engine - Google Patents

Abstract

PURPOSE:To stabilize injection by suppressing decrease of a residual pressure in a fuel pipe from a low speed rotational region to a high speed rotational region while preventing secondary injection and irregular injection from an injection nozzle. CONSTITUTION:A valve unit 22, movably housed reciprocated in a valve case 21, has a large diameter part 22a fittable to a valve seat 21b of the valve case 21. The valve unit 22 is energized in a direction of pressing the large diameter part 22a to the valve seat 21b by a compression coil spring 15. A passage, passing through a plunger chamber side end part and an injection nozzle side end part of the valve unit 22, is provided with the first orifice 31, second orifice 32 of diameter smaller than or equal to bore size of the first orifice, expansion chamber 25 and balls 26. Thus by damping a reflecting wave of fuel from an injection nozzle in two stages by the first and second orifices 31, 32 without excessively opening the balls 26 just after fuel injection action, a residual pressure in a fuel pipe is held to a fixed value.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge valve for a fuel injection pump of an internal combustion engine.

0002

2. Description of the Related Art Conventionally, various improvements have been made to the discharge valves provided in fuel injection pumps in order to prevent secondary injection and irregular injection in diesel engines. for example,
The device disclosed in Japanese Patent Application Laid-Open No. 47-29715 provides a hollow chamber in the middle of a through hole formed inside the discharge valve body, and this hollow chamber absorbs the energy of the fuel pressure wave, thereby reducing the Suppresses the occurrence of subsequent injection. Furthermore, JP-A-56-
As disclosed in Japanese Patent Publication No. 115849 and Japanese Patent Publication No. 63-39792, in which a first valve body that opens when fuel is pumped and a second valve body that opens in the opposite direction are combined, the first valve body opens in the opposite direction. Immediately after the fuel injection operation when the second valve element closes, if the pressure (residual pressure) in the fuel pipe leading to the fuel injection nozzle is high, the second valve element opens, which reduces the pressure and maintains it at a predetermined value. secondary injection is prevented.

0003

[Problems to be Solved by the Invention] However, Japanese Patent Application Laid-Open No. 56-115849 and Japanese Patent Publication No. 63-3979
In the discharge valve disclosed in Publication No. 2, when the fuel in the fuel pipe is released to the plunger chamber by opening the second valve body immediately after the fuel injection operation, the reflected wave from the injection nozzle passes through the orifice in the high speed rotation range. Since the fuel may excessively open the second valve body, the residual pressure in the fuel pipe tends to become lower than the valve opening set pressure of the second valve body. Therefore, in the high speed range,
The residual pressure in the fuel pipe may drop and cause irregular injection. On the other hand, if the second valve body is prevented from opening excessively by reducing the hole diameter of the orifice and reducing the fuel flow rate passing through the orifice, it is possible to prevent the residual pressure in the fuel pipe from decreasing in the high speed rotation range. However, there is a problem in that it is difficult to attenuate the reflected wave from the fuel injection nozzle by the orifice, making secondary injection more likely to occur.

The present invention has been made to solve these problems, and it prevents irregular injection and secondary injection from the injection nozzle, and also eliminates the residue in the fuel pipe from the low-speed rotation range to the high-speed rotation range. It is an object of the present invention to provide a discharge valve for a fuel injection pump that suppresses a drop in pressure and stabilizes injection.

