WO2010136655A1

WO2010136655A1 - Fuel injector valve

Info

Publication number: WO2010136655A1
Application number: PCT/FI2010/050435
Authority: WO
Inventors: William Brace; Pekka Hautala; Jukka KIIJÄRVI; Markus Niemi
Original assignee: Wartsila Finland Oy
Current assignee: Wartsila Finland Oy
Priority date: 2009-05-28
Filing date: 2010-05-28
Publication date: 2010-12-02
Anticipated expiration: 2011-11-28
Also published as: FI20095596A0; FI122437B; FI20095596L

Abstract

A fuel injector valve (1) of a piston engine, which comprises a fuel chamber (3) for the fuel to be injected, a valve needle (9) for guiding the fuel injection from the fuel chamber (3) into the cylinder (4) of the engine, and a piezoelectric actuator (11) for guiding the valve needle (9). The valve needle (9) is attached directly to the piezoelectric actuator (11).

Description

FUEL INJECTOR VALVE

This invention relates to a fuel injector valve of a piston engine.

In diesel engines, the fuel is injected as a fine mist from the fuel injector valve into the combustion space of the cylinder such that with eddies of air is achieved a good mixture of fuel and combustion air and combustion that is as perfect as possible. Fuel injected by the injector valve as tiny droplets vaporizes quickly as combustion begins after a short ignition delay. A spring-loaded valve needle is ordinarily used as a shut-off element in an injector valve, which valve needle is generally guided hydraulically by the pressure of the fuel or other hydraulic fluid.

Due to ever more stringent emissions regulations, the emissions created by pis- ton engines must be decreased. It is, however, at the same time desired that the performance of the engine be kept at the same level or even improved. One means of achieving these goals is to adjust with greater accuracy the amount of fuel injection and the timing and duration of injection during the injection event. The accuracy of adjustment of fuel injection can be improved by guiding the valve needle of the injector valve using a piezoelectric actuator. Typically, an injector valve equipped with a piezoelectric actuator comprises a hydraulic or mechanical motion amplifier, with which the motion of the actuator is amplified prior to its transmission to the valve needle. The motion amplifier makes the structure of the valve needle complex and may weaken the accuracy of adjust- ment of the fuel injection.

The object of the invention is to provide a fuel injector valve with a simple structure, which is equipped with a piezoelectric actuator.

The object of the invention is achieved by the injector valve described in claim 1. The injector valve according to the invention comprises a fuel chamber for the fuel to be injected, a valve needle for guiding the injection from the fuel chamber into the combustion space of the cylinder and a piezoelectric actuator for guiding the valve needle. The valve needle is attached directly to the piezoelectric actuator.

With the invention, significant advantages are achieved.

In an injector valve according to the invention, the amount of fuel injection and the timing and duration of injection can be adjusted during the injection event with great accuracy and speed, thus reducing engine emissions and increasing the power of the engine. Because the valve needle is attached directly to the piezoelectric actuator, the motion produced by the actuator i.e. the change in length of the actuator, is transmitted directly to the valve needle. Thus, there is no need within the injector valve for a hydraulic circuit or other arrangement, with which the magnitude and/or strength of the motion of the piezoelectric actuator is amplified prior to transfer to the valve needle. Due to this, the structure of the injector valve can be kept simple. Additionally, an injector valve directly guided by a piezoelectric actuator is fast and reliable.

In the following, the invention is described in greater detail by means of examples and with reference to the accompanying drawings.

Fig. 1 shows as a cross-section a fuel injector valve according to the invention.

Fig. 2 shows as a cross-section a piezoelectric actuator, which can be used in the injector valve of Fig. 1.

Fig. 3 shows as a cross-section another piezoelectric actuator, which can be used in the injector valve of Fig. 1.

