JPH0519574Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a cooling control device for a piezoelectric element used for fuel injection control of an internal combustion engine.

[Conventional technology]

Piezoelectric elements have a Curie point, e.g. 150℃
If it exceeds this value, operation will become unstable. Therefore, conventionally, when piezoelectric elements are used for fuel injection control of internal combustion engines, a cooling liquid is guided around the piezoelectric elements so that the piezoelectric elements are constantly cooled by this cooling liquid (Japanese Patent Application Laid-open No. (See Publication No. 19968-1980 or Japanese Patent Application Laid-open No. 104762-1982).

[The problem that the idea aims to solve]

However, since the crystal structure of the piezoelectric element changes depending on the temperature, the amount of charge it can accept changes, and generally speaking, as the temperature of the piezoelectric element decreases, the amount of charge it can accept decreases. As the amount of charge that can be received decreases, the amount of elongation of the piezoelectric element decreases, and therefore, as the temperature of the piezoelectric element decreases, the amount of elongation of the piezoelectric element decreases. Therefore, if the piezoelectric element is constantly cooled by the cooling liquid as described above, the amount of elongation of the piezoelectric element is considerably reduced when the temperature of the piezoelectric element is low, and as a result, there is a problem that fuel injection control cannot be performed.

[Means to solve the problem]

In order to solve the above-mentioned problems, according to the present invention, a cooling liquid flow rate control valve whose flow area increases as the temperature rises is provided in the cooling liquid supply passage for supplying cooling liquid to the piezoelectric element.

〔Example〕

Referring to FIGS. 1, 4, and 5, 1
2 is the housing body, 2 is the nozzle port 3 at its tip.
4 is a spacer, 5 is a sleeve, and 6 is a nozzle holder for fixing the nozzle 2, spacer 4, and sleeve 5 to the housing body 1, respectively. A needle 7 for controlling the opening and closing of the nozzle opening 3 is slidably inserted into the nozzle 2, and the top of the needle 7 is connected to a spring retainer 9 via a pressure pin 8. This spring retainer 9 is constantly pressed downward by a compression spring 10, and this pressing force is transmitted to the needle 7 via the pressure pin 8. Therefore, the needle 7 is always urged in the valve closing direction by the compression spring 10.

On the other hand, a plunger hole 11 is formed coaxially with the needle 7 in the housing body 1, and a plunger 12 is slidably inserted into the plunger hole 11. The upper end of the plunger 12 is a tappet 13
The tappet 13 is always urged upward by a compression spring 14. The tappet 13 is moved up and down by an engine-driven cam (not shown), thereby causing the plunger 12 to move up and down within the plunger hole 11. On the other hand, a fuel pressurizing chamber 15 defined by the plunger 12 is formed in the plunger hole 11 below the plunger 12 . This fuel pressurizing chamber 15 is connected to a needle pressurizing chamber 18 via a rod-shaped filter 16 and a fuel passage 17.
is connected to the nozzle opening 3 via an annular fuel passage 19 around the needle 7. In addition, the plunger hole 11
As shown in Fig. 4, there is a plunger 1 on the inner wall surface of the
2 is in the upper position, a fuel supply port 20 is formed that opens into the fuel pressurization chamber 15, and 3 kg/cm ² flows from this fuel supply port 20 into the fuel pressurization chamber 15.
Fuel is supplied at a certain pressure.

On the other hand, a plunger hole 1 is provided in the housing body 1.
A sliding hole 2 extending laterally near the side in 1.
1 is formed. Inside this sliding hole 21 is an overflow valve 2.
2 is slidably inserted, and adjacent to this sliding hole 21 is a fuel overflow chamber 23 having a larger diameter than this sliding hole 21.
is formed. Fuel is supplied to this fuel overflow chamber 23 from a fuel vicinity port 24, and fuel flows out from a fuel outlet (not shown). The fuel pressure within this fuel overflow chamber 23 is maintained at approximately 3 kg/cm ² . The overflow valve 22 has an enlarged head 22 located within the fuel overflow chamber 23.
a and a circumferential groove 22b formed adjacent to the enlarged head 22a, and the enlarged head 22a controls opening and closing of the valve port 25. The slide valve 22 is always biased toward the right in FIG. 1 by a compression spring 26 located on the opposite side of the enlarged head 22a. Furthermore, as shown in FIG. 4, a fuel overflow passage 27 is formed in the housing body 1, extending radially upward from the fuel pressurizing chamber 15. This fuel overflow path 2
One end of the fuel overflow passage 27 is always in communication with the inside of the fuel pressurizing chamber 15, and the other end of the fuel overflow passage 27 is always in communication with the inside of the circumferential groove 22b of the overflow valve 22.

