SERVO ACTUATOR FOR FUEL INJECTOR

Abstract

 An actuator assembly (12) of a fuel injector (10) has a body (14) provided with an internal cavity (22) wherein an inner shoulder face (44) is arranged between a large bore (24) and a thinner conduit (30). A servo actuator member (32) is arranged in the cavity (22) and it has an outer shoulder face (38) provided between a large actuation portion (34) and a thinner head portion (36).
The actuator assembly (12) is further provided with an integral hydraulic lash adjuster (HLA) comprising a first chamber (56) defined between the outer shoulder face (38) and the inner shoulder face (44) and, an annular first clearance (C1) arranged around the actuator member (32) filled with high viscosity fluid (F).

Description

TECHNICAL FIELD

[0001] The present invention relates to an actuator assembly for a fuel injector and more particularly to a servo actuator provided with an integral hydraulic lash adjuster.

BACKGROUND OF THE INVENTION

[0002] Piezo-electric injectors require Hydraulic Lash Adjuster, also called "coupler", arranged between the piezo-electric actuator and the control valve it is actuating. Examples are disclosed for instance in DE 102010029106 and DE 102009000203. This is in order to adapt to slow variations of the lengths of the parts caused by temperature changes and wear. In this position however the added moving mass of the coupler can cause large oscillations of the control valve. Top mounted couplers e.g. EP1519037, WO2013053594, DE102009026532 are also known, but tend to be complex and not as stiff as desirable. The same issue can apply to other actuators such as magnetostrictive.

SUMMARY OF THE INVENTION

[0003] Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing an actuator assembly of a fuel injector, the actuator assembly comprising an elongated body provided with an internal cavity comprising a large portion, here after called large bore, and a thinner portion, here after called thinner conduit. An inner shoulder face is arranged between the large bore and the thinner conduit. The large bore opens in the lower transverse face of the body, said opening being closed by a sealing assembly provided with a central aperture.

[0004] The actuator assembly further comprises a servo actuator member arranged in the cavity, said member having an outer shoulder face provided between a large actuation portion and a thinner head portion. An actuation pin protrudes from the lower face of the large actuation portion and extends through said central aperture, the actuation pin being adapted to cooperate with a valve member. Electrical wires departing from the thinner head portion extend in the thinner conduit, the actuator member expanding or retracting, in use, as being electrically energized.

[0005] Advantageously, the actuator assembly is further provided with an integral hydraulic lash adjuster (HLA) comprising a first chamber defined between the outer shoulder face and the inner shoulder face and, an annular first clearance arranged around the actuator member said first chamber and said clearance being in fluid communication and being filled with high viscosity fluid such as a silicone oil so that, in use, the actuator member is able to displace within the cavity and, when the actuator member expands the pressure in the first chamber raises and, when the actuator member retracts the pressure in the first chamber drops.

[0006] Preferably, the outer shoulder face and the inner shoulder face are tapered pointing toward the head of the actuator body so that said first chamber is sloped.

[0007] A spring member is arranged to permanently solicit the hydraulic lash adjuster HLA toward pressure drop in the first chamber.

[0008] Also, the thinner head portion of the actuator member extends in the thinner conduit with a head clearance fit that is fluid communication with the first chamber.

[0009] A second chamber is defined in the thinner conduit, the head clearance fit being in fluid communication with said second chamber, the fluid at least partially filling said second chamber.

[0010] More particularly, the second chamber is an annular space surrounding the head portion of the actuator member.

[0011] In another HLA embodiment, the actuator member comprises an annular reacting plug secured to the body and arranged between the actuator member and the actual bottom face of the large bore. The reacting plug is provided with an axial aperture defining an initial portion of the thinner conduit and, the inner shoulder face is integral to said reacting plug.

[0012] Said another HLA embodiment may further comprise at least one securing member securing the reacting plug in the body.

[0013] In said another HLA embodiment, a third chamber is defined in the cavity between the reacting plug and the actual bottom face of the large bore, said third chamber being in fluid communication with the first chamber, the thinner conduit opening in said actual bottom face. A fluid absorbing member, or washer, may be arranged in said third chamber, the fluid absorbing member being made for instance of felt or sponge.

