JPS63134849A - Pilot injection device for fuel injection pump - Google Patents

Abstract

PURPOSE:To prevent fuel from penetrating a piezoelectric element laminated body even after the longterm use of a pilot injection device by providing a relief groove which collects the fuel raiding into a sliding part between a casing and a piston and lets the above-mentioned fuel go into a low pressure fuel part, and a fuel passage. CONSTITUTION:High pressure fuel pressurizedly fed by a plunger 6 penetrates a clearance between the inner periphery 31a of a casing 31 and the outer periphery 41a of a piston 41. The high pressure fuel penetrated the clearance is first collected in a relief groove 42, and flows toward a fuel collecting chamber 36 through a fuel passage 43 when fuel pressure gradually rises to exceed pressure in the fuel collecting chamber 36. The fuel flowed into the fuel collecting chamber 36 is returned to the side of an intake port 8 through a communicating hole 37. Consequently, even when the piston 41 is slided for the longterm use of a pilot injection device, the fuel can never penetrate a piezoelectric element laminated body 45, and the occurrence of leakage due to the penetration of the fuel can be therefore prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pilot injection device that is installed in a fuel injection pump and controls pilot injection using a piezoelectric element stack.

[Conventional technology]

In automotive diesel engines, fuel is pressurized by a fuel injection pump and supplied to the engine through an injection nozzle.
However, the noise during idling,
It is known that pilot injection of fuel is effective in reducing vibration.

As a pilot injection device, an actuator is connected to a pump chamber of a fuel injection pump to control fuel pressure.

For example, in a distribution type fuel injection pump, if the actuator temporarily releases the fuel while the plunger is pressurizing the fuel in the pump chamber, the fuel pressure in the pump chamber will be lower than the opening pressure of the injection nozzle. Since injection is temporarily stopped, pilot injection becomes possible.

In such a pilot injection device, the operational performance of the actuator, that is, the responsiveness is a problem.

In other words, if you want to perform pilot injection when the engine is idling, 1m5ec (l 0-3s e
c) The following responsiveness is required, and an actuator with excellent responsiveness is desired.

That is, the piezoelectric element stack type actuator currently being considered is composed of a cylinder, a piston housed in the cylinder, and a piezoelectric element stack that drives the piston, and a pressure chamber surrounded by the cylinder and the piston. It has a structure that communicates directly with the pump chamber.

With this structure, when the piezoelectric element stack contracts while pressurizing the fuel in the pump chamber with the plunger, it escapes into the pressure chamber.
Since the fuel pressure in the pump chamber becomes lower than the valve opening pressure of the injection nozzle, injection is temporarily stopped and pilot injection becomes possible.

Here, an O-ring is provided at the sliding portion between the cylinder and the piston to prevent fuel from entering the piezoelectric element stack, and the O-ring provides a seal.

[Problem that the invention seeks to solve]

However, in this structure, the piston slides at a stroke of about 0.1+mn and a frequency of about 150Hz, and the fuel pressure inside the pump chamber is extremely high, so even if it is sealed with an O-ring, it will not work for a long time. After use, fuel enters the piezoelectric stack.

On the other hand, piezoelectric element stacks have very high driving voltages, so
Even a small amount of moisture can cause leakage, and as mentioned above, if fuel (hydrated light oil) enters the piezoelectric element stack, there is a fear that it will lead to leakage.

The present invention has been made in view of the above problems.
It is an object of the present invention to provide a pilot injection device for a fuel injection pump in which a piston slides under high fuel pressure and fuel does not enter a piezoelectric element stack even if the piston is used for a long time.

[Means for Solving the Problems] In order to achieve the above object, the present invention takes the following technical measures.

That is, a pilot injection device is provided that pressure-feeds the fuel in the pump chamber pressurized by the plunger to the injection nozzle through the injection passage, and controls the pressure of the fuel pressurized in the pump chamber to perform pilot injection. In the fuel injection pump, the pilot injection device includes a casing fixed to the pump housing, a pressure chamber formed within the casing and communicating with the pump chamber, a piston slidably disposed within the casing, and the casing. a piezoelectric element laminate housed within the casing and driving the piston; a sliding part between the casing and the piston; an annular relief groove formed all around the inner peripheral surface of the casing or the outer peripheral surface of the piston; It is characterized in that it includes a fuel passage that communicates the relief groove with the low-pressure fuel section, and the fuel is recovered from the casing by sliding of the piston and released to the low-pressure fuel section via the fuel passage.

〔Example〕

Next, the present invention will be explained in detail using FIGS. 1 and 2. FIG. 1 is a sectional view showing a pilot injection device of this embodiment, and FIG. 2 is a sectional view showing a distribution type fuel injection pump of this embodiment.