[0005]

[Means for Solving the Problem] To achieve this, the discharge valve for a fuel injection pump for an internal combustion engine of the present invention is a fuel injection pump for an internal combustion engine that pressurizes fuel in a plunger chamber by the compression movement of a plunger and injects it from an injection nozzle. The valve case is a cylindrical valve case through which fuel can flow, and has an annular valve seat on the inner circumferential wall of one end of the case; a valve body having a large-diameter portion that can be brought into contact with the valve body; urging means for biasing the valve body in a direction to press the large-diameter portion against the annular valve seat; and a plunger chamber side end portion of the valve body; a first orifice formed in a passage passing through the injection nozzle side end; and a second orifice formed in the passage on the plunger chamber side of the first orifice and having a diameter smaller than or equal to the hole diameter of the first orifice. an expansion chamber formed in the passageway between the first orifice and the second orifice; and an expansion chamber provided in the passageway on the plunger chamber side of the second orifice, the expansion chamber being provided in the passageway on the plunger chamber side of the second orifice, and extending in the direction from the injection nozzle to the plunger chamber side. A check valve that allows the fuel in the passage to flow only through the passage.

[0006]

[Operation] According to the fuel injection pump of the present invention, when the fuel in the fuel pipe is released to the plunger chamber side immediately after the fuel injection operation, the valve body is closed and the first orifice and this first
A second orifice having a diameter smaller than or equal to the diameter of the orifice restricts the fuel flow rate. Therefore, by mutually adjusting the first orifice and the second orifice, the residual pressure in the fuel pipe can be maintained at a constant pressure without opening the check valve excessively from the low speed rotation range to the high speed rotation range, thereby preventing irregular injection. prevent. Further, since the reflected wave of the fuel generated in the fuel pipe is attenuated in two stages by the first orifice and the second orifice, it is possible to suppress the occurrence of secondary injection.

[0007]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. FIG. 2 shows a fuel injection pump applied to a diesel engine. The fuel injection pump 1 transmits the driving force of the diesel engine to the drive shaft 2, and causes the plunger 4 to reciprocate within the cylinder 8 via the coupling 3. A housing 13 that accommodates the cylinder 8 is formed with a fuel supply hole 12 that can communicate with the plunger chamber 10, and a discharge valve 5 that is communicated with the fuel supply hole 12 is fixed. A fuel pipe 6 is connected to the discharge valve 5, and an injection nozzle 7 is connected to the tip of the fuel pipe 6. When the fuel introduced into the plunger chamber 10 from the fuel introduction hole 9 formed in the cylinder 8 is compressed by the compression stroke of the plunger 4 and the fuel supply hole 11 and the fuel supply hole 12 communicate with each other, the fuel in the plunger chamber 10 is It is fed under pressure to the discharge valve 5. When the fuel pressure exceeds the valve opening setting pressure of the discharge valve 5, the flow from the discharge valve 5 to the fuel pipe 6 and the injection nozzle 7
After that, fuel is injected into each cylinder of the diesel engine.

To explain the discharge valve 5 in detail, as shown in FIG. 1, a valve body 22 is inserted into a guide hole 21a of a valve case 21 fixed to a housing 13 from the nozzle side. A spring seat 29 is press-fitted into the plunger chamber side end 21c of the guide hole 21a, and the holder 27 and the ball 26 are pressed against the valve body 22 by the compression coil spring 28 that comes into contact with the spring seat 29. Compression coil spring 28
The set pressure is set lower than the set pressure of the compression coil spring 15 that presses the valve body 22 against the valve seat 21b, which is an annular valve seat formed in the valve case 21, toward the plunger chamber.

The valve body 22 has a sliding portion 22c that is slidable in the guide hole 21a, and an annular groove 33 is formed on the injection nozzle side of the sliding portion 22c. A gap is formed between the inner wall surface of the guide hole 21a and the sliding portion 22c, through which fuel can pass from the plunger chamber side to the injection nozzle side. On the injection nozzle side of the annular groove 33 of the valve body 22, a conical slope 22b that can be seated on the valve seat 21b is formed in the large diameter portion 22a. Valve body 2
2 is formed with a passage passing through from the injection nozzle side to the plunger chamber side, and a first orifice 31 is formed in this passage.
, expansion chamber 25, second orifice 32 and annular slope 25
a is formed. The first orifice 31 has a concave portion 21d
An opening is formed in the ring 30 which is press-fitted into the ring 30. The diameter of the expansion chamber 25 is larger than the diameter of the first orifice 31 . The diameter of the second orifice 32 is set smaller than that of the first orifice 31. Annular slope 25 communicating with second orifice 32
A ball 26 can be seated on a. Spring seat 29
A fuel passage 29a is formed therein.