[0014] In yet another HLA embodiment of the actuator assembly, the reacting plug is threaded in the large bore and secured in place by a locking screw so that, the volume of the first chamber is adjustable.

[0015] More particularly, both the reacting plug and the locking screw are threaded in the actuator body with thread having same pitch and, furthermore, the reacting plug is also threaded in the locking screw with another pitch.

[0016] Adjusting the position of the reacting plug is made possible thanks to a specific tool able to separately engage with the reacting plug and also with the locking screw, enabling to unlock the reacting plug, adjust its position and re-lock the reacting plug.

[0017] Opposition to the first chamber, the lower face of the actuator member remains at a distance from the sealing assembly defining in-between them a reservoir filled with the high viscosity fluid.

[0018] The actuator assembly may further comprise a fluid filling orifice extending in the wall of the actuator body from an opening in the external lateral face, or in the lower transverse face of the body to an opening in the cavity between the lower transverse face of the actuator member and the sealing assembly, so that fluid may be filled in the bore.

[0019] Whatever the HLA embodiment here above described, the actuator assembly may further comprise a damper assembly arranged between the actuator member and the opening of the large bore.

[0020] The damper assembly comprises a damper body interposed between the actuator member and the control valve, the damper body defining a reservoir in fluid communication with the first chamber and also with a void space arranged between the damper body and the actuator member, said fluid communication enabling a restricted flow between said void space and said reservoir.

[0021] The invention further extends to a fuel injector comprising an actuator assembly a previously described, the actuation pin extending through the central aperture of the sealing member in order to cooperate with a control valve member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is an axial section of a first embodiment of an actuator assembly comprising an integral hydraulic lash adjuster as per the invention.

Figure 2 is an axial section of a second embodiment of an actuator assembly as per the invention.

Figure 3 is an alternative to the second embodiment of figure 2.

Figure 4 is an axial section of a third embodiment of an actuator assembly as per the invention.

Figures 5 and 6 are axial sections of alternatives to the third embodiment of figure 4.

Figure 7 is an axial section of a fourth embodiment of an actuator assembly as per the invention.

Figures 8, 9 and 10 are three plots displacement of the actuator as a function of time.

Figures 11 is a first damper embodiment for a damper arranged in the lower part of the actuator assembly.

Figure 12 is an alternative to the first damper embodiment of figure 11.

Figure 13 is a second damper embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] In reference to the figures is generally described the actuator assembly 12 of a fuel injector 10 comprising an actuator body 14 extending along a longitudinal axis X1, drawn vertical on the figures, the top-down arbitrary orientation of the figures being utilized to ease, simplify and clarify the present description without any intention to limit the invention. The actuator body 14 extends from a head 16, on the top of the figures, where is arranged an electrical connector, not represented,, to a lower transverse face 20 adapted to be in sealing surface contact against the top face of a control valve assembly, not represented. The body 14 is also provided with an internal cylindrical cavity 22 extending inside the body along a cavity axis X2 parallel to the longitudinal axis X1. The cavity 22 comprises a large bore 24 which opens in the lower transverse face 20 and which upwardly extends toward a bottom face 28 wherefrom a thinner conduit 30 upwardly extends toward the connector.

[0024] In the cavity 22 is arranged with clearance fit C a servo actuator member 32, such as a piezo-electric or a magneto restrictive actuator, which has a large cylindrical portion 34, a thinner head portion 36 and an outer shoulder face 38 in-between them.

[0025] The large portion 34 extends in the large bore 24 from a lower face 40, where from axially protrudes a male actuation pin 42, to the outer shoulder face 38 which faces an inner shoulder face 44 integral, or fixed, to the large bore 24. From the outer shoulder face 38 upwardly extends the thinner head portion 36 from which depart electrical wires extending, in the thinner conduit 30, toward the electrical connector.

[0026] The opening 26 of the large bore in the lower transverse face 20 is closed by a resilient sealing assembly 46 comprising a resilient sealing member 48 provided with a central aperture 50 through which extends the actuation pin 42, said sealing assembly 46 sealingly closing the cavity 22, thanks to an O-ring 52 arranged in the central aperture 50 radially compressed between the sealing member 48 and the actuation pin 42.

