WO2017081210A1

WO2017081210A1 - Piezoelectric actuator

Info

Publication number: WO2017081210A1
Application number: PCT/EP2016/077360
Authority: WO
Inventors: Jean-François Berlemont; Romain Vit
Original assignee: Delphi International Operations Luxembourg S.À R.L.
Priority date: 2015-11-12
Filing date: 2016-11-10
Publication date: 2017-05-18
Also published as: FR3043731A1

Abstract

A piezoelectric actuator (16) of a fuel injector (10) extends along a main axis X and comprises a cage spring (20) extending axially along the axis X, a tubular member (22) extending axially along the axis X, a wire-holder cap (24) extending axially along the axis X, and a piezoelectric element (18) inserted and axially compressed by the cage spring (20). The spring (20) is engaged in the tubular member (22), the spring (20) and the tubular member (22) being attached to the wire-holder cap (24). The piezoelectric actuator (16) further comprises a pre-load adjustment means (26) comprising a regulating member (28) and a push-rod (30), the push-rod (30) being in contact with an upper face (36) of the piezoelectric element (18).

Description

PIEZOELECTRIC ACTUATOR

TECHNICAL AREA

The present invention relates to a piezoelectric fuel injector and more particularly to the preload adjustment of an actuator

piezoelectric.

BACKGROUND OF THE INVENTION

In a direct injection internal combustion engine, a fuel injector is provided for delivering fuel into a combustion chamber. Typically, the fuel injector is mounted in a cylinder head facing the combustion chamber so that its end slightly protrudes into the chamber.

A fuel injector provided with a piezoelectric actuator allows precise control of the injection time and the volume of fuel injected during the fuel injection phase.

A piezoelectric injector known from the prior art is described in EP 1956221 A1.

It is known to those skilled in the art that the piezoelectric actuator is manufactured so that the piezoelectric element is held in mechanical compression by precharging, for example, by means of a cage spring. The piezoelectric element is commonly called by its English name "stack". Each injector is assembled aiming a nominal precharge. Pre-charge of the stack has a direct influence on the performance of the piezoelectric actuator. The precharge value obtained results from a dispersion around the nominal value of the actuator which generates a dispersion of the performances of the piezoelectric injector which is no longer compatible with the evolution of the current requirements.

The object of the present invention is to provide a method of precharging a piezoelectric actuator during assembly in production which will mitigate the problem mentioned above.

SUMMARY OF THE INVENTION

The present invention aims to remedy the disadvantages mentioned above by proposing a simple and economical solution. A piezoelectric actuator of a fuel injector extends along a main axis. The actuator comprises a cage spring extending axially along the main axis, a tubular member extending axially along the main axis, a wire cap extending axially along the main axis , a piezoelectric element inserted and compressed axially by the cage spring. The cage spring is itself engaged in the tubular member, the spring and the tubular member being attached to the wire cap. The piezoelectric actuator further comprises pre-charge adjustment means. The precharge adjusting means comprises an adjusting member and a pusher, the pusher being in contact with an upper face of the piezoelectric element. In addition the adjustment member is provided with an externally threaded cylinder

additionally screwed into an axial bore of the thread cap. In addition the pusher is arranged axially sliding in a portion of the bore of the cap and is compressed between the adjusting member and the element.

piezoelectric. In addition, the adjustment means is provided with means preventing rotation of the pusher member so that the piezoelectric element undergoes only axial compression and not torsion. In addition, the adjustment member is provided with a central bore defining an internally threaded female cylindrical wall and in which the pusher comprises a head arranged to compress the piezoelectric element and from the center of which extends axially a threaded male cylinder screwed into the internal thread of the adjusting member, and wherein the external thread pitch of the adjusting member is greater than the internal thread pitch. The central bore of the adjusting member is open and in which the means prohibiting the rotation of the push member is an engagement means provided in the pusher, said engagement means allowing the complementary engagement of a locking tool of the rotation of the pusher. In another alternative of the embodiment, the central bore of the adjusting member is a blind bore and wherein the pusher and the portion of the bore in which it is arranged are square cross-sections. In another embodiment, the pusher and the section of the bore of the cap in which it is arranged are complementary non-circular transverse sections, this complementary arrangement defining the means preventing the rotation of the pusher. The invention further extends to an injector comprising an actuator such as previously described. In addition, the method of adjusting a piezoelectric actuator comprises the steps of:

providing a piezoelectric actuator as previously described;

supplying the piezoelectric element and measuring an operating characteristic,

- Engage in the axial bore of the cap an adjusting tool,

- Engage the end of the tool in the engagement means of the adjusting means,

- adjust said characteristic to a predetermined value by turning the adjustment member,

- clear the tool.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects and advantages of the invention will appear on reading the detailed description which follows, and with reference to the appended drawings given by way of non-limiting example and in which:

Figure 1 is a longitudinal section of a piezoelectric injector, figure identifying the region of the invention.