First, the distribution type fuel injection pump of this embodiment will be explained with reference to FIG. In FIG. 2, reference numeral 1 denotes a distribution type fuel injection pump. This distribution type fuel injection pump 1 is a well-known type, so a detailed explanation will be omitted.
The face cam 4 in the engine is driven, and the face cam 4 is moved back and forth according to the number of cylinders of the engine during one revolution by the same number of cam rollers 5 as the number of cylinders in rolling contact with this face cam 4. A plunger 6 connected to a face cam 4 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, the suction groove 7 formed on the circumferential surface of the tip of the plunger 4...
When one of the pumps communicates with the suction port 8, fuel in the fuel chamber 9 is sucked into the pump chamber 11 through the introduction path 10. During the compression stroke of the plunger 6, the fuel in the pump chamber 11 was pressurized, this pressurized fuel was pushed out into the vertical hole 12, and the supply port 13 communicated with one of the plurality of discharge ports 14. In this case, the fuel is supplied to the fuel injection nozzle 17 via the injection passage 15 and the delivery valve 16 .

When fuel is being supplied to the fuel injection nozzle 17 through the injection passage 15, the spill port 1 communicates with the vertical hole 12 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 12 is released to the fuel chamber 9 through the spill port 19. This stops the fuel supply to the fuel injection nozzle 17. 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 operated by the centrifugal force governor 2o and the accelerator-linked lever 21.

Note that the fuel chamber 9 stores fuel sent from the feed pump 22.

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
When the plunger 5 is advanced or retarded, the movement timing of the plunger 6 in the axial direction is changed, thereby controlling the fuel injection timing.

A pilot injection device 30 is attached to the pump housing 3, and this pilot injection device 30 is constructed as shown in FIG.

That is, in FIG. 1, 31 is a casing having a cylinder shape, and this casing 31 constitutes a part of the pump housing 3 and is screwed onto the pump head 26 forming the pump chamber 11. It is kept liquid-tight by sealing materials such as.

An annular protrusion 35 is formed on the front end surface of the casing 31, and a fuel reservoir 36 is formed around the outer periphery of the protrusion 35. This fuel reservoir 36 communicates with the intake port 8 through a communication hole 37. are doing.

The protrusion 35 comes into pressure contact with the end surface 3a of the housing 3 when the casing 31 is screwed onto the pump head 26.
Completely separate the high pressure side and low pressure side.

A piston 41 having a hollow cylindrical shape with a garden is disposed inside the casing 31 . There is a slight clearance (several microns) between the outer peripheral surface 41a of the piston 41 and the inner peripheral surface 31a of the casing 31.
is slidable within the casing 31. Furthermore, the end surface of the bottom surface portion 41c of this piston 41 and the casing 31
A pressure chamber is formed by the inner circumferential surface 31a of the
This pressure chamber 38 communicates with the pump chamber 11.

An annular groove 41d is formed on the outer peripheral surface 41a of the piston 41 over the entire circumference.
A ring 40 is provided.

An annular relief groove 42 is formed all around the inner peripheral surface 31a of the casing 31, which is the sliding part between the casing 31 and the piston 41 and is always located closer to the plunger 6 than the O-ring 40. The relief groove 42 is the fuel passage 4
3 and communicates with the fuel reservoir 36.

A piezoelectric element laminate 45 is housed inside the casing 31 . Although not shown in detail, this piezoelectric element laminate 45 consists of several dozen disc-shaped piezoelectric elements that generate voltage when a load is applied, and which have the property of causing strain when a voltage is applied, with electrode plates interposed between them. It is made of laminated crosspieces.

This piezoelectric element laminate 45 is inserted into an insulating chirp (not shown) to maintain insulation from the outer circumference, and one end surface 45
A is fixed to the bottom surface 41c of the piston 41 while being insulated from other parts by a disc-shaped insulating plate 44 (made of resin, ceramic, etc.). Further, the other end surface 45b of the piezoelectric element laminate 45 is also fixed to the end surface 31b of the casing 31 via the insulating plate 44. In addition,
46 is a lead wire.

Next, the operation of this embodiment will be explained.

The distribution type fuel injection pump 1 pressurizes the fuel in the pump chamber 11 by compressing the plunger 6 .

Since the pump chamber 11 and the pressure chamber 38 are closed by the projection 35 and the piston 41, the fuel in the pump chamber 11 and the pressure chamber 38 is gradually pressurized and flows through the vertical hole 12 and the injection passage 15 to the injection nozzle 17. The pressure continues to rise until it reaches the valve opening pressure of the injection nozzle 17.

At this time, the pressure is applied to the tip end surface 41c of the piston 41, and the pressure received by the piston 41 is further applied to the piezoelectric element stack 45 as a load.

Here, since the piezoelectric element has the property of generating voltage when a load is applied, a voltage is generated in the piezoelectric element stack 45.

This generated voltage is applied at a predetermined timing (injection nozzle 17
When the short circuit occurs at the point when fuel starts to be injected from ), the generated voltage is removed and the piezoelectric element stack 45 instantly
The response time is 100 μsec).

Then, the volume of the pressure chamber 38 increases, and when the pressure in the pump chamber 11 and the pressure chamber 38 decreases to below the opening pressure of the injection nozzle 17, the injection is temporarily interrupted.