[0027] The actuator member 32 is arranged in the cavity 22 so that the lower face 40 of the actuator member is inside the cavity 22 at a distance of the sealing member 48 defining between them a reservoir 54.

[0028] The clearance C is to be distinguished in several portions each varying in thickness. A quite thin first clearance C1 of few microns is between the lateral cylindrical faces of the large bore 24 and of the large actuator portion 34. A similar thin first clearance C1 is also between the head portion 36 of the actuator member and the thinner conduit 30. An enlarged second clearance C2 of few tens of microns is between the shoulder faces 38, 44, defining there between a first chamber 56, also identified as a reaction chamber 56. All portions of the clearance C, the first chamber 56 and the reservoir 54 are in fluid communication filled with high viscosity fluid F such as silicone oil having typically a viscosity in the 1,000-500,000 centistokes range.

[0029] The above values of the clearances are given as examples since values depend on the chosen oil and, considering the large range of viscosity, a specific clearance can vary by a factor ten or even hundred.

[0030] In a preferred arrangement represented on the figures, the first chamber 56 is sloped in order to help evacuating toward the top of the injector any bubble of air that would be captured in the fluid F alternatively, the shoulder faces 38, 44, and consequently the first chamber 56 could be made flat or any other shape.

[0031] In operation, the fuel injector 10 is connected to a control unit, not represented, which alternatively energizes or not the actuator member in order to command or to forbid injection events. When the actuator assembly 12 is energized, the actuator member 32 axially expands and the pressure in the first chamber 56 raises, said first chamber 56 acting as a top mounted hydraulic lash adjuster (HLA). As the actuator member 32 expands, the actuation pin 42 pushes a control valve that opens a spill orifice through which pressurized fuel gushes flowing toward an outlet and consequently enabling fuel injection event. To the contrary, when the actuator assembly 12 is not energized, the actuator member 32 retracts to a rest length, the pressure in the first chamber 56 drops and the actuation pin 42 lifts away from the control valve closing the spill orifice and forbidding injection event.

[0032] Also, in time, the dimensions of the actuator assembly 12 slightly vary for instance due to wear or heat dilation of the parts. Thanks to the clearance C filled with fluid F, the actuator member 32 is able to accommodate with said dimensions variations.

[0033] Following the general description, a first HLA embodiment of the actuator assembly 12 is now further detailed in reference to figure 1.

[0034] In this first HLA embodiment the thinner head portion 36 of the actuator member extends in the conduit 30 up to a distal upper extremity 58 above which the conduit 30 is provided with a conduit shoulder face 60 further restricting said conduit in its upper most part. An actuator spring 62 is compressed between the conduit shoulder face 60 and the upper extremity 58 of the head portion so that, it permanently downwardly solicits the actuator member 32 toward the sealing assembly 46. The head portion 36, which fits with first thin clearance C1 in the thinner conduit 30, is further provided with a recessed central section 64 defining in the thinner conduit 30 an annular chamber 66, or second chamber 66, that is in fluid communication with said first clearance C1 and first chamber 56.

[0035] The fluid fill volume comprises the reservoir 54, the thin clearance C1 in the large bore, the first chamber 56, the thin clearance C1 in the conduit and a part of said second chamber 66, half for instance. When the actuator assembly 12 varies in dimension the level of fluid in the second chamber 66 ensures fluid F presence in all parts of said fill volume.

[0036] A second HLA embodiment of the actuator assembly 12 is now detailed in reference to figure 2.

[0037] In this second HLA embodiment, an annular reacting plug 68 in inserted with interference fit in the cavity 22 up to the vicinity of the bottom face 28 of the large bore and it is secured to the actuator body 14 between said bottom face 28 and the actuator member 32. The inner shoulder face 44 is indeed integral to said annular plug 68, the reaction first chamber 56 being formed between the outer shoulder face 38 of the actuator member and the inner shoulder face 44 of the plug 68. The reacting plug 68 is also provided with an axial aperture 70 aligned with the thinner conduit 30, the thinner head portion 36 of the actuator member extending with thin clearance C1 through said aperture 70 before extending in the conduit 36. As the plug 68 is not in abutment against the actual bottom face 28 of the large bore, a third chamber 72 is arranged between the reacting plug 68 and said actual bottom face 28, said third chamber 72 being, similarly to the second chamber 66 of the first HLA embodiment, an expansion volume partially filled with fluid F ensuring that thin clearance C1 and first chamber 56 are permanently filled with fluid. An advantage of said second HLA embodiment is that the third chamber 72 is larger in section making this second HLA embodiment less sensitive to the angle of operation of the injector 10.