FIG. 2 is a longitudinal section of the piezoelectric actuator of the injector of FIG. 1.

FIG. 3 is a longitudinal section of the upper part of the piezoelectric actuator of the injector of FIG. 1, the actuator being a first embodiment of the invention.

FIG. 4 is a view from above of FIG.

Figure 5 is a longitudinal section of the piezoelectric actuator according to a second embodiment of the invention.

FIG. 6 is a view from above of FIG.

FIG. 7 is a longitudinal section of the piezoelectric actuator according to an alternative of the second embodiment of FIG. 5.

FIG. 8 is a view from above of FIG. 7.

Figure 9 is a longitudinal section of the piezoelectric actuator according to a third embodiment of the invention.

FIG. 10 is a view from above of FIG. 9. DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is now described with reference to the figures and for the sake of clarity and conciseness of the description a top-down orientation in the sense of FIG. 1 will be used without any limiting intention as to the extent of the protection, particularly with regard to the different installations of an injector in a vehicle. Words such as "up, down, below, above, vertical, up, down ..." will be used without limiting intent.

A piezoelectric injector 10 shown in FIG. 1 has an elongate shape and extends along a longitudinal axis X. The injector 10 is composed of a control part 12 arranged in the upper part of the injector 10 and a hydraulic part 14 arranged in the lower part of the injector 10. The control part 12 according to Figures 1 and 2 comprises an injector body 13 in which is arranged a piezoelectric actuator 16 cooperating with a control valve. The actuator 16 is provided with electrical connection wires 34, 35 adapted to be powered by an electronic power circuit, controlled and integrated in a motor control unit (ECU) (not shown).

The piezoelectric actuator 16 according to FIG. 2 comprises a piezoelectric element 18, which we will call by its English denomination the

"Stack", inserted into a cage spring 20 and into a tubular member 22. This assembly of concentric shape, the stack 18 in the center and the tubular member 22 at the periphery is surmounted by a thread cap 24 arranged to maintain the Electrical son of 34,35 connections of the stack 18. The piezoelectric actuator 16 further comprises a compression adjustment means 26 of the stack 18, the adjustment means being arranged in the wire cap 24 just above the stack 18 and in contact with it.

The cage spring 20 is briefly described because it is already known from the prior art. The cage spring 20 is a cylindrical and longitudinal. It is perforated on its peripheral wall and extending along the main axis X. It is arranged between the tubular member 22 and the stack 18. The cage spring 20 in its upper part is welded to the thread cap 24, or fixed by any other known method of assembly.

Alternatively, the spring can be a cylindrical tube longitudinally without apertures whose thickness will be chosen to obtain the required elasticity or a cylindrical longitudinal spring of helical shape.

The tubular member 22 is a non-perforated longitudinal cylindrical tube extending along the main axis X so as to ensure the sealing of the stack 18 with respect to the fuel flowing along the actuator 16. upper tubular member 22 is welded to the wire cap 24 or fixed by any other known method of assembly.

The wire cap 24 is arranged to keep the two electrical wires (34, 35) for connecting the stack 18 separate and to guarantee a tightness of the piezoelectric actuator 16. The cap 24 is generally tubular comprising an internal wall defining a bore. longitudinal threaded thread 38 extending along the main axis X. The thread cap 24 should be a rigid material such as steel.

The pre-load adjusting means 26 comprises a setting member 28 additionally screwed into the threaded bore 38 of the cap 24, the adjusting member 28 cooperating with a pusher 30 also arranged in the cap 24 so as to be in contact with the stack 18.

FIGS. 3 and 4 show a first embodiment of the adjustment means 26. The adjustment means 26 is actuated during the manufacture of the injector to adjust a characteristic directly related to the compression of the stack 18. As shown by FIGS. Figures 3 and 4, the electrical son 34,35 are kept separate from each other to pass a setting tool.