However, since the plunger 6 continues to pump fuel, the pressure in the pump chamber 11 and the pressure chamber 38 rises again, and when the pressure reaches the opening pressure of the injection nozzle 17 or higher, injection is restarted. In this way, two-stage injection (pilot injection) is performed according to this embodiment.

In the above operation, when the plunger 6 pressurizes the fuel, a very large pressure is applied to the tip surface 41c of the piston 41. Further, between the inner circumferential surface 31a of the casing 31 and the outer circumferential surface 41a of the piston 41, the piston 41
A clearance of several microns is provided so that the parts can slide freely.

Therefore, high pressure fuel enters into this slight clearance.

The high-pressure fuel that has entered in this way is first collected in the relief groove 42. Then, when the pressure of the fuel stored in the relief groove 42 gradually increases and becomes higher than the pressure in the fuel reservoir 36, the fuel flows through the fuel passage 43 toward the fuel reservoir 36. Note that the fuel reservoir 36 is connected to the pressure chamber 38 by the protrusion 35.
The pressure in the fuel reservoir 36 is always lower than the pressure in the pressure chamber 38.

Further, the fuel that has leaked into the fuel reservoir 36 is removed from the communication hole 37.
is returned to the suction boat 8 side through the suction boat 8.

As described above, according to this embodiment, even if the piston 41 is used for a long period of time while sliding, the fuel that has entered the sliding portion between the inner circumferential surface 31a of the casing 31 and the outer circumferential surface 41a of the piston 41 is The fuel is released to the low pressure side through the relief groove 42 and the fuel passage 43. Therefore, fuel does not enter into the piezoelectric element stack 45, and leakage due to fuel entry can be prevented.

In this embodiment, the relief groove 42 is formed on the inner circumferential surface 31a of the casing 31, but it may be formed on the outer circumferential surface 41a of the piston 41, as shown in FIG. This is because the amount of displacement of the piezoelectric element laminate 45 is several tens of microns, so the stroke of the piston 41 is also about that amount. Therefore, even if the piston 41 slides, the outer peripheral surface 4 of the piston 41
Relief groove 42 formed in 1a and opening 4 of fuel passage 43
3a can always be matched.

Further, as shown in FIG. 1, it is very difficult to drill the fuel passage 43 at a certain angle with respect to the inner circumferential surface 31a of the casing 31 to communicate with the relief groove 42. Therefore, as shown in FIG. 4, a first fuel passage 430 communicating with the relief groove 42 is bored in the radial direction of the casing 31.
A second fuel passage 431 that communicates the fuel passage 430 with the fuel reservoir chamber 36 is bored in the axial direction of the casing 31,
The outer opening 430a of the first fuel passage 430 may be completely blocked by inserting a blind plug 432 into the opening 430a.

Furthermore, as shown in FIG.
2 in the radial direction of the casing 31,
The fuel flowing out through the fuel passage 43 may be returned to the fuel chamber 9 or the fuel tank using a drain hose (not shown) or the like.

[Effects of the Invention] As explained above, according to the present invention, even if the piston is used for a long period of time while sliding, the fuel that has entered the sliding part between the casing and the piston is recovered by the relief groove and the pressure is reduced to a low level. Since it escapes to the side, it does not enter into the piezoelectric element stack 45, and leakage can be prevented.

[Brief explanation of the drawing]

1 and 2 relate to an embodiment of the present invention,
FIG. 1 is an enlarged cross-sectional view of the section ■ in FIG. 2, FIG. 2 is a cross-sectional view showing the distribution type fuel injection pump of this embodiment, and FIG. FIG. 4 is a cross-sectional view of a main part showing a third embodiment of the present invention, and FIG. 5 is a cross-sectional view of a main part showing a fourth embodiment of the present invention. 1...Distribution type fuel injection pump, 6...Plunger 2
11... Pump chamber, 15... Injection passage, 17...
Fuel injection nozzle, 30... Pilot injection device, 31
...Casing, 36...Fuel reservoir chamber (low pressure fuel part), 38...Pressure chamber, 41...Piston, 42...
- Relief groove, 43... fuel passage, 45... piezoelectric element laminate.

Claims (1)

[Claims] (1) A pilot injection device is provided which forces the fuel in the pump chamber pressurized by the plunger to the injection nozzle through the injection passage and controls the pressure of the fuel pressurized in the pump chamber to perform pilot injection. In the fuel injection pump, the pilot injection device includes a casing fixed to the pump housing, a pressure chamber formed within the casing and communicating with the pump chamber, and a piston slidably disposed within the casing. , a piezoelectric element laminate housed in the casing and driving the piston, and a sliding portion between the casing and the piston, which is formed over the entire circumference of the inner peripheral surface of the casing or the outer peripheral surface of the piston. an annular relief groove; and a fuel passage communicating the relief groove with a low-pressure fuel section, and the relief groove collects fuel that has entered the sliding portion between the casing and the piston due to the sliding of the piston. A pilot injection device for a fuel injection pump, characterized in that the fuel is released to a low pressure fuel section via the fuel passage.