In Fig. 1 , there is shown an injector valve 1 for injecting fuel into the combustion space 4 of a cylinder of a piston engine. The injector valve 1 can be installed in connection with the cylinder head of the engine. The injector valve 1 comprises a body 2, which has a fuel chamber 3 for the fuel to be injected into the combustion space 4. The fuel chamber 3 is in the flow connection with the fuel source through the fuel duct 5 in the body 2. The fuel source is, for example, a pressure accumulator or so-called common rail, into which fuel is fed at high pressure and from which fuel is led to one or more injector valves. The body 2 has nozzle openings 7, through which fuel is injected from the fuel chamber 3 into the combustion space 4. The injector valve 1 comprises a valve needle 9 that extends into the fuel chamber 3 and with which the injection of fuel is guided from the fuel chamber 3 into the combustion space 4. The fuel chamber 3 has a seat surface 8, against which the valve needle 9 is pressed by a spring 10. The spring 10 is fitted between the body 2 and the supporting surface 6 of the valve needle.

The injector valve 1 comprises a piezoelectric actuator 11 for guiding the valve needle 9 i.e. for moving it between the open and closed positions. In the closed position, the valve needle 9 is against the seat surface 8 and thus prevents the flow of fuel from the fuel chamber 3 into the combustion space 4. The valve needle 9 is pressed towards the closed position by a spring 10. In the open position, the valve needle 9 is lifted from the seat surface 8, whereby fuel is allowed to flow between the seat surface 8 and the valve needle 9 into the combustion space 4.

The function of the piezoelectric actuator 11 is based on the piezoelectric phenomenon. The actuator 11 comprises piezo elements 12 made of a piezoelectric material, the length of which piezo elements 12 changes in response to an electrical field. The piezo elements 12 comprise piezo crystals, which are ordi- narily made from PZT ceramics, which comprise lead, zirconium and titanium.

The valve needle 9 is attached directly to the piezoelectric actuator 11. Then, the motion produced by the actuator 11 is transmitted directly and as the same magnitude to the valve needle 9. The valve needle 9 is directly guided by the piezoelectric actuator 11. The injector valve 1 does not comprise a hydraulic, mechanical or other motion amplifier, with which the magnitude or strength of the motion produced by the actuator 11 is changed prior to transmission to the valve needle 9. Fig. 2 shows a telescopic piezoelectric actuator 11 , which can be used in the injector valve of Fig. 1. The actuator 11 comprises piezo elements 12, which are fitted within each other. The piezo elements 12 are cylindrical. The piezo ele- ments 12 are arranged to move telescopically in relation to one another, when a voltage is switched to the actuator 11. The ends of adjacent piezo elements 12 are coupled to one another by end connectors 13. Each piezo element 12 is coupled by an end connector 13 from at least one of its ends to the corresponding side end of an adjacent i.e. an inner or outer, piezo element 12. Except for the innermost and outermost piezo elements 12, the first and second end of each piezo element is coupled by an end connector 13 to the corresponding side end of the adjacent, inner or outer, piezo element. The second end of the outermost piezo element is attached to the end connector 15 of the actuator. The first end of the outermost piezo element is attached to the first end of the adjacent, inner piezo element. Correspondingly, the second end of the inner piezo element is coupled to the second end of adjacent, even more inward piezo element, etc. The first end of the innermost piezo element is coupled to the first end of the adjacent, outer piezo element. The second end of the innermost piezo element 12 is attached to the middle end connector 14. The first end of the piezo element 12 is the end on the side of the fuel chamber 3 and the second end is the end further away from the fuel chamber 3. The end connectors 13, 14 are made, for example, of aluminium. The valve needle 9 is attached directly to the middle end connector 14.

The piezoelectric actuator 11 is preloaded, whereby it better withstands tensile stress. Preload is achieved by a preload spring 16, which is located between the end connector 15 and the middle end connector 14 of the actuator. The magnitude of the preload is typically about one tenth of the greatest load of the piezoelectric actuator 11.

Piezo elements 12 are arranged in the actuator 11 such that when a voltage is switched over the piezo elements 12, every other piezo element lengthens and every other one shortens. The change in length occurs in the axial direction of the piezo elements 12.

