JPS6321359A - Accumulate type pilot injection device for fuel injection pump - Google Patents

Abstract

PURPOSE:To obtain a pilot injection device with less variation due to aging effect by forming a projecting part on an accumulate piston and making said projecting part project out into a small hole while creating a throttle passage when said piston is seated on a seat face and reducing the set load of a return spring. CONSTITUTION:Fuel pressure in a pump chamber acts on the projecting part 38 of an accumulate piston 36 toward the small hole 35 of an accumulate cylinder 33, against the pressing force due to the set load of a return spring 43 and, finally, overcomes the pressing force starting to lift up the accumulate piston 36. At this time, since the flow rate of fuel to a seat face 37 is restricted by a throttle passage formed in between the projecting part 38 and the small hole 35, pressure which acts on the seat face 37 is reduced and nearly the projecting part 38 alone is subjected to the fuel pressure. Accordingly, since only the set pressure of the return spring corresponding to the area of the pressure receiving face of the projecting part 38 is required at the time of pilot injection, the set load can be reduced, reducing variation due to aging effect.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is provided in a fuel injection pump, and performs pilot injection from an injection nozzle by controlling the pressure of fuel pressurized in a pump chamber by an accumulation piston. This invention relates to an accumulation type pilot injection device.

[Conventional technology]

In automotive diesel engines, fuel pressurized by a fuel injection pump is supplied to the engine through an injection nozzle, but in order to reduce noise and vibration smoke phenomena during idling, it is necessary to pilot inject the fuel. It is known that it is effective.

As a pilot injection device, rsAE841288
As disclosed in , a fuel injection pump is known in which an accumulator is connected to the pump chamber of the fuel injection pump to control the fuel pressure.

The above-mentioned accumulation type pilot injection device connects an accumulation cylinder through a small hole to a fuel pump chamber pressurized by a plunger of a distribution type fuel injection pump, for example, and slides an accumulation piston into the accumulation cylinder. It is provided with a return spring that can be accommodated freely and presses the accumulation piston.

In this case, when the fuel pressure in the pump chamber is low, the accumulate piston, which is receiving the pressing force of the return spring, is seated and closes the small hole, and the fuel pressure in the pump chamber is reduced by the return spring. When the set load of
Pilot injection is performed by temporarily stopping the injection from the injection nozzle.

In such a pilot injection device, its pilot injection characteristics change depending on the set load of the return spring. That is, as shown in Fig. 8, when the set load of the return spring is large, the pilot injection amount increases as shown by characteristic a, and when the set load of the return spring is small, the pilot injection amount increases as shown in the characteristic already shown. The quantity will be less.

[Problem that the invention seeks to solve]

In the conventional case, the moment the accumulate piston is lifted from the seated state, the high fuel pressure of the pump chamber is applied to the entire surface of the piston's tip surface, so the return spring is forced to move from the pump chamber side. A large set load was required to keep the accumulate piston from lifting below a given fuel pressure.

However, if the set load of the return spring is large, the load on the spring becomes large and it is likely to become sagging, resulting in significant changes in the spring characteristics over time.

For this reason, the pilot injection characteristics change significantly even with a slight change in the return spring over time, resulting in a problem that stable characteristics cannot be maintained.

Therefore, the present invention aims to provide an accumulation type pilot injection device for a fuel injection pump that can reduce the set load of the return spring and reduce the change over time of the return spring.

[Means for solving problems]

The present invention provides an accumulation piston with a protrusion that protrudes into a small hole when the seat surface of the accumulator piston is seated, and a protrusion that protrudes into a small hole when this protrusion is located in the small hole. A constricted passage is formed between the side surface of the protrusion and the inner surface of the small hole.

[Effect]

According to such a configuration, when the fuel pressure in the pump chamber exceeds the set load of the return spring, the accumulate piston starts to lift, but a protrusion is formed at the tip of the accumulate piston, and the side surface of this protrusion Since there is a throttle passage between the inner surface of the small hole and the above-mentioned small hole, the protruding part is pressurized before the seat part of the accumulate piston, and the pressure receiving area of the protruding part is the pressure receiving area of the entire surface of the accumulate piston. Since it is smaller than the area, the set load of the return spring can be reduced.

If the set load of the return spring is reduced, the load on the spring is also reduced and it is less likely to become sagging, thereby reducing changes in spring characteristics over time. Therefore, the pilot injection characteristics do not change due to changes in the return spring over time, and stable characteristics can be maintained over a long period of time.