Furthermore, a rod hole 28 is formed coaxially with the sliding hole 21 in the housing body 1, and the rod hole 28 is formed coaxially with the sliding hole 21.
A rod 29 is slidably inserted within 8. One end of the rod 29 is arranged so as to be able to come into contact with the enlarged head 22a of the overflow valve 22, and a pressure control chamber 30 defined by the other end of the rod 29 is formed at the other end of the rod 29.

On the other hand, a piezoelectric element housing 31 extending vertically upward is fixed to the housing body 1, and a piezoelectric element 32 having a plurality of stacked piezoelectric element plates is inserted into the piezoelectric element housing 31. A piston 33 is slidably inserted into the lower end of the piezoelectric element housing 31, and a cylinder chamber 34 filled with fuel is formed below the piston 33.
This cylinder chamber 34 is connected to the pressure control chamber 30 via a fuel passage 35. In addition, the cylinder chamber 34
A disc spring 36 that always urges the piston 33 upward is inserted therein, and the piezoelectric element 32 is supported between the top of the piezoelectric element housing 31 and the piston 33. The axis of this piezoelectric element 32 is approximately perpendicular to the common axis of the overflow valve 22 and the rod 29, so that the piezoelectric element 32
The axis of the plunger 13 and the needle 7 are substantially parallel to the common axis of the plunger 13 and the needle 7. An annular cooling liquid inlet chamber 37 is formed around the upper end of the piezoelectric element 32 into which a cooling liquid, e.g. fuel, flows, and the cooling liquid inlet chamber 37 is connected to a cooling liquid supply source, e.g. It is connected to the fuel overflow chamber 23 . On the other hand, an annular cooling liquid passage 39 is formed around the piezoelectric element 32 and extends downward from the cooling liquid inlet chamber 37 , and the lower end of this cooling liquid passage 39 is connected to a cooling liquid discharge passage 40 . This cooling liquid discharge passage 40 is open to the atmosphere. The cooling liquid, that is, the fuel that has flowed into the cooling liquid inflow chamber 37 from the fuel overflow chamber 23 via the cooling liquid supply passage 38 cools the piezoelectric element 32 while descending in the cooling liquid flow passage 39, and then the cooling liquid flows down into the cooling liquid flow passage 39. It is discharged from the discharge passage 40.

A plug 41 for supplying power to the piezoelectric element 32 is attached to the top of the piezoelectric element housing 31 .

Referring to FIG. 2, which is an enlarged view of section A in FIG. 1, a cooling liquid flow rate control valve 43 whose flow area increases as the temperature increases is provided in the cooling liquid supply passage 38. This cooling liquid flow control valve 43
is disposed within a sealing member 42 inserted between the housing body 1 and the piezoelectric element housing 31. In the embodiment shown in FIG. 2, this cooling liquid flow rate control valve 43 includes a hollow cylindrical body 44 having a cylindrical hole 44a whose diameter increases as the temperature rises, and a hollow cylindrical body 44 that is inserted into the cylindrical hole 44a. It consists of a hollow cylindrical ball 45 and a hollow cylindrical sealing member 46 fitted onto the outer peripheral surface of the hollow cylindrical body 44. The hollow cylindrical body 44 is made of a material such as copper or polyethylene that has a relatively large coefficient of thermal expansion, and the ball 45
is formed from a material having a smaller coefficient of thermal expansion than the hollow cylindrical body 44. Further, the sealing member 46 is made of a stretchable material such as rubber, and this sealing member 46
When the outer diameter of the hollow cylindrical body 44 changes, the diameter changes accordingly. When the temperature is low, the second
As shown by the broken line B in the figure, the hollow cylindrical body 44 contracts, and the inner circumferential surface of the cylindrical hole 44a of the hollow cylindrical body 44 comes into sealing contact with the outer circumferential surface of the ball 45. Therefore, at this time, the cooling liquid flow rate control valve 43 is completely closed. As the temperature rises, the diameter of the cylindrical hole 44a gradually increases as shown by the solid line, so the area of the flow path formed between the cylindrical hole 44a and the ball 45 gradually increases, and thus the flow is guided to the piezoelectric element 32. The amount of cooling water, that is, the amount of fuel gradually increases.