When fuel is force-fed from the plunger to the injection nozzle, when the valve body 22 is lifted toward the injection nozzle against the compression coil spring 15 by the pressure of the fuel flowing inside the valve case 21, the valve body 22 is lifted toward the injection nozzle. Fuel flows through the gap between the sliding part 22c and the guide hole 21a, and the valve seat part 21b
Fuel flows toward the injection nozzle from between the conical slope 22b and the conical slope 22b. At this time, the ball 26 is compressed by the compression coil spring 28.
Due to the urging force of , it follows the valve body 22 and moves to the right in FIG. Therefore, since the ball 26 serving as a check valve comes into contact with the annular slope 25a, fuel does not flow into the second orifice. When the valve body 22 is seated on the valve seat 21b after the end of the pressure feeding of fuel,
A reflected wave of the fuel acts on the valve body 22 from the injection nozzle side, and the fuel passing through the first orifice 31 enters the expansion chamber 25.
It enters the second orifice 32. When the pressure of this fuel exceeds a certain pressure, the ball 26 moves to the compression coil spring 28.
When the ball 26 lifts from the annular slope 25a against the pressure and decreases until the fuel pressure reaches a constant pressure, the ball 26 seats on the annular slope 25a. As a result, the residual pressure in the fuel pipe is kept constant, thereby stabilizing the injection.

The reason why the diameter of the second orifice 32 is made smaller than that of the first orifice 31 is to prevent the residual pressure in the fuel pipe from decreasing. After the fuel injection is completed, the reflected wave of the fuel from the injection nozzle is narrowed by the first orifice 31,
The reflected waves enter the expansion chamber 25 and are then narrowed by the second orifice 32, so that the reflected waves are successively reflected by the respective orifices 31 and 32 and propagate to the injection nozzle. Therefore, the secondary wave of fuel heading toward the injection nozzle is attenuated in two stages, and the pressure of the secondary wave is lowered. As a result, the flow rate of fuel flowing toward the plunger chamber between the ball 26 and the annular slope 25a becomes small, and stable injection can be obtained without causing a decrease in the residual pressure of the fuel in the fuel pipe leading to the injection nozzle.

Next, this example will be explained in comparison with a comparative example. In a discharge valve 50 according to a comparative example shown in FIG. 6, an orifice 51 communicating with a through hole 53 is formed at the nozzle side end of a valve body 52. No orifice is formed at the end of the valve body 52 on the plunger side. According to this comparative example, after the end of pressure feeding of fuel to the injection nozzle, the fuel in the fuel pipe passes through the orifice 51 and enters the through hole 53, and when the pressure of the fuel overcomes the set pressure of the compression coil spring 28, the ball 26 open. In this case, in the high-speed rotation range, the ball 26 tries to open excessively against the compression coil spring 28, so the residual pressure in the fuel pipe tends to decrease, which may cause irregular injection.

On the other hand, in this embodiment, after the fuel injection is completed, fuel is introduced into the expansion chamber 25 from the first orifice 31 to prevent secondary injection of fuel, and the fuel enters the expansion chamber 25 from the first orifice 31. The fuel is further throttled through the second orifice 32 to alleviate the attenuation of the fuel, thereby preventing the residual pressure of the fuel from decreasing even in the high speed rotation range and suppressing the occurrence of irregular injection.

