JPH02248645A - Fuel injection pump with pilot injection device - Google Patents

Abstract

PURPOSE:To cool a piezoelectric element laminated body generating high heat without feeding fuel into the recessed part of a piston by forming a ring space between the outer circumferential surface of the boundary part between a first piston part and a second piston part and the cylinder wall surface of a cylinder, and forming a piezoelectric element laminated body and a feed passage for feeding a cooling solution to the ring space. CONSTITUTION:A pilot injection device 1 is formed of a cylinder 11 having a cylinder chamber 11a communicated with a pump chamber 88, a piston 12 sliding in the cylinder, a seal member 13 for sealing the cylinder wall 11b and the piston 12, a piezoelectric element laminated body 14 interposed between the piston 12 and the bottom surface 11b of the cylinder 11, and a feed passage 15 for supplying a cooling solution provided in the cylinder 11. The piezoelectric element laminated body 14 is supported between the bottom part 12a of the piston 12 forming a first piston part 121 and the bottom part 112b of a second cylinder 112. The first cylinder 111 and the second cylinder 112 have the feed passage 15 for feeding fuel to a ring space 12b, and the feed passage 15 is communicated with a feed pipe 151 provided in the second cylinder 112.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel injection pump having a pilot injection device for controlling pilot injection.

[Prior art] Automotive diesel engines are designed to supply fuel pressurized by a fuel injection pump to the engine through an injection nozzle, but in order to reduce noise and vibration during idling, the fuel is It is known that pilot injection is effective.

The pilot injection device controls the pressure of fuel by connecting an actuator to the pump chamber of the fuel injection pump. For example, as disclosed in Japanese Patent Application Laid-Open No. 63-134849, in a distribution type fuel injection pump, while the plunger is pressurizing the fuel in the pump chamber, this fuel is temporarily released by the actuator. If this is done, the fuel pressure in the pump chamber becomes lower than the valve opening pressure of the injection nozzle and injection is temporarily stopped, making pilot injection possible. Specifically, a casing fixed to a pump housing, a pressure chamber formed within the casing and communicating with the pump chamber, a piston slidably disposed within the casing, and a piston housed within the casing and the pressure chamber communicated with the pump chamber. A piezoelectric device comprising a stack of piezoelectric elements that drives a piston is known.

[Problems to be Solved by the Invention] However, in the above structure, there is not only a risk that fuel may flow into the piezoelectric element laminate, causing electrical leakage and malfunction, but also that the piezoelectric element laminate may reach the Curie point. The drawback was that it could get very hot up close.

The present invention was devised in view of the above drawbacks, and a technical problem is to provide a pilot injection device for a fuel injection pump that can cool the piezoelectric element stack without fuel flowing into the piezoelectric element stack. do.

[Means for Solving the Problems] A fuel injection pump having a pilot injection device of the present invention feeds the fuel pressurized by the plunger in the pump chamber to the injection nozzle through the injection passage, and also reduces the pressure of the pressurized fuel. In a fuel injection pump provided with a pilot injection device that performs pilot injection by controlling the fuel injection device, the pilot injection device has one end communicating with the pump chamber, the other end being bottomed, and a first cylinder wall on the one end side, and the other end. A cylinder having a second cylinder wall on an end side, one end side being a first piston part that comes into sliding contact with the first cylinder wall, and the other end side being a second piston part that comes into sliding contact with the second cylinder wall, the first piston. a piston having a concave portion that forms a ring-shaped space between the outer peripheral surface of the boundary portion of the first piston portion and the second piston portion and a cylinder wall surface of the cylinder, and that opens to the other end side;
a seal member that seals the cylinder wall and the second piston portion; a piezoelectric element laminate having one end in contact with the bottom surface of the cylinder and the other end in contact with the bottom surface of the concave portion of the piston; and a piezoelectric element laminate provided in the cylinder and the ring The cooling liquid is characterized by having a supply passage that supplies cooling liquid to the shaped space.

[Operation] With the above configuration, the piston moves within the cylinder due to the expansion and contraction of the piezoelectric element stack, and pilot injection is performed. Here, since a seal member is interposed between the second cylinder wall and the second piston portion, fuel does not flow into the piezoelectric element stack. In addition, the cooling liquid is supplied from the supply passage to the ring-shaped space between the outer peripheral surface of the boundary between the first piston part and the second piston part and the cylinder wall surface of the cylinder, and the pilot injection device including the piezoelectric element stack is supplied with the cooling liquid from the supply passage. Cool the main unit.