[0038] Furthermore, as represented on figure 2 a fluid absorbing washer 74 made of a material such as felt or sponge may be arranged in said third chamber 68. By capillary action, the absorbing material attracts the fluid F ensuring that there is permanently fluid F present to the third chamber 72 adjacent to the thin clearance C1 and the first chamber 56 irrespective of the orientation of the injector 10.

[0039] In an alternative HLA embodiment presented in figure 3, the plug 68 can be secured thanks to a specific securing member 76, such as a screw or a plurality of screws, radially arranged in the actuator body 14. In the example presented the screw is designed with a drive region which shears off in order to fit them in a thin walled housing. Also, sealant or adhesive can be applied on the threads or on the outer circular face of the reacting plug 68 in order to ensure sealing of the injector 10.

[0040] In reference to figure 4 is now described a third HLA embodiment which is also an alternative to either of the first or the second embodiment.

[0041] Normally a piezo-electric actuator member 32 has a metal encapsulation 78 inside of which a piezo stack 80 is axially compressed in a very stiff cage spring 82 having a tubular body provided with a plurality of transverse apertures 84 providing to the body the required axial stiffness. The metal encapsulation 78 protects the piezo stack 80 from environmental factors such a as humidity which could lead to dielectric breakdown and, an air gap exists between the cage spring 82 and the internal face of the metal encapsulation 78. Such actuator member 32 is represented on figures 1, 2 and 3.

[0042] In this third HLA embodiment the actuator member 32 is not provided with metal encapsulation; silicone oils having a high dielectric strength of around 10-15kV/mm and, in the high viscosity variants the oils being compatible with silicone coatings that are often used to passivate, meaning electrically insulate, the piezo stack 80, therefore, in this third embodiment the metal actuator encapsulation 78 has been removed and the actuator member 32 is running directly in silicone oil. The oil replaces the air gap and it flows through the transverse apertures 84 to be in direct contact with the piezo stack 80. Although the cost related to the encapsulation 78 may be saved, the dissipation of heat from the piezo stack 80 is improved resulting in the stack 80 running at lower temperatures, which is known to be beneficial for the life of the piezo stack 80.

[0043] It is important to isolate the silicone oil from exposure to fuel. One reason is that fuel has low viscosity and could affect the hydraulic lash adjuster performance. The sealing performance of the sealing assembly 46 of figures 1 to 4 is assured by the O-ring 52 compressed between the wall of the central aperture 50 of the sealing member 48 and the actuation pin 42. Several alternative embodiments of the sealing assembly as well as methods of assembly and operations are detailed in application GB1511355 filed 29 June 2015.

[0044] As part of the assembly method, the actuator member 32 is arranged in the cavity 22, the sealing member 48 is fixed in the opening 26 and, the fluid F is flown in the cavity, filling the fluid fill volume, before arranging the O-ring 52 in the sealing member 48.

[0045] Also, fuel is able to carry water which is known to shorten the life of piezo-electric stacks and, the facts that hydrocarbons do not mix with silicone oil and that fuel is less dense than silicone oil give the ability for fuel to rise through the oil and be purged into the expansion volume. A very limited quantity of fuel may be acceptable but, in the third HLA embodiment where the actuator member 32 runs directly in the oil, if the O-ring 52 is found to be too permeable to fuel, then an alternative way to provide a flexible seal is to use. Instead of the sealing assembly 46 previously described, a metal diaphragm 86, figure 5, or bellows 88, figure 6, welded to the actuator body 14 and to the actuation pin 42 would be used. As welding would be done prior to filling the silicone oil, this in order to avoid weld contamination, a separate filling orifice 90 would be added and would typically be plugged with a metal ball 92 or a plug after filling the oil. Such filling orifice 90 is represented on figures 5 and 6 and, it extends in the wall of the actuator body 14 from an opening in the lower transverse face 20 of the body, or alternatively in the outer peripheral face, to another opening in the cavity 22.