According to this first embodiment, the adjusting member 28 is an externally threaded grub screw, with a pitch for example between 0.5 and 1 mm, complementarily screwed into the threaded bore 38 which in this portion has a section generally. circular.

The pusher 30 has on its side a square section and the axial bore 38 of the cap 24 has in this part also a complementary square section allowing axial sliding of the pusher 30, the square sections

complementary cap 24 prevent the rotation induced by screwing the adjustment member 28 is transmitted to the stack 18 which undergoes only a pure axial compression. The square shape may be replaced by any means prohibiting the transmission of rotation, whether it is an asymmetrical shape or the addition of a key.

In manufacture the compression of the stack 18 is adjusted by the axial insertion of an adjusting tool, which is here of the screwdriver type until it engages additionally in an engagement means 42, here a groove, located at the top 46 of the adjustment member 28. Those skilled in the art knows other engagement means 42 such as hexagonal screws, cruciform and the like.

A second embodiment of the adjustment means 26 is now described as illustrated in FIGS. 5 and 6. The adjustment member 28 is here a tubular element, the central bore 52 of which opens out on either side. adjusting member 28 being threaded both internally and externally. The pitch of the external thread is chosen a little larger, for example 0.7 mm, than the internal thread pitch, for example 0.5 mm. The two threads have the same screwing direction, for example the conventional screwing on the right. The thread of the adjusting member 28 is additionally screwed into the thread of the axial bore 38 of the cap 24. The engagement means 42 is here a discontinuous groove comprising two diametrically opposed sections as shown in FIG. embodiment allows other modes of engagement for example by a hexagonal screw.

The pusher 30 here comprises, for example, a square-headed screw 31 from the center of which extends upwards a full threaded cylinder 33 at its periphery. The threaded cylinder 33 whose pitch may be for example 0.5 mm is complementarily screwed inside the adjustment member 28. The square head 31 is always arranged in a complementary bore of the cap 24 so as to prohibit the transmission of rotations .

An advantage of the second embodiment with respect to the first embodiment is a greater adjustment sensitivity with an external thread of the adjustment member 28 slightly larger than the internal screw pitch, for example 0.2 mm, per revolution of the screw to adjust the compression of the stack 18.

In manufacture the adjusting screwdriver (not shown) is axially inserted and complementarily engaged in the two sections of the discontinuous groove 42. Then the screwdriver is rotated until the desired compression of the stack 18 is reached. The rotation of the pusher 30 is prevented by the square sections of the pusher 30 and the cap 24.

An alternative of the second embodiment is shown in FIGS. 7 and 8. The principle of the second embodiment is preserved with an adjusting member 28 provided with two threads and a push-button 30 of the square screw complementarily engaged in the member adjusting 28.

In this alternative, the adjustment member 28 comprises a blind hole 54 and no longer opening at the upper end 46 of the second mode. This alternative makes it possible to have a greater interface between the adjustment tool and the adjustment member 28.

A third embodiment is shown in FIGS. 9 and 10. It is inspired by the tubular adjustment member 28 of the second mode, the central axial threaded bore 52 of which opens out on either side of the adjustment member 28.

Pusher 30 is in this third embodiment a circular head screw 37 from the center of which extends axially upwardly the threaded male cylinder 33. The male cylinder 33 has at its upper end remote from the head 37 another means of commitment 44 for a setting tool. In Figure 10 a groove 44 is shown for the complementary engagement of a screwdriver, which could also be a 6-sided engagement.

During manufacture, the rotation of the pusher 30 is no longer prevented by the circular shape of the head 37 of the thread-holding cap 24. The rotation is prevented by an adjustment tool making it possible both to hold the pusher 30 and turn the adjustment member 28.

This embodiment allows the use of wire cap 24 provided with a cylindrical bore which is already known to those skilled in the art.

The pre-charge setting of stack 18 is now described. The adjustment method consists of a step during the assembly and adjustment of the piezoelectric actuator 16 of the injector 10.

The characterization of the piezoelectric actuator 16 is done by measuring the voltage, the current, the displacement applied on the actuator member 16. The pre-charge adjustment is done by adjusting the adjustment member 28, for example the screwing a screw, which will allow to adjust the elongation of the cage spring 20 between the upper weld of the spring 20 and the lower bearing face of the piezoelectric stack 18. The adjustment of the elongation of the spring 20 is at a given value of given electric charge to obtain a defined elongation.

