Injector for internal-combustion engines

Abstract

 An injector for internal-combustion engines, comprising: a base body (12) having a valve seat (20); a needle element (22) which can slide inside the base body (12) and is designed to open and close the aforesaid valve seat; and an actuator device which is designed to control sliding of said needle element (22). The piezoelectric actuator (28) is an amplified piezoelectric actuator having a bar (30) made of piezoelectric material, which co-operates with an amplifying structure (32). The bar (30) of piezoelectric material is set orthogonally to the direction of sliding of said needle element (22).

Description

[0001] The present invention relates to an injector for internal-combustion engines, in particular for petrol engines and diesel engines for motor vehicles.

[0002] More precisely, the invention regards an injector of the type comprising:

• a base body having a valve seat;
• a needle element which can slide inside the base body and is designed to open and close the aforesaid valve seat; and
• an actuator device including a bar made of piezoelectric material, which is designed to control sliding of said needle element.

[0003] In injectors of the more traditional type, the actuator device consists of an electromagnet, which, when excited, generates a force that recalls the needle element towards the inside of the base body, towards a position of opening of the valve seat.

[0004] Also known are injectors in which the actuator device comprises a bar made of piezoelectric material set parallel to the direction of sliding of the needle element. In this solution, when the piezoelectric actuator is activated, it applies a force to the needle element, which tends to push the latter towards the outside of the base body, against the action of elastic means that tend to recall the needle element towards the inside of the base body into a position in which a widened head of the needle element closes the valve seat.

[0005] The injectors provided with piezoelectric-type actuator devices present the advantage of being able to operate with higher fluid pressures, as compared to injectors provided with electromagnetic actuator devices. Typically, injectors for petrol-driven engines with electromagnetic actuators can operate with a fluid pressure of up to 120 bar, whereas injectors with piezoelectric actuators can operate with a fluid pressure of up to 300 bar.

[0006] However, as compared to injectors with electromagnetic actuators, the injectors with piezoelectric actuators of the known type have larger overall dimensions and higher costs, a poorer quality of the jet of fluid, and present more problems as regards the mechanical connection (interface) between the actuator device and the needle element.

[0007] The present invention sets itself the aim of providing an injector of the type specified at the beginning of the present invention, that makes it possible to overcome the aforesaid drawbacks.

[0008] According to the present invention, the said purpose is achieved by providing an injector having the characteristics specified in the main claim.

[0009] The present invention will now be described in detail with reference to the attached drawings, which are provided purely to furnish a non-limiting example, and in which:

Figure 1 is a schematic axial sectional view of an injector for petrol-driven engines, according to the present invention; and

Figure 2 is a schematic axial sectional view of an injector for diesel engines, according to the present invention.

[0010] With reference to Figure 1, the number 10 designates an injector for petrol-driven engines, comprising a base body 12 having a cavity 14, into which, in use, petrol under pressure is fed by means of an inlet connection designed to be connected to a fuel-supply pipe (not illustrated). The base body 12 has a tubular end 18 in which a valve seat 20 communicating with an injection hole is made.

[0011] A needle element 22 is mounted in such a way that it is can slide inside the base body 12 in the direction of its own longitudinal axis 24. A helical spring in compression 26 pushes the needle element 22 towards a position of closing of the valve seat 20.

[0012] The injector 20 according to the present invention comprises an amplified piezoelectric actuator 28 connected to the needle element 22. The amplified piezoelectric actuator 28 is in itself known and may be, for example, of the type manufactured by the company CEDRAD RICERCHE, distinguished by the code APA, Series S or Series M. The actuator device comprises a bar 30 made of piezoelectric material, which extends in a direction orthogonal to the axis 24 of the needle element 22. The bar 30 made of piezoelectric material co-operates with an amplifying structure 32 having two connection points 34, 36 set in line along the axis 24. The connection point 34 has the function of fixing the amplifying structure 32 to the base body 12, and the connection point 36 has the function of connecting the amplifying structure 32 to the needle element 22. An electrical connector 38 electrically connects the bar 30 of piezoelectric material to a conventional-type control unit.

[0013] When the bar 30 of piezoelectric material is deenergized, the actuator 28 is in a resting condition, and the needle element 22 is in a position in which it closes the valve seat 20, the spring 26 having a small load, sufficient for recovery of ?play. When the bar 30 of piezoelectric material undergoes electrical excitation, it dilates in the direction of its own longitudinal axis and deforms the amplifying structure 32. As a result of this deformation, the structure 32 applies a force on the needle element 22 in the direction indicated by the arrow 40 in Figure 1. This force causes a displacement of the needle element 22 against the action of the spring 26, towards a position of opening of the valve seat 20. The amplified piezoelectric actuator device 28 presents all the advantages intrinsic in piezoelectric technology, among which displacement proportional to the electric voltage applied, fast response times, and small power consumption. The actuator 28 is moreover less costly and cumbersome than direct piezoelectric actuators. For example, an amplified piezoelectric actuator 28 having dimensions 2 cm x 1 cm has a stroke of 50 µm and applies a force of 50 N, whilst a direct piezoelectric actuator of equal performance would have overall dimensions of approximately 60-90 mm.

[0014] The amplified piezoelectric actuator 28 enables a needle actuator to be used of a type identical to the one present in injectors with electromagnetic-type actuator devices, in which the needle element is recalled towards the inside of the base body 12 by the force produced by the actuator device. This makes it possible to achieve a jet quality that is typical of electromagnetic injectors, that is, a jet quality that is superior to the one achievable with injectors provided with direct piezoelectric actuators.

[0015] As is illustrated in Figure 2, the present invention may be applied also to injectors for diesel engines. In Figure 2, the items corresponding to the ones previously described are designated by the same reference numbers. Injectors for diesel fuel work at pressures decidedly higher than those of injectors for petrol (for example, of the order of 1500 bar). In this case, as is well known in the sector, the needle element 22 does not control opening of the injection hole directly, but opens a control valve 40. As a result of opening of the control valve 40, a rod 42 slides upwards, opening an injection hole 44, in a way in itself known. In the variant of Figure 2, the needle element 22 is made in a monolithic way (for example co-moulded) with the amplifying structure 32 of the piezoelectric actuator 28.

[0016] Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what is described and illustrated herein, without thereby departing from the scope of the present invention as defined in the ensuing claims.

Claims

1. An injector for internal-combustion engines, comprising:

- a base body (12) having a valve seat (20; 40);

- a needle element (22) which can slide inside the base body (12) and is designed to open and close the aforesaid valve seat; and

- an actuator device including a bar made of piezoelectric material, which is designed to control sliding of said needle element (22),

   characterized in that the aforesaid piezoelectric actuator (28) is an amplified piezoelectric actuator having a bar (30) made of piezoelectric material, which co-operates with an amplifying structure (32), said bar (30) of piezoelectric material being set orthogonally to the direction of sliding of said needle element (22).

2. An injector according to Claim 1, characterized in that the aforesaid needle element (22) is directly fixed to the amplifying structure (32) of the piezoelectric actuator (28).
The foregoing substantially as described and illustrated and for the purposes herein specified.

Drawing