[0046] A fourth HLA embodiment of the actuator assembly 12 is now detailed in reference to figure 7.

[0047] As the first chamber 56 represents compliance in series with the actuator member 32, by adjusting the volume of the first chamber 56, it is possible to change the charge required for the actuator member 32 to get to a given force. If this can be done on a running fuel injector then it is possible to adjust either the injector opening delay, or fuel delivery for a given actuator charge level and thus minimise injector to injector variability. Figure 7 shows a scheme which can provide such adjustability. The force reacting plug 94 which in previous HLA embodiments is secured to the actuator body 14 is, in the fourth HLA embodiment a threaded fit both with the support actuator body 14 and a locking screw 96. The conduit shoulder face 60 that is in the first HLA embodiment arranged in the thinner conduit 30 is, in the fourth HLA embodiment, arranged in the axial aperture 70 of the threaded reacting plug 94 and, the actuator spring 62 is compressed between said conduit shoulder face 60 and the actuator member 32. The spring 62 is used both to bias the actuator member 32 downwards and to bias the threaded force reacting plug 94 upwards. This removes any play in the threads while they are being adjusted. The internal and external threads of the locking screw 96 are made with different pitches and/or different handedness. The external thread is machined along with that on the force reaction plug 94 whilst they are tightened against each other, to effectively give a single thread during assembly and adjustment. To lock the threads after adjustment, the locking screw 96 is rotated so as to move it upwards, pulling the force reaction plug 94 upwards via the internal thread. A special tool 100 is used to engage drive features e.g. hexagonal sockets or splines on the locking screw 96 and force reaction plug 94. This tool 100 is inserted into the top of the actuator body 14 whilst the actuator wires are passed through a bore in the tool 100 and connected to a drive circuit.

[0048] Whilst the designs of hydraulic lash adjuster described in all the HLA embodiments have a very low moving mass, they do not provide much damping of the actuator motion. Figure 8, 9 and 10 are plots of displacement of the actuator assembly 32 as a function of time.

[0049] Figure 8 is shows a typical response to a constant current charging pulse. Thanks to the low moving mass, an overshoot 102 is a small proportion of the stroke. Because of the low self-damping of a typical piezo-electric actuator though, the following oscillation takes many cycles to decay.

[0050] Figure 9 shows that with a small amount of additional damping, the magnitude of the overshoot 102 can be reduced and the time for the oscillation to decay to significantly decrease.

[0051] As shown in figure 10, with an optimum damping level it is possible to completely eliminate the overshoot, whilst still maintaining a fast response to the charge current pulse. This is particularly advantageous when it is desired to use the piezo-electric actuator as a sensor to detect forces in the injector as a means of closed loop control. The actuator can move fast for actuation, but any force changes shortly after can also be seen clearly as they are not hidden in oscillations.

[0052] A first damper embodiment is now described in reference to figure 11 and it shows a method to add damping to the design of the previous HLA embodiments.

[0053] A damper assembly 104 is arranged in the opening of the large bore 24, said assembly 104 comprising a generally cylindrical damper body 106 having a base portion 108 inserted with interference fit in the opening 26 of the large bore and also with, a top portion 110 smaller in section than the base portion 108, said top portion 110 being inserted with clearance fit C3 in the metal encapsulating tube 78. Between said base portion 108 and said top portion 110, the damper body 106 is provided on its external face with a deep annular recess 112 forming a fluid reservoir R arranged at the bottom of the actuator member. The top portion 110 of the damper body is provided with one, or more, damper orifice 114 joining the top face of the damper body 106 to said reservoir R, the damper orifices 114 being provided with throttle restricting the orifices section in order to amortize fluid pressure pulses.

[0054] The metal diaphragm 86 which is conventionally used to seal the actuator is secured between the inner face of the metal encapsulation tube 78 and the piezo stack 80, the tube 78 extending beyond said diaphragm over the top portion 110 of the damper body 106.