[Example] First, an injection pump portion of a distribution type fuel injection pump having a pilot injection device according to this example will be described. In FIG. 2, reference numeral 80 denotes a distribution type fuel injection pump body, and since this distribution type fuel injection pump body 80 is a well-known one, a detailed explanation will be omitted. The face cam 82 in the engine 81 is driven, and the face cam 82 is reciprocated during one rotation according to the number of cylinders of the engine by the same number of cam rollers 83 as the number of cylinders connected to this face cam 82. A plunger 84 connected to the face cam 82 is reciprocated a plurality of times during one rotation depending on the number of cylinders of the engine.

During the suction process of the plunger 84, one of the suction grooves 85 formed on the circumferential surface of the tip of the plunger 84 is inserted into the suction boat 8.
6, the fuel in the fuel chamber 87 is sucked into the pump chamber 88 through the introduction path. During the compression process of the plunger 84, the fuel in the pump chamber 88 was pressurized, and this pressurized fuel was pushed out into the vertical hole 89, and the supply boat 90 communicated with one of the protruding boats 91. In case the injection passage 92
through the fuel injection nozzle 94 via the delivery valve 93.
supplied to

When fuel is being supplied to the fuel injection nozzle 94 through the injection passage 92, the spill boat 96 communicating with the vertical hole 89 is released from the end face of the spill ring 95 provided on the plunger 84 into the fuel chamber, and the inside of the vertical hole 89 is released. Fuel escapes from the spill boat 96 to the fuel chamber 87. This stops the fuel supply to the fuel injection nozzle 94. Therefore, by controlling the movement of the spill ring 95 in the axial direction of the plunger 84, the fuel injection amount can be controlled.

A pilot injection device 1 is attached to the pump housing 81, and the pilot injection device 1 is constructed as shown in FIG.

That is, the pilot injection device 1 includes a cylinder 11 having a cylinder chamber 11a (FIG. 2) that communicates with the pump chamber 88.
, the piston 12 sliding inside the cylinder 11, the sealing member 13 that seals the cylinder wall 111b and the piston 12, the piezoelectric element laminate 14 interposed between the piston 12 and the bottom surface 11b of the cylinder 11, and the cylinder 11. 11 and a supply passage 15 for supplying cooling liquid.

As shown in FIG. 1, the cylinder 11 is formed by screwing together a cylindrical first cylinder 111 and a container-shaped second cylinder 112 having a bottom 112b. The first cylinder 111 has a first cylinder wall 111a with a small diameter on one side of its inner peripheral surface and a second cylinder wall 111b with a large diameter on the other side. As shown in FIG.
It is integrated with 11. The first cylinder 111 and the second cylinder
An O-ring 113 is interposed in the fitting portion of the cylinder 112 for sealing to prevent fuel from flowing in from the outside.

The piston 12 has a cylindrical shape with a bottom and an opening at one end, and has seven ring-shaped portions at the other end.

The side having the bottom portion 12a becomes the first piston portion 121, and the flange-shaped portion at the other end becomes the second piston portion 122. A ring-shaped space 12b is formed between the boundary 123 between the first piston part 121 and the second piston part 122 and the second cylinder wall 111b.A side surface of the first cylinder wall 111a within this space 12b is formed. A spring 16 is interposed between the second piston portion 122 and the side surface of the second piston portion 122, and urges the piston 12 toward the bottom surface 11b of the cylinder 11. First piston part 1
21 opens along the first cylinder wall 111a, and the second piston portion 122 slides along the second cylinder wall 111b. In addition, the second cylinder wall 111b and the second piston portion 12
A sealing member 13 made of an O-ring is interposed between the fuel and the fuel tank 2 to prevent fuel leakage.

Further, a piezoelectric element laminate 14 is sandwiched between the bottom portion 12a of the piston 12 forming the first piston portion 121 and the bottom portion 112b of the second cylinder 112. This piezoelectric element laminate 14 is made by laminating several dozen disk-shaped piezoelectric elements with electrode plates interposed between them, which generate a voltage when a load is applied, and which have the property of causing strain when a voltage is applied.