FIG. 3 shows another embodiment of the cooling liquid flow control valve 43. This embodiment consists of a hollow cylindrical body 47 made of a cooling liquid flow rate alloy and a ball 48 inserted into a cylindrical hole 47a. When the temperature is low, the cylindrical hole 47 is opened as shown by the broken line C in FIG.
The inner circumferential surface of a is in sealing contact with the outer circumferential surface of the ball 48. On the other hand, as the temperature rises, the shape of the hollow cylindrical body 47 changes and the diameter of the cylindrical hole 47a increases as shown by the solid line in FIG.

FIG. 8 shows the relationship between the elongation amount S of the piezoelectric element 32 and the temperature T when the same voltage is applied. It can be seen from FIG. 8 that as the temperature T of the piezoelectric element 32 decreases, the amount of elongation S of the piezoelectric element 32 decreases. By the way, in the present invention, as mentioned above, when the temperature is low, the cooling liquid flow rate control valve 43
is completely closed, and therefore, at this time, the supply of cooling liquid, ie, fuel, to the piezoelectric element 32 is stopped. Moreover, since the cooling liquid passage 39 is arranged vertically, all the fuel in the cooling liquid passage 39 is discharged to the outside through the cooling liquid discharge passage 40, and therefore the inside of the cooling liquid passage 39 is filled with air.
Therefore, since the piezoelectric element 32 is not cooled by the cooling liquid, the amount of elongation S of the piezoelectric element 32 can be prevented from being extremely reduced. On the other hand, when the temperature rises, the piezoelectric element 32
The amount of cooling liquid, ie fuel, introduced to the piezoelectric element 32 is increased, and the piezoelectric element 32 is cooled well, so that the temperature of the piezoelectric element 32 can be prevented from exceeding the Kiuri point. In addition,
As the cooling liquid flow rate control valve 43, other types of control valves, such as a control valve using a bimetal element, can be used, although the structure is somewhat complicated.

On the other hand, as shown in FIGS. 6 and 7, a check valve 50 is inserted into the housing body 1. This check valve 50 includes a ball 52 that controls the opening and closing of the valve port 51, a rod 53 that regulates the lift amount of the ball 52, and a compression spring 54 that constantly presses the ball 52 and rod 53 downward. ,
Valve port 51 is therefore normally closed by ball 52. A valve port 51 of the check valve 50 is connected to the fuel overflow chamber 23 via an annular fuel inflow passage 55 and a fuel inflow passage 56, and a fuel outflow passage 57 of the check valve 50 is connected to the cylinder chamber 34. . As mentioned above, the fuel pressure in the fuel overflow chamber 23 is 3 kg/
^cm2 , and when the fuel pressure in the cylinder chamber 34 becomes lower than the fuel pressure in the fuel overflow chamber 23, the check valve 50 opens and fuel is replenished into the cylinder chamber 34. Therefore, the cylinder chamber 34 is always filled with fuel.

As mentioned above, when the plunger 12 is in the upper position, the fuel pressurizing chamber 1 is supplied from the fuel supply port 20.
Fuel is supplied to the inside of the fuel pressurizing chamber 15, and therefore, at this time, the inside of the fuel pressurizing chamber 15 is at a low pressure of about 3 kg/cm ² . On the other hand, at this time, the piezoelectric element 32 is at the maximum contraction position, and the fuel pressure in the cylinder chamber 34 and pressure control chamber 30 is at a low pressure of about 3 kg/cm ² at this time. Therefore, at this time, the overflow valve 22 is moved to the right in FIG. 1 by the spring force of the compression spring 26, and the enlarged head 22a of the overflow valve 22 opens the valve port 25. Thus, at this time, the fuel pressure within the fuel overflow passage 27 and the circumferential groove 22b of the overflow valve 22 is also at a low pressure of about 3 kg/cm ² .

