JPH051651Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electrostrictive fuel injection valve used in an internal combustion engine.

[Conventional technology]

In a diesel engine, fuel is supplied at high pressure from a fuel injection pump and injected from a fuel injection valve. In this case, the fuel injection pump generates a predetermined high pressure and controls the fuel injection timing, and the fuel injection valve simply opens when high-pressure fuel is supplied. In such conventional fuel injection devices, the fuel injection pump has to be precisely formed, and even then, it has not been possible to inject fuel in a desired pattern, including, for example, pilot injection. In order to obtain a desired pattern of fuel injection, fuel injection valves using electrostrictive actuators have been developed.

JP-A-59-206668 discloses an electrostrictive fuel injection valve that can control opening and closing of a needle valve using an electrostrictive actuator. This electrostrictive fuel injection valve includes a needle inserted into a body having a nozzle opening to open and close the nozzle, and applies fuel pressure to a tapered part of the needle, while applying fuel pressure to the tapered part of the needle. Pressure is applied to the electrostrictive actuator via a hydraulic chamber, and when the electrostrictive actuator retracts, the needle opens the nozzle.

[Problem that the invention attempts to solve]

In the electrostrictive fuel injection valve as described above, fuel is used as operating pressure oil in a hydraulic chamber formed between the end of the needle and the electrostrictive actuator. That is, fuel is supplied from the oil pool in the tapered portion of the needle to the hydraulic chamber on the opposite side of the nozzle through the clearance between the body and the needle. In such a structure, the hydraulic chamber requires hermeticity due to its nature, so it is required to make the clearance as small as possible. On the other hand, since it is necessary to fill the hydraulic chamber with fuel from the oil pool, the clearance is used as a passage. For this purpose, there was a conflicting demand that the clearance must be increased to a certain extent. In reality, the range of clearance that satisfies this requirement is extremely small, and there are problems such as changes in the viscosity of the hydraulic oil, resulting in poor sealing of the hydraulic chamber and poor filling of the hydraulic oil, which impairs injection accuracy. Ta.

[Means for solving problems]

The electrostrictive fuel injection valve according to the present invention includes a needle that is inserted into a body having a nozzle opening to open and close the nozzle opening, applies fuel pressure to a tapered part of the needle, and applies fuel pressure to the opposite side of the needle. In an electrostrictive fuel injection valve, pressure is applied to an electrostrictive actuator through a hydraulic chamber, and when the electrostrictive actuator retracts, the needle opens the nozzle. It is characterized by having a recessed end.

〔Example〕

Referring to FIGS. 1 and 2, the electrostrictive fuel injection valve 10 includes a center body 12, a nozzle body 14 fastened to one end of the center body 12 by a retaining nut 13, and a center body 12. The nozzle body 14 includes an actuator case 16 screwed onto the other end, and a nozzle 18 is formed at the tip of the nozzle body 14. A needle 20 is inserted into the nozzle body 14, and its tip is connected to the nozzle 1.
8 can be opened and closed.

A tapered part 22 is formed in the middle part of the needle 20. Further, a fuel inlet 24 that opens laterally is formed in the center body 12, and this fuel inlet 24 communicates with a fuel passage 26 that is continuously formed in the center body 12 and the nozzle body 14, and this fuel passage 26 is connected to the needle 20. An enlarged annular oil puddle 28 is formed at a position corresponding to the tapered portion 22 of. Therefore, the tapered portion 22 of the needle 20 receives a force in the valve opening direction due to the pressure of the fuel. The fuel inlet 24 is connected to a high-pressure fuel supply device (not shown). This high pressure fuel supply device
Unlike conventional fuel injection pumps, which do not supply high-pressure fuel in a pulsating manner at predetermined times, for example, they consist of a fuel pump and a pressure accumulation chamber, and continuously supply high-pressure fuel at a nearly constant pressure. be.

The center body 12 has a transverse plate wall 30 extending slightly above the needle 20, and a small hydraulic chamber 32 is formed between the lower surface of the transverse plate wall 30 and the upper end surface of the needle 20. This small hydraulic chamber 3
2 communicates with the oil reservoir 28 through a relatively large clearance C formed between the outer periphery of the needle 22 and the inner periphery of the bore of the nozzle body 14. The upper end surface of the needle 20 is formed into a cylindrical recess, and a thin annular rim 34 surrounds the recess 36. Therefore, the small hydraulic chamber 32 includes the inside of this recessed portion 36.

A small hole 38 is provided in the center of the transverse plate wall 30 of the center body 12. center body 12
is formed in a cup shape above the transverse plate wall portion 30, and the actuator case 16 is screwed onto this as described above. Actuator case 16
There is an electrostrictive actuator 4 in which a plurality of thin disk-shaped electrostrictive (piezo) elements are laminated in a cylindrical shape.
0 is housed therein, and is connected to an external power source (not shown) via a lead wire 42. The electrostrictive actuator 40 is held between upper and lower shims 44. The above-mentioned upper cup-shaped portion of the center body 12 forms a cylinder 46,
An actuator piston 48 fitted with a lower shim 44 of the electrostrictive actuator 40 is slidably inserted into this cylinder 46 . A large hydraulic chamber 50 is formed between the lower surface of the actuator piston 48 and the transverse plate wall 30, and this large hydraulic chamber 50 communicates with the small hydraulic chamber 32 via the small hole 38. Further, a disc spring 52 for returning the actuator piston 48 is arranged in the large hydraulic chamber 50, and
A compression spring 54 is disposed between the stepped portion 8 and the recessed portion 36 in order to alleviate an impactful opening of the valve.