Note that unless a throttle passage is provided between the side surface of the protrusion and the inner surface of the small hole, the initial purpose of forming the protrusion to reduce the pressure-receiving area will not be achieved.

The explanation will be based on the first embodiment.

In this embodiment, an accumulation type pilot injection device 30 is installed in a distribution type fuel injection pump 1, and the entire distribution type fuel injection pump is shown in FIG. 4, and will be explained first.

That is, ① is a distribution type fuel injection pump, and since this distribution type fuel injection pump 1 is well-known, a detailed explanation will be omitted. face cam 4
is driven, and this face cam 4 is moved back and forth according to the number of cylinders of the engine during one rotation by cam rollers 5 of the same number as the number of cylinders in rolling contact with this face cam 4, and is also connected to this face cam 4. The plunger 6 is reciprocated a plurality of times during one rotation according to the number of cylinders of the engine. During the suction stroke of the plunger 6, when one of the suction grooves 7 formed on the peripheral surface of the tip end of the plunger 6 communicates with the suction port 8, the fuel in the fuel chamber 9 flows through the suction port 8 into the pump chamber. 1o is inhaled. During the compression stroke of the plunger 6, the fuel in the pump chamber 10 was pressurized, this pressurized fuel was pushed out into the vertical hole 11, and the supply port 12 communicated with one of the plurality of discharge ports 13. In this case, the fuel injection nozzle 1 is supplied from the delivery valve 15 through the injection passage 14.
6.

When fuel is being supplied to the fuel injection nozzle 16 through the injection passage 14, the spill port 1 communicates with the vertical hole 11 from the end face of the spill ring 18 provided on the plunger 6.
9 is opened to the fuel chamber 9, and the fuel in the vertical hole 11 is released to the fuel chamber 9 through the spill port 19.

This stops the fuel supply to the fuel injection nozzle 16. Therefore, by controlling the movement of the spill ring 18 in the axial direction of the plunger 6, the fuel injection amount can be controlled.

The spill ring 18 is actuated by a centrifugal force governor 20 and an accelerator interlock lever 21.

Note that fuel sent from the feed pump 22 is stored in the fuel chamber 9.

The fuel in the fuel chamber 9 is introduced into the timer cylinder 23,
By operating the timer piston 24 with this fuel pressure, the roller ring 2 holding the plurality of cam rollers 5
5 is advanced or retarded, the timing of movement of the plunger 6 in the axial direction is changed, thereby controlling the fuel injection timing.

An accumulation type pilot injection device 30 is attached to the pump head 27 which constitutes a part of the pump housing 3 and forms the pump chamber 11 in the distribution type fuel injection pump l having such a configuration.

An accumulating pilot injector 30 is shown in FIGS. 1-3 and will be described below.

That is, 31 is a casing of the pilot injection device 30, and this casing 31 is screwed onto the pump head 27 in a fluid-tight manner.

A partition wall 32 is provided in the middle of the casing 31 in the axial direction, and an accumulation cylinder 33 and a piston stopper 34 are fitted into one of the chambers partitioned by the partition wall 32.

The accumulation cylinder 33 is connected to the pump chamber 10 of the fuel injection pump 1 through a small hole 35, and an accumulation piston 36 is slidably accommodated in the accumulation cylinder 33.

The accumulation piston 36 has a conical Y shape at its tip, for example.
It has a seat surface 37 and a protrusion 38 on the center line. This protrusion 38 is configured to enter into the small hole 35 when the seat surface 37 is seated on the valve seat 39, and the pressure receiving area S at the tip of the protrusion 38 is
2 is naturally smaller than the pressure receiving area S1 of the conical seat surface 37 of the accumulating piston 36 (s2<sl
) is formed.

When the protruding part 38 enters the small hole 35, the gap formed between the outer surface of the protruding part 38 and the inner surface of the small hole 35 forms a throttle passage 40 that acts to reduce pressure.
It is said that

Further, the amount by which the protruding portion 38 enters into the small hole 35 is determined by the amount of the accumulating piston 36 or the piston stopper 34.
The amount of movement until it hits the piston and stops, is smaller than the piston stroke no. 1 (i2<, 121
) has been set.

Note that 41 is a fuel reservoir.