Next, when the plunger 12 descends, the fuel supply port 20 is closed by the plunger 12, but since the overflow valve 22 opens the valve port 25, the fuel in the fuel pressurizing chamber 15 flows through the fuel overflow path 27, The fuel flows out into the overflow chamber 23 through the circumferential groove 22b of the overflow valve 22 and the valve port 25. Therefore, at this time as well, the fuel pressure in the fuel pressurizing chamber 15 remains at a low pressure of about 3 kg/cm ² .

Next, the piezoelectric element 3 is activated to start fuel injection.
When an electric charge is charged to the piezoelectric element 32
extends in the axial direction, and as a result, the piston 33 descends, so that the cylinder chamber 34 and the pressure control chamber 3
Fuel pressure within 0 rises rapidly. Pressure control chamber 30
As the fuel pressure within the rod 29 increases, the rod 29 moves to the left in FIG.
a closes valve port 25. When the valve port 25 is closed, the fuel pressure in the fuel pressurization chamber 15 increases rapidly due to the downward movement of the plunger 12, and the fuel pressure in the fuel pressurization chamber 15 reaches a predetermined pressure, e.g.
When a certain pressure of 1500 kg/cm ² or more is exceeded, the needle 7 opens and fuel is injected from the nozzle port 3. At this time, high pressure is applied to the circumferential groove 22b of the overflow valve 22 through the fuel overflow passage 27, but since the pressure receiving areas of both axial end faces of the circumferential groove 22b are equal, this high pressure causes the overflow valve 22 to No driving force is applied to the

Next, the piezoelectric element 3 is activated to stop fuel injection.
When the electric charge charged to 2 is discharged, the piezoelectric element 32 contracts. As a result, the piston 33 is raised by the spring force of the disc spring 36, so that the fuel pressure in the cylinder chamber 34 and the pressure control chamber 30 decreases. When the fuel pressure in the pressure control chamber 30 decreases, the rod 29 and the overflow valve 22
The enlarged head 22b of the overflow valve 22 moves to the right in FIG.
opens valve port 25. As a result, the high-pressure fuel in the fuel pressurization chamber 15 flows out into the fuel overflow chamber 23 through the fuel overflow chamber 27, the circumferential groove 22b of the overflow valve 22, and the valve port. The fuel pressure inside 15 immediately drops to a low pressure of about 3.0 Kg/cm ² , and the needle 7 descends to stop fuel injection. Then, the plunger 12 rises, returns to the upper end position, and begins to descend again.

[Effect of idea]

Since it is possible to prevent the piezoelectric element from overheating and to ensure a sufficient amount of elongation of the piezoelectric element when the piezoelectric element is at a low temperature, a good fuel injection action can be ensured at all times.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view of the unit injector taken along the - line in Fig. 4, Fig. 2 is an enlarged side sectional view of section A in Fig. 1, and Fig. 3 is another side sectional view of the cooling liquid flow control valve. Figure 4 is a side cross-sectional view taken along the - line in Figure 1, Figure 5 is a plan view of Figure 1, and Figure 6 is a cross-sectional view taken along the - line in Figure 1. 7 is a sectional view taken along the - line in FIG. 6, and FIG. 8 is a diagram showing the relationship between the amount of elongation of the piezoelectric element and the temperature. 7...Needle, 12...Plunger, 15...
...Fuel pressurization chamber, 21...Sliding hole, 22...Overflow valve, 23...Fuel overflow chamber, 29...Rod, 30
...Pressure control chamber, 32...Piezoelectric element, 38
...Cooling liquid supply passage, 43...Cooling liquid flow rate control valve.

Claims (1)

[Scope of utility model registration request] A cooling control device for a piezoelectric element, in which a cooling liquid flow rate control valve whose flow area increases as the temperature rises is provided in a cooling liquid supply passage that supplies cooling liquid to the piezoelectric element.