Next, the effect will be explained.

At the time of startup, the pressure of the fuel in the oil reservoir 28 is low, and when the electrostrictive actuator 40 is not operating, the pressures in the large hydraulic chamber 50 and the small hydraulic chamber 32 are also low. Therefore, the fuel can enter the large hydraulic chamber 50 and the small hydraulic chamber 32 from the oil reservoir 28 through the relatively large clearance C, and immediately fills the large hydraulic chamber 50 and the small hydraulic chamber 32. However, back pressure can be applied to the needle 20, and abnormal injection does not occur. When the electrostrictive actuator 40 is not operating, the pressure in the large hydraulic chamber 50 and the small hydraulic chamber 32 increases together with the pressure in the oil reservoir 28.

When 500V is applied to the electrostrictive actuator 40,
The electrostrictive actuator 40 extends toward the needle 20 while pushing the actuator piston 48. As a result, the oil pressure of the fuel in the large oil pressure chamber 50 increases, and the oil pressure of the fuel in the large oil pressure chamber 50 is amplified by the area ratio, causing the pressure in the small oil pressure chamber 32 to increase. Therefore, the combination of the large hydraulic chamber 50 and the small hydraulic chamber 32 makes it possible to reliably maintain the needle 20 in the closed state even with the electrostrictive actuator 40 whose displacement is relatively small.

When -200V is applied to the electrostrictive actuator 40, the electrostrictive actuator 40 retracts, and the actuator piston 48 is returned by the disc spring 52 to follow the retracted electrostrictive actuator 40.
Then, the hydraulic pressure in the large hydraulic chamber 50 and the small hydraulic chamber 32, which were applying back pressure to the needle 20, decreases, and the needle 20 rises while pushing the compression spring 54 due to the pressure of the fuel in the oil pool 28, and the nozzle 18 is opened. In this way, the electrostrictive actuator 40 -
The fuel injection valve 10 opens only during the period when 200V is applied, and closes when 500V is applied to the electrostrictive actuator 40. Since the electrostrictive actuator 40 has excellent responsiveness to voltage switching, it is possible to control the opening/closing valve even in a short period of time, and therefore, fuel injection can be controlled in a desired pattern.

As the pressures in the large hydraulic chamber 50 and the small hydraulic chamber 32 change, the thin annular rim 34 around the concave portion 36 at the upper end of the needle 20, which forms a part of the small hydraulic chamber 32, undergoes elastic deformation. This prevents fuel from leaking from the small hydraulic chamber 32. That is, when the electrostrictive actuator 40 expands and the pressure in the small hydraulic chamber 32 increases, the needle 20 opens the nozzle 18 as described above, and the concave portion 3
The thin annular rim 34 around 6 expands outwardly under the pressure of the fuel, resulting in a smaller clearance C. At this time, the pressure in the oil pool 28 is constant and the pressure in the small hydraulic chamber 32 is considerably higher than that, so the fuel in the small hydraulic chamber 32 leaks into the oil pool 28 through the clearance C. If this amount of leakage is large, it will be impossible to maintain the needle 20 in a closed state, and abnormal fuel injection may occur. However, in the present invention, when such leakage is likely to occur, the clearance C is reduced to prevent such leakage, thereby making it possible to reliably maintain the needle 20 in the closed state.

Furthermore, when the electrostrictive actuator 40 is retracted to release the back pressure on the needle 20 and open the needle 20, the pressure in the small hydraulic chamber 32 suddenly decreases, causing the annular rim 34 to deform inward, thereby reducing the clearance. C becomes larger. At this time, when the fuel in the oil pool 28 enters the small hydraulic chamber 32 from the clearance C, the fuel pressure is balanced before and after the needle 20, and the needle 20 closes due to the force of the remaining compression spring 54. A situation may arise where you are forced to do so. However, in this case, when the needle 20 is raised to open the valve, its upper end is seated on the cross plate wall 30 of the center body 12, so fuel does not enter the small hydraulic chamber 32, and therefore the electric power The valve can be kept open until 500V is applied to the strain actuator 40.

[Effect of idea]

As explained above, according to the present invention, since the concave portion is provided at the upper end of the needle opposite to the nozzle, fuel can be reliably filled from the oil pool into the hydraulic chamber, and the pressure in the hydraulic chamber can be prevented from leaking. Therefore, it is possible to obtain a highly accurate fuel injection valve that operates reliably.

[Brief explanation of the drawing]

FIG. 1 is an enlarged view of a main part of FIG. 2 showing an electrostrictive fuel injection valve according to the present invention, and FIG. 2 is a sectional view showing the electrostrictive fuel injection valve according to the present invention. 12... Center body, 14... Nozzle body, 18... Nozzle, 20... Needle, 22...
Tapered portion, 28... Oil pool, 32... Small hydraulic chamber, 36... Recessed portion, 40... Electrostrictive actuator, 48... Piston, 50... Large hydraulic chamber.

Claims (1)

[Scope of utility model registration request] A needle is inserted into a body having a nozzle to open and close the nozzle. Fuel pressure is applied to the tapered part of the needle, and an electrostrictive actuator is connected to the opposite side of the needle via a hydraulic chamber. In an electrostrictive fuel injection valve in which the needle opens the injection port when pressure is applied and the electrostrictive actuator retracts, the end of the needle facing the hydraulic chamber is recessed. Features an electrostrictive fuel injection valve.