[0055] The damper body 106 is further provided with an axial through bore 116 opening in a large axial recess 118 formed in the base portion and in the centre of the annular recess 112. The actuation pin 42 extends with minor clearance fit C4 through the bore 116 and it protrudes in the large recess 118 where the O-ring 52 radially compressed between the circular wall of the recess 118 and the actuation pin 42 ensures fluid sealing of the cavity 22.

[0056] In addition to the first chamber 56 and the thin clearance C1, the fluid fill volume comprises the reservoir R, the damper orifices 114, the void between the diaphragm 86 and the top portion 110 of the damper body, the annular clearance C3 around the top portion of the body and, the clearance C4 around the actuation pin 42.

[0057] An advantage of having a large reservoir R of viscous fluid F at the bottom of the actuator member 32 is that this can be used to provide a damping of the actuator motion, with only additional features on existing components. The metal diaphragm 86 may be made to act as a piston forcing fluid through the damper orifices 114. The high viscosity of the fluid F means that a relatively large tolerance annular clearance C3 with the actuator encapsulation tube 78 is able to seal well enough for the majority of the displaced fluid to go through the damper orifices 114. Similarly the fourth clearance C4 around the actuation pin is able to prevent fluid pressure pulses in the damper from disturbing the O-ring 52.

[0058] An alternative to the first damper embodiment is presented on figure 12 where the actuator member is running directly in the silicone oil F, the encapsulation tube and diaphragm being therefore eliminated. As shown on figure 12, the top face of the damper body is provided with a top recess 120 in which is arranged, with fifth clearance fit C5, the lower part of the actuator member 32.

[0059] A second damper embodiment is presented on figure 13 where the damper assembly 104 comprises a body 106 limited to the base portion 108 of the damper body previously described and also, an flange 122 radially extending and secured to the actuator member 32 at a small axial distance of the top face of the body. The flange 122 is slightly smaller than the large bore 24, a sixth annular clearance C6 being maintained between said flange 122 and said bore 24. If manufacturing tolerances are well enough controlled, this sixth clearance C6 may be used to provide the necessary damping restriction for the fluid to flow through but, higher accuracy of damping is usually obtainable by making this clearance close and adding calibrated orifices, flats or slots 124 going through the flange 122.

LIST OF REFERENCES

[0060] 

X1

longitudinal axis

X2

cavity axis

C

clearance

C1

first portion of the clearance

C2

second portion of the clearance

C3

third damper large clearance

C4

fourth clearance - damper

C5

fifth clearance

C6

sixth annular clearance

F

fluid - silicone oil

HLA

hydraulic lash adjuster

R

reservoir

10

injector

12

actuator assembly

14

actuator body

16

head of the body

20

lower transverse face of the body

22

cavity

24

large bore

26

opening of the large bore in the lower transverse face

28

bottom face of the large bore

30

thinner conduit

32

actuator member

34

large actuator portion

36

thinner head portion

38

outer shoulder face of the actuator member

40

lower face of the actuator member

42

actuation pin

44

inner shoulder face of the bore

46

sealing assembly

48

sealing member

50

central aperture

52

O-ring

54

reservoir

56

first chamber

58

upper extremity of the head portion of the actuator member

60

conduit shoulder face

62

actuator spring

64

recessed central section

66

annular chamber - second chamber

68

annular reacting plug

70

axial aperture

72

third chamber

74

absorbing washer

76

securing member

78

metal encapsulation

80

piezo stack

82

cage spring

84

transverse apertures

86

metal diaphragm

88

bellows

90

filling hole

92

plug

94

threaded reacting plug - fourth embodiment

96

locking screw

100

tool

102

overshoot

104

damper assembly

106

damper body

108

base portion of the damper body

110

top portion of the damper body

112

deep annular recess

114

damper orifice

116

axial through bore

118

large axial recess

120

top recess in the damper body

122

flange

124

orifice, flats or slots through the flange

Claims

1. Actuator assembly (12) of a fuel injector (10), the actuator assembly (12) comprising:

an elongated body (14) provided with an internal cavity (22) wherein an inner shoulder face (44) is arranged between a large bore (24) and a thinner conduit (30), the large bore (24) opening in the lower transverse face (20) of the body, said opening (26) being closed by a sealing assembly (46) provided with a central aperture (50) and,