The end face of this piezoelectric element laminate 14 is kept insulated from other parts by a disc-shaped insulating plate 141. Nao 142
is the lead wire.

Further, the first cylinder 111 and the second cylinder 112 have a supply passage 15 for supplying fuel to the ring-shaped space 12b, and this supply passage 15 communicates with a supply pipe 151 provided in the second cylinder 112.

Furthermore, the first cylinder 111 has a discharge passage (not shown) that discharges fuel from the ring-shaped space 12b.

Next, the operation of this embodiment will be explained.

The distribution type fuel injection pump main body 80 pressurizes the fuel in the pump chamber 88 by the compression action of the plunger 84 . Since the pump chamber 88 and the cylinder chamber 11a are closed by the first cylinder 111 and the piston 12, the pump chamber 88
The fuel in the cylinder chamber 11a is gradually pressurized and sent to the fuel injection nozzle 94 through the vertical hole 89 and the injection passage 92, and the pressure continues to rise until it reaches the valve opening pressure of the fuel injection nozzle 94. At this time, voltage is applied to the piezoelectric element stack 14, causing strain and expansion in the piezoelectric element, so that the volume of the cylinder chamber 11a is reduced.

At this time, the pressure is applied to the tip end surface of the piston 12, and the pressure received by the piston 12 is further applied to the piezoelectric element stack 14 as a load.

22. Since piezoelectric elements have the property of generating voltage when a load is applied, the piezoelectric element laminate 14 expands even when a load is applied.

When this generated voltage is short-circuited at a predetermined timing (when fuel starts to be injected from the injection nozzle), the generated voltage is removed and the strain disappears, so that the piezoelectric element stack 14 instantly contracts.

Then, the volume of the cylinder chamber 11a increases, and the pump chamber 8
When the pressure in the fuel injection nozzle 8 and the cylinder chamber 11a decreases to below the valve opening pressure of the fuel injection nozzle 94, injection is temporarily interrupted.

Then, when the voltage short circuit is released and the plunger 84 continues to pump fuel, the pump chamber 88
Then, the pressure inside the cylinder chamber 11a rises and becomes equal to or higher than the valve opening pressure of the fuel injection nozzle 94, so that injection is restarted. In this manner, pilot injection is performed according to this embodiment.

The state of this pilot injection is shown in Fig. 3. In the figure, a indicates pilot injection, and b indicates main injection. Note that C indicates the case where pilot injection is not performed.

Next, another effect will be shown. Similar to the method described above, the plunger 84
pressurizes the fuel in the pump chamber 88, and the fuel pressure in the pump chamber 88 increases. Then, just before fuel injection starts, a voltage is applied to the piezoelectric element stack 14. As a result, the piezoelectric element laminate 14 is expanded and deformed, and the volume of the cylinder chamber 11a is reduced. That is, the pressure in the pump chamber 88 communicating with the cylinder chamber 11a increases, and fuel is injected. This is pilot injection. Immediately after this, if the voltage applied to the piezoelectric element stack 14 is removed, the fuel pressure in the pump chamber 88 decreases and fuel injection stops. Thereafter, since the plunger 84 continues to pressurize the fuel, main injection is performed when the fuel pressure reaches the valve opening pressure of the fuel injection nozzle 94 again.

Here, the seal member 13 prevents fuel from flowing into the recess that holds the piezoelectric element stack 14 of the piston 12, and fuel is supplied from the supply pipe 151 to the ring-shaped space 12b through the supply passage 15 and via the discharge passage. By discharging the liquid, the main body of the pilot injection device 1 including the piezoelectric element stack 14 can be cooled.

Incidentally, as shown in FIG. 4, the first cylinder wall 111a and the first
The cooling liquid for cooling the piezoelectric element stack 14 by blocking the inflow of fuel from the cylinder chamber 11a into the ring-shaped space 12b through the seal member 17 in the piston portion 121B is not only fuel but also engine cooling water, etc. A large amount of fluid can be used.