LIST OF REFERENCES USED

10 injector

12 part order

13 Injector body

14 Hydraulic part

16 Piezoelectric Actuator

18 Stack or piezoelectric element

20 cage spring

22 tubular member

24 Cap Wire Holder

26 Pre-Charge Adjustment Means

28 adjustment member

30 Pusher

31 Square head of the pusher

33 cylinder maie pusher

34 electric wire

35 electric wire

36 upper stack surface

37 Circular pusher head 30

38 Bore the wire cap

40 seal

42 means of engagement of a setting tool = groove of the adjusting means

44 pusher groove 30

46 upper surface of adjustment member 28

52 hole opening of the adjustment member

54 hole not emerging from the adjustment member

56 bore of the lower end of the cap

Longitudinal main axis

Fuel: C

Claims

A piezoelectric actuator (16) of a fuel injector (10), the piezoelectric actuator (16) extending along a main axis (X) and comprising

a cage spring (20) extending axially along the main axis

(X)

a tabular member (22) extending axially along the main axis (X),

a wire-carrying cap (24) extending axially along the main axis (X),

- A piezoelectric element (18) inserted and compressed axially by the cage spring (20), itself engaged in the tubular member (22), the spring (20) and the tubular member (22) being attached to the wire cap (24)

characterized in that the piezoelectric actuator (16) further comprises

pre-load adjusting means (26) comprising a setting member (28) and a pusher (30), the pusher (30) being in contact with an upper face 36 of the piezoelectric element (18),

an engagement means (42) located at an apex (46) of the adjusting member (28) and being arranged to receive a complementarily adjustment tool (48), the compression of the piezoelectric element (18) being then able to be adjusted using the adjustment tool (48).

2. Actuator (16) according to the preceding claim wherein the adjustment member (28) is provided with an externally threaded cylinder.

additionally screwed into an axial bore 38 of the thread cap (24).

A piezoelectric actuator (16) according to claim 2 wherein the pusher (30) is arranged axially slidably in a portion of the bore (56) of the cap (24) and is compressed therebetween between the adjusting member (28) and the piezoelectric element (18).

4. Piezoelectric actuator (16) according to any one of

preceding claim wherein the adjusting means (26) is provided with a means prohibiting the rotation of the pusher member (30) so that the piezoelectric element (18) undergoes only axial compression and not torsion .

The piezoelectric actuator (16) of claim 4 wherein the adjusting member (28) is provided with a central bore (52) defining an internally threaded female cylindrical wall;

and wherein the pusher (30) comprises a head (31) arranged to compress the piezoelectric element (18) and from the center of which extends axially (X) a threaded male cylinder (33) screwed into the internal thread of the member adjusting (28),

and wherein the outer thread pitch of the adjusting member (28) is greater than the internal thread pitch.

The piezoelectric actuator (16) of claim 5 wherein the central bore (52) of the adjusting member (28) is open and

wherein the means prohibiting the rotation of the pusher member (30) is the engagement means (44) provided in the pusher (30), said engaging means (44) allowing the complementary engagement of a locking tool the rotation of the pusher (30).

The piezoelectric actuator (16) of claim 5 wherein the central bore (54) of the adjusting member (28) is a blind bore (54) and wherein the pusher (30) and the bore portion ( 56) in which it is arranged are square cross sections.

8. Piezoelectric actuator (16) according to any one of

Claims 4 to 6 wherein the pusher (30) and the portion of the bore (56) of the cap (24) in which it is arranged are cross-sections

non-circular complementary, this complementary arrangement defining the means prohibiting the rotation of the pusher (30).

A fuel injector (10) comprising a piezoelectric actuator (16) according to any one of the preceding claims.

10. A method of setting a piezoelectric actuator (16), the method comprising the steps of:

- Provide a piezoelectric actuator (16) made according to any one of claims 1 to 8;

- supplying the piezoelectric element (18) and measuring an operating characteristic,

- Engage in the axial bore of the cap (24) a setting tool,

- engaging the end of the tool in the engagement means (42, 44) of the adjusting means (26),

- adjust said characteristic to a predetermined value by turning the adjustment member (28),

- clear the tool.