a servo actuator member (32) arranged in the cavity (22), said member (32) having an outer shoulder face (38) provided between a large actuation portion (34) and a thinner head portion (36), an actuation pin (42) protruding from the lower face of the large actuation portion and extending through said central aperture (50), the actuation pin (42) being adapted to cooperate with a valve member and, electrical wires departing from the thinner head portion (36) extending in the thinner conduit (30), the actuator member (32) expanding or retracting, in use, as being electrically energized,

characterized in that

the actuator assembly (12) is further provided with an integral hydraulic lash adjuster (HLA) comprising a first chamber (56) defined between the outer shoulder face (38) and the inner shoulder face (44) and, an annular first clearance (C1) arranged around the actuator member (32), said first chamber (56) and said clearance (C1) being in fluid communication and being filled with high viscosity fluid (F) such as a silicone oil so that, in use, when the actuator member (32) expands the pressure in the first chamber (56) raises and, when the actuator member (32) retracts the pressure in the first chamber (56) drops.

2. Actuator assembly (12) as claimed in the preceding claim wherein the outer shoulder face (38) and the inner shoulder face (44) are tapered pointing toward the head of the actuator body (14) so that said first chamber (56) is sloped.

3. Actuator assembly (12) as claimed in any of the preceding claims further comprising a spring member (62) permanently soliciting the hydraulic lash adjuster (HLA) toward pressure drop in the first chamber (56).

4. Actuator assembly (12) as claimed in any of the preceding claims wherein the thinner head portion (36) of the actuator member (12) extends in the thinner conduit (30) with a head clearance fit (C1) that is fluid communication with the first chamber (56).

5. Actuator assembly (12) as claimed in claim 4 wherein a second chamber (66) is defined in the thinner conduit (30), the head clearance fit being in fluid communication with said second chamber (66), the fluid at least partially filling said second chamber (66).

6. Actuator assembly (12) as claimed in claim 5 wherein the second chamber (66) is an annular space surrounding the head portion of the actuator member.

7. Actuator assembly (12) as claimed in any of the claims 1 to 4 further comprising an annular reacting plug (68) secured to the body (14) and arranged between the actuator member (32) and the actual bottom face (28) of the large bore, the reacting plug (68) being provided with an axial aperture (70) defining an initial portion of the thinner conduit (30), the inner shoulder face (44) being integral to said reacting plug (68).

8. Actuator assembly (12) as claimed in claim 7 further comprising at least one securing member (76) securing the reacting plug (68) in the body (14).

9. Actuator assembly (12) as claimed in any of the claims 7 or 8 wherein a third chamber (72) is defined in the cavity (22) between the reacting plug (68) and the actual bottom face (28) of the large bore, said third chamber (72) being in fluid communication with the first chamber (56), the thinner conduit opening in said actual bottom face (28).

10. Actuator assembly (12) as claimed in claim 9 further comprising a fluid absorbing member (74) arranged in the third chamber (72), the fluid absorbing member (74) being made for instance of felt or sponge.

11. Actuating assembly (12) as claimed in claim 7 wherein the reacting plug (94) is threaded in the large bore (24) and secured in place by a locking screw (96) so that, the volume of the first chamber (56) is adjustable.

12. Actuator assembly (12) as claimed in any of the preceding claims wherein the lower face (20) of the actuator member remains at a distance from the sealing assembly (46) defining in-between them a reservoir (54) filled with the high viscosity fluid (F).

13. Actuator assembly (12) as claimed in any of the preceding claims further comprising a fluid filling orifice (90) extending in the wall of the body from an opening in the external lateral face, or in the lower transverse face of the body to an opening in the cavity (22) between the lower transverse face of the actuator member and the sealing assembly, so that fluid (F) may be filled in the bore.

14. Actuator assembly (12) as claimed in any of the preceding claims further comprising a damper assembly (104) arranged between the actuator member (32) and the opening (26) of the large bore.

15. Fuel injector (10) comprising an actuator assembly (12) as claimed in any of the preceding claims, the actuation pin (42) extending through the central aperture (50) of the sealing member in order to cooperate with a control valve member.

Drawing