A pressure rod 42 is protruded from the rear end of the accumulation piston 36, and this pressure rod 42 loosely passes through the piston stopper 34 and the partition wall 32 to open the other room partitioned by the partition wall 32. is prominent. In the other room there is a return spring 43.
This return spring 43 presses the pressure rod 42 through the seat 44, and the accumulation piston 3B is thereby pushed against its seat surface 37.
is seated on the valve seat 39.

The rear end of the return spring 43 is in contact with a spring pressing member 45, and this spring pressing member 45 is pressed against the casing 31.
are screwed together. Casing 31 of spring holding member 45
It is possible to adjust the set load of the return spring 43 by adjusting the screwing position. Note that 46 is a lock nut, and 47 is an O-ring.

A fuel relief passage 48 is formed in the spring pressing member 45, and this fuel relief passage 48 is connected to a fuel tank or fuel chamber 9, although not shown.

The operation of the embodiment having such a configuration will be explained.

As mentioned above, the distribution type fuel injection pump 1 pressurizes the fuel in the pump chamber 1 by the compression operation of the plunger 6, pushes out the pressurized fuel into the vertical hole 11, and injects it from the injection passage 4. The fuel is supplied to the fuel injection nozzle 16. When the fuel pressure in the pump chamber 10 becomes higher than the valve opening pressure of the fuel injection nozzle 16, the injection nozzle 1G starts injecting fuel into the combustion chamber (not shown) of the engine.

When the fuel pressure in the pump chamber IO increases, the return spring 4
When the load becomes higher than the set load of No. 3, this pressure acts on the tip of the protrusion 38 that is pushed onto the accumulating piston 36 through the small hole 35, so the accumulating piston 36 resists the pressing force of the return spring 43. and starts moving to the right in FIGS. 1 and 2.

At this time, the protrusion 38 formed at the tip of the accumulate piston 36 has entered the small hole 35, and the protrusion 38 has entered the small hole 35.
8 and the small hole 35 restricts the flow of fuel flowing toward the seat surface 37, so that the pressure acting on the seat surface 37 is reduced. Therefore, the accumulation piston 36 receives fuel pressure only at the tip end surface of the protrusion 38 . Since the pressure receiving area S2 of the protrusion 38 is smaller than the pressure receiving area S1 of the conical seat surface 37 of the accumulating piston 36 (s2<sl), the pressing force from the pump chamber 10 side acting on the accumulating piston 3G is: It is smaller than the conventional case in which the protrusion 38 is not provided.

Therefore, the set load of the return spring 43 is sufficient to resist the fuel pressure acting on the tip pressure receiving area S2 of the protrusion 38, and this set load can be reduced.

As the fuel pressure in the pump chamber 10 continues to increase, the accumulation piston 36 continues to move to the right in FIGS. 1 and 2 against the pressing force of the return spring 43, and the stroke of the accumulation piston 36 increases. If it exceeds 12, the protrusion 38 will come out of the small hole 35, and the throttling effect of the throttling passage 40 will disappear. Therefore, fuel flows into the fuel reservoir 41 from the pump chamber IO side through the small hole 35, and the volume of the pump chamber 10 is substantially increased.

Therefore, at this point, the fuel pressure in the pump chamber 10 decreases and becomes equal to or lower than the valve opening pressure of the injection nozzle 16, so that injection from the injection nozzle 16 is stopped. Therefore, pilot injection is performed (end of pilot injection).

When the accumulation piston 36 hits the piston stopper 34 and stops, the fuel pressure in the pump chamber 10 that is being pressed by the advancement of the plunger 6 rises again, and when it exceeds the valve opening pressure of the injection nozzle 16, the injection nozzle 16 is opened again. Injection is made from. As a result, main injection is performed.

When the end surface of the spill ring 18 opens the spill port 19 and releases the fuel in the pump chamber IO from the spill port 19 to the fuel chamber 9, the fuel pressure in the pump chamber 10 decreases, and therefore the accumulation piston 36 is moved by the return spring. 43 and returns to the left, the seat surface 37 seats on the valve seat 39 and stops. Then, when the fuel pressure in the pump chamber 10 becomes equal to or lower than the valve opening pressure of the injection nozzle 16, injection from the injection nozzle 1B is stopped, thereby ending the main injection.

The fuel relief passage 48 formed in the spring pressing member 45 is for returning fuel leaked from the fuel reservoir 41 through the gap between the accumulation cylinder 33 and the accumulation piston 36 to the fuel tank or fuel chamber 9. .