Next, FIG. 3 shows the relationship between the pump rotational speed and the residual pressure in the fuel pipe. According to the comparative example, the residual pressure in the fuel pipe decreases in the high speed range of the pump rotation speed, whereas in this example, the residual pressure in the fuel pipe is maintained almost constant from the low speed range to the high speed range. be done. Figure 4
In this example, the diameter of the first orifice 31 is 0.8 mm.
The residual pressure reduction amount in the fuel pipe and the secondary injection generation limit injection amount are shown when the hole diameter of the second orifice 32 is fixed to . In the comparative example, the diameter of the orifice was set to 0.8 mm, and in this case, the residual pressure reduction amount was relatively larger than that of the present example. On the other hand, in the case of this embodiment, the first
By making the hole diameter of the second orifice 32 smaller than the hole diameter of the orifice 31, it is possible to almost eliminate the residual pressure reduction amount without reducing the secondary injection generation limit injection amount so much.

FIG. 5 shows a second embodiment of the present invention. Second
The discharge valve 40 according to the embodiment is an example in which a second orifice 42 is formed in a ring 43 that is press-fitted into a valve body 41. The first orifice 44 is formed at the nozzle side end of the valve body 41. Portions having substantially the same configuration as those in the first embodiment are given the same reference numerals. According to the second embodiment, the valve body 41
By changing the hole diameter of the second orifice formed in the ring 43 with respect to the unique hole diameter of the first orifice formed in the ring 43, there is an effect that prevention of secondary injection occurrence and prevention of irregular injection can be easily adjusted at the same time. .

In the first and second embodiments, the rings 30, 43 and the spring seat 29 are connected to the valve body 22,
41 and the valve case 21 by press-fitting, the fixing means is not limited to this, and may be, for example, screwed in, caulked, or the like. Of course, the first orifice and the second orifice may open directly into the valve body.

[0017]

As explained above, according to the fuel injection pump of the present invention, after the fuel injection operation is completed, the fuel in the fuel pipe is gradually squeezed through the first orifice and the second orifice to escape to the plunger chamber side. Therefore, it is possible to prevent the occurrence of secondary fuel injection, and also to maintain the residual pressure in the fuel pipe at a high pressure even in a high speed rotation range, thereby preventing irregular injection.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a discharge valve according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a fuel injection pump according to an embodiment of the present invention.

FIG. 3 is a characteristic diagram showing the relationship between the pump rotation speed and the residual pressure in the fuel pipe.

FIG. 4 is a characteristic diagram showing the relationship between an example of the present invention and a comparative example, and shows the relationship between the hole diameter of the orifice, the residual pressure reduction amount, and the secondary injection generation limit injection amount.

FIG. 5 is a longitudinal sectional view showing a discharge valve according to a second embodiment of the invention.

FIG. 6 is a longitudinal sectional view showing a discharge valve according to a comparative example.

[Explanation of symbols]

4 Plunger 7 Injection nozzle 10 Plunger chamber 15 Compression coil spring (biasing means) 21 Valve body case 21b Valve seat (annular valve seat) 22 Valve body 22a Large diameter portion 25 Expansion chamber 26 Ball (check valve) 31 First Orifice 32 Second orifice

Claims (1)

[Claims] 1. A fuel injection pump for an internal combustion engine that pressurizes fuel in a plunger chamber and injects it from an injection nozzle through compression motion of a plunger, the valve case having a cylindrical shape through which fuel can flow, the case having an inner circumferential wall at one end thereof. a valve case having an annular valve seat; a valve body reciprocably housed within the valve case and having a large diameter portion that can come into contact with the annular valve seat; a first orifice formed in a passage passing through an end on the plunger chamber side and an end on the injection nozzle side of the valve body; A second orifice is formed in the passage on the plunger chamber side of the first orifice, and a second orifice has a diameter smaller than or equal to the hole diameter of the first orifice, and a second orifice is formed in the passage between the first orifice and the second orifice. It is characterized by comprising: an expansion chamber; and a check valve that is provided in the passage on the plunger chamber side of the second orifice and allows fuel in the passage to flow from the injection nozzle only in the direction toward the plunger chamber. Discharge valve for fuel injection pump of internal combustion engine.