[Other Examples] A pilot injection device 2 according to another example includes a cylindrical cylinder 21 having a bottom portion 212, a piston 22 that slides inside the cylinder 21, and an inner peripheral surface 21a of the cylinder 21 and the piston 22. A sealing member 23 for sealing and a piston 2
2 and the bottom surface 21b of the cylinder, a supply passage 25 provided in the cylinder 21 for supplying and discharging cooling liquid, a discharge passage 26, etc.

The inner circumferential surface 21a of the cylinder 21 is a cylindrical surface with no step, unlike the embodiment. Further, the piston 22 is a cylindrical member having a bottom portion 22a, has a first piston portion 221 and a second piston portion 222 having the same diameter on the outer periphery at both ends, and slides on the inner peripheral surface 21a of the cylinder 21. There is a boundary part 223 with a small outer diameter between the first piston part 221 and the second piston part 222, and this boundary part 223 forms a ring-shaped space 22b between the cylinder 21 and the piston 22.

Further, as in the embodiment, the inner circumferential surface 21a of the cylinder 21 and the second
A seal member 23 is interposed between the piston portion 222 and the piston portion 222 .

Bottom 22a of piston 22 and bottom 212 of cylinder 21
A piezoelectric element laminate 24 similar to that of the embodiment is sandwiched between the two and has the same function as that of the embodiment.

Further, the cylindrical portion 211 of the cylinder 21 has a supply passage 25 and a discharge passage 26 that communicate with the ring-shaped space 22b, respectively.
By supplying fuel from the supply passage 25 and discharging it from the discharge passage 26 via the ring-shaped space 22b, the same cooling effect as in the embodiment can be obtained. The piston 22 is connected to the cylinder 21 by a spring (not shown).
is biased toward the bottom 212 of the.

[Effects of the Invention] The pilot injection device of the fuel injection pump of the present invention includes a cylinder having one end communicating with the pump chamber and the other end having a bottom and having a first cylinder wall on one end side and a second cylinder wall on the other end side. One end side becomes a first piston part that comes into sliding contact with the first cylinder wall, and the other end side becomes a second piston part that comes into sliding contact with the second cylinder wall,
a piston that forms a ring-shaped space between the outer circumferential surface of the boundary between the first piston part and the second piston part and the cylinder wall surface of the cylinder and has a concave part that opens on the other end side; a piezoelectric element laminate having one end in contact with the bottom surface of the cylinder and the other end in contact with the bottom surface of the concave portion of the piston; and a piezoelectric element laminate provided in the cylinder and in the ring-shaped space. By having a supply passage for supplying cooling liquid to the piston, fuel will not flow into the recess of the piston having the piezoelectric element stack, and the piezoelectric element stack, which generates high heat, can be cooled.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a pilot injection device according to an embodiment. FIG. 2 is an explanatory diagram of the distribution type fuel injection pump of the embodiment. FIG. 3 is a diagram showing pilot injection. FIG. 4 is a sectional view showing another aspect of the pilot injection device of the embodiment. FIG. 5 is a sectional view showing a pilot injection device of another embodiment. 1.2... Pilot injection device 11.21... Cylinder 12.22... Piston 13.23... Seal member 14.24... Piezoelectric element laminate 15.25... Supply passage 26 ...Discharge passage patent applicant Nippondenso Co., Ltd.

Claims (1)

[Claims] (1) A fuel injection pump equipped with a pilot injection device that 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 pressurized fuel to perform pilot injection. In the above, the pilot injection device includes a cylinder having one end communicating with the pump chamber and the other end having a bottom, a first cylinder wall on the one end side and a second cylinder wall on the other end side, and a cylinder having one end side connected to the first cylinder wall. 1
A first piston part comes into sliding contact with the cylinder wall, and the other end becomes a second piston part which comes into sliding contact with the second cylinder wall,
a piston that forms a ring-shaped space between an outer circumferential surface of a boundary between the first piston portion and the second piston portion and a cylinder wall surface of the cylinder, and has a recess that opens at the other end; a sealing member for sealing two cylinder walls and the second piston portion; a piezoelectric element laminate having one end in contact with the bottom surface of the cylinder and the other end in contact with the bottom surface of the concave portion of the piston; A fuel injection pump having a pilot injection device, characterized in that the fuel injection pump has a supply passage for supplying a cooling liquid to the ring-shaped space.