According to such an embodiment, the set load of the return spring 43 is sufficient to resist the fuel pressure acting on the pressure receiving area s2 of the protrusion 38 formed at the tip of the accumulating piston 36. Since the spring can be made smaller, the load on the spring is reduced, and it is less likely to sag, reducing changes in spring characteristics over time. As a result, changes over time in the pilot injection characteristics are also reduced, and stable characteristics can be maintained over a long period of time.

In addition, since the set load of the return spring 43 can be reduced, a spring with a small spring constant can be used, and the allowable range in which the pilot injection amount can be changed becomes larger. The range of change can be reduced. This makes it easy to fine-tune the optimum pilot injection characteristics, and there are also secondary advantages such as a wider allowable range of the pilot injection characteristics with respect to variations in the valve opening pressure of the injection nozzle.

FIG. 5 shows the relationship between the set load of the return spring 43 and the passage area of the throttle passage 40. Aperture passage 40
If the passage area of Spring 43
The set load can be reduced. On the other hand,
If a gap with a large passage area is created between the protrusion 38 and the small hole 35, the throttling effect will not work, and the entire surface of the accumulating piston 36, including the seat surface 37, will receive pressure, so the set load of the return spring 43 will be increased. must be set. Therefore, according to the present invention, it is possible to use a smaller set load than before.

Note that the present invention is not limited to the first embodiment described above, and may be implemented as a second embodiment shown in FIGS. 6 and 7.

That is, in the second embodiment, the small hole 35 is divided into a small diameter part 51 on the same side of the pump chamber and a large diameter part 52 on the side of the accumulate piston 36, and the protruding part 53 is slidably inserted into the small diameter part 51. By providing grooves along the axial direction on the side surface of the protruding portion 53, the constriction passages 54 and 54 are formed by wave grooves.

The small hole 35 is formed by dividing the cylinder member into a small diameter part 51 and a large diameter part 52, and the reason why the cylinder member is divided 55 and 58 is to center the small diameter part 51 and the protruding part 53. This is to make it easier.

[Effects of the Invention] As explained above, according to the present invention, the set load of the return spring can be reduced, the load on the spring is reduced, and fatigue is less likely to occur, so that changes in spring characteristics over time are reduced. Ru. Therefore, the pilot injection characteristics do not change due to the aging of the return spring, and stable characteristics can be maintained over a long period of time.

[Brief explanation of the drawing]

1 to 5 show one embodiment of the present invention, in which FIG. 1 is a sectional view of an accumulation type pilot injection device, and FIG.
The figure is an enlarged view of the main parts, Figure 3 is a view taken along the line ■-■ in Figure 2, Figure 4 is a sectional view of the entire distribution type fuel injection pump, Figure 5 is a characteristic diagram, Figure 6 and FIG. 7 shows a second embodiment of the present invention, FIG. 6 is an enlarged view of the main part, and FIG.
8 is a characteristic diagram showing pilot injection characteristics. ■...distribution type fuel injection pump, 6...plunger,
10... Pump chamber, 14... Injection passage, 16...
Fuel injection nozzle, 30... Pilot injection device, 31
...Casing, 33...Accumulate cylinder,
35...Small hole, 36...Accumulate piston,
37... Seat surface, 38... Projection part, 39... Valve seat, 40... Restriction passage, 43... Return spring, 51... Small diameter part, 52... Large diameter part , 53... protrusion, 54, 54... throttle passage. 18 Kaisho 63-21359 (7) Figure 5

Claims (2)

[Claims] (1) The fuel pressurized by the plunger in the pump chamber is fed through the injection passage to the injection nozzle, and the pressure of the fuel pressurized in the pump chamber is controlled by an accumulation type pilot injection device to cause the injection nozzle to flow into the injection nozzle. This is a fuel injection pump that performs pilot injection from the fuel injection pump, and the accumulation type pilot injection device has a small hole that communicates between the pump chamber and the inside of the accumulation cylinder, and a pressing force of a return spring housed in the accumulation cylinder. an accumulating piston that opens and closes the small hole in response to the accumulating piston; An accumulation type pilot injection of a fuel injection device, characterized in that when the protrusion is located in the small hole, a throttle passage is formed between the side surface of the protrusion and the inner surface of the small hole. Device. (2) The accumulation type pilot injection device for a fuel injection device according to claim 1, wherein the amount by which the protrusion portion protrudes into the small hole is smaller than the stroke of the accumulation piston.