When injection of fuel begins, the piezoelectric actuator 11 is activated i.e. a voltage is switched to the actuator 11 , whereby the outermost piezo element shortens, the inner piezo element next to it lengthens and the inner piezo element next to this shortens, etc. The innermost piezo element lengthens. The motion of the piezo elements 12 is transferred by the end connectors 13 from the previous piezo element to the next, inner piezo element 12. Thus, the travel distance of the innermost piezo element is the greatest. The piezo elements 12 move telescopically in relation to one another. The second end of the innermost piezo element moves away from the fuel chamber 3. The valve needle 9 attached to the middle end connector 14 moves a distance corresponding to that of the middle end connector 14. Then, the valve needle 9 rises from the seat surface 8 and fuel flows from the fuel chamber 3 through the nozzle openings 7 into the combustion space 4. When injection of fuel into the combustion space 4 is stopped, the voltage supply to the actuator 11 is switched off, whereby the piezo elements 12 return to their original lengths. At the same time, the spring 10 presses the valve needle 9 back against the seat surface 8 and injection of fuel from the fuel chamber 3 into the combustion space 4 ceases. Injection of fuel resumes, when a voltage is once again switched to the actuator 11.

The total travel distance of the valve needle 9 is as great as the absolute value sum of the changes in length of the piezo elements 12. The total travel distance of the valve needle 9 is the lengthening/shortening of one piezo element 12 multiplied by the number of piezo elements 12, in the event that the piezo elements 12 shorten and lengthen by the same amount, when the actuator 11 is activated. The magnitude of the change in length of the piezo elements 12 and thus the magnitude of the movement of the valve needle 9 can be adjusted by altering the magnitude of the voltage switched to the actuator 11. This way, the amount of fuel injection can be adjusted during the injection event. The injection event can, for example, be divided into several parts, which enables more exact control of fuel combustion. The actuator 11 comprises such a number of piezo elements 12 that the valve needle 9 is made to travel the desired distance.

Fig. 3 shows another telescopic type of piezoelectric actuator 11 , which can be used in the injector valve of Fig. 1. The actuator 11 comprises piezo elements 12, which are fitted within each other. The piezo elements 12 are cylindrical. The piezo elements 12 are arranged to move telescopically in relation to each other, when a voltage is switched to the actuator 11. The opposing ends of adjacent piezo elements 12 are coupled to one another by bushings 17. The sec- ond end of the outer piezo element 12 and the first end of the inner piezo element 12 next to it are coupled to each other by a bushing 17. Correspondingly, the second end of the inner piezo element is coupled by a bushing 17 to the first end of the more inward piezo element. The first end of the outermost piezo element 12 is attached to the supporting surface 18 of the body 2. The bushings 17 are made, for example, of aluminium. The valve needle 9 is attached directly to the piezoelectric actuator 11. The other end of the valve needle 9 is attached directly to the second end of the innermost piezo element 12.

The piezoelectric actuator 11 is preloaded, whereby it better withstands tensile stress. Preload is achieved by a preloaded spring 16, which is located between the end 15 of the actuator 11 and the second end of the valve needle 9. The magnitude of the preload is typically about one tenth of the greatest load of the piezo actuator 11.

The piezo elements 12 are arranged in the actuator 11 such that their change in length occurs in the same direction, when a voltage is switched to the actuator 11. In the embodiment according to Fig. 3, each piezo element 12 lengthens, when a voltage is switched to the actuator 11. Using the bushings 17, the motion of the piezo elements 12 is transferred from the previous piezo element to the next, inner piezo element. The travel distance of the innermost piezo element is the greatest. The innermost piezo element moves away from the fuel chamber 3. The total movement of the innermost piezo element and the movement of the valve needle 9 are the same in magnitude as the sum of the length changes of the piezo elements 12. The innermost piezo element 12 can be cylindrical or enclosed, a so-called piezo stack formed from several piezo sheets stacked one on top of the other and onto which the other end of the valve needle 9 is attached.

When injection of fuel begins, the piezoelectric actuator 11 is activated, i.e. a voltage is switched to the actuator 11. Then, the actuator 11 forms an electrical field having such a direction that all the piezo elements 12 lengthen. The piezo elements 12 move telescopically in relation to one another. The innermost piezo element 12 moves away from the fuel chamber 3 and the valve needle 9 attached to it moves a corresponding distance. The valve needle 9 rises from the seat surface 8, whereby fuel is allowed to flow from the fuel chamber 3 through the nozzle openings 7 into the combustion space 4. When injection of fuel from the fuel chamber 3 into the combustion space 4 is stopped, the voltage of the actuator 11 is switched off, whereby the piezo elements 12 shorten to their original lengths and the spring 10 presses the valve needle 9 back against the seat surface 8. Injection of fuel resumes, when a voltage is once again switched to the actuator 11.

The travel distance of the valve needle 9 is equal to the sum of the lengthening or shortening of the piezo elements 12. The total travel distance of the valve needle 9 is the length change of one piezo element 12 multiplied by the number of piezo elements 12, in the event that the piezo elements 12 shorten or lengthen by the same amount, when the actuator 11 is activated. The magni- tude of the change in the length of the piezo elements 12 and thus the magnitude of the movement of the valve needle 9 can be adjusted by altering the magnitude of the voltage of the actuator 11. This way, the amount of fuel injection can be adjusted during the injection event. The injection event can, for example, be divided into several parts, which enables more exact control of fuel combustion. The actuator 11 comprises such a number of piezo elements 12 that the valve needle 9 is made to travel the desired distance. In all the embodiments described above, the motion produced by the actuator 11 is transmitted directly to the valve needle 9 without a hydraulic, mechanical or other motion amplifier, with which the magnitude or strength of the motion produced by the actuator 11 is changed prior to transmission to the valve nee- die 9.

The invention has embodiments that differ from the above described. The piezoelectric actuator 11 can be a so-called Thunder (Thin Unimorph Driver) actuator, which comprises two sheets with different heat expansion coefficients, for example, metal sheets, between which is fitted a layer of piezo material at an elevated temperature. When the temperature drops, the actuator becomes arched. The actuator is attached at its edges to the body of the injector valve. The second end of the valve needle 9 is attached to the midpoint of the arc of the actuator. The actuator lengthens, when a voltage is switched to it, whereby the midpoint of the arc rises upwards, and the valve needle attached to it moves towards the open position.

Instead of piezo elements fitted within each other, the actuator can use piezo elements fitted adjacent to one another, which are attached to one another such that the motion of one piezo element transfers to the next piezo element.

Claims

CLAIMS:

1. A fuel injector valve (1) of a piston engine, which comprises a fuel chamber (3) for the fuel to be injected, a valve needle (9) for guiding the fuel injection from the fuel chamber (3) into the cylinder of the engine (4), and a piezoelectric actuator (11) for guiding the valve needle (9), characterized in that the valve needle (9) is attached directly to the piezoelectric actuator (11).

2. The injector valve (1) according to claim 1 , characterized in that the piezo- electric actuator (11) comprises piezo elements (12), whose length changes, when the actuator is activated.

3. The injector valve (1) according to claim 1 or 2, characterized in that the piezoelectric actuator (11) comprises piezo elements, which are arranged to move telescopically in relation to one another, when the actuator (11) is activated.

4. The injector valve (1) according to claim 1 , 2 or 3, characterized in that the piezoelectric actuator (11) comprises piezo elements (12) fitted within each other.

5. The injector valve (1) according to claim 4, characterized in that each piezo element (12) is coupled from at least one of its ends to an adjacent, inner or outer piezo element (12).

6. The injector valve (1) according to claim 5, characterized in that the adjacent piezo elements (12) are coupled to one another from their ends on the same side.

7. The injector valve (1) according to claim 5, characterized in that the adjacent piezo elements (12) are coupled to one another from their opposing ends.

8. The injector valve (1) according to claim 4, 5 or 6, characterized in that the piezo elements (12) are arranged in the actuator (11) such that in adjacent piezo elements (12) a change in length occurs in the opposite direction, when the actuator (11) is activated.

9. The injector valve (1) according to claim 4, 5 or 7, characterized in that the piezo elements (12) are arranged in the actuator (11) such that in the piezo elements (12) occurs a change in length in the same direction, when the actuator (11) is activated.

10. The injector valve (1) according to any one of preceding claims 2-9, charac- terized in that the valve needle (9) is attached to the innermost piezo element

(12) or the middle end connector (14), which is attached to the end of the innermost piezo element (12).

11. The injector valve (1) according to claim 1 , characterized in that the piezo- electric actuator (11 ) comprises two sheets with different heat expansion coefficients, between which is fitted piezo material.

12. The injector valve (1) according to claim 1 , characterized in that the actuator (11) is arched, and the valve needle (9) is attached to the midpoint of the arc.

13. The injector valve (1) according to any one of the preceding claims, characterized by a spring (10), which is arranged to press the valve needle (9) towards the closed position.