SEALING ARRANGEMENT

Abstract

 A sealing arrangement (20) comprising an elastomeric O-ring (26) radially compressed in an annular passage (28) between a shaft (24) and a bore (22) extending along a longitudinal axis (X), the shaft (24), in use, reciprocally axially translating relative to the bore (22) and, the sealing arrangement (20) is adapted to force the O-ring (26) to roll on the shaft (24) and on the bore (22) when the shaft (24) translates relative to the bore (22).

Description

TECHNICAL FIELD

[0001] The present invention relates to a sealing arrangement particularly used in a servo injector.

BACKGROUND OF THE INVENTION

[0002] Conventionally a metal diaphragm or bellows is used when a force and/or motion needs to be transmitted between different fluids without the fluids mixing and without causing frictional forces. Examples include Pressure transducers as disclosed in EP2759607, valves as in EP2807411 and piezo-electric actuators described in EP1431569. A problem with such devices is that they are relatively expensive and it can require a lot of space to achieve sufficient movement without being over-stressed or generating excessive forces. It is well known to use an O-ring as a fluid seal, but these are known to have high friction and fluid seepage when they are sliding.

SUMMARY OF THE INVENTION

[0003] Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a sealing arrangement comprising an elastomeric O-ring radially compressed in an annular passage between a shaft and a bore extending along a longitudinal axis, the shaft, in use, reciprocally axially translating relative to the bore.

[0004] Advantageously, the sealing arrangement is adapted to force the O-ring to roll on the shaft and on the bore when the shaft translates relative to the bore so that sliding of the O-ring is avoided and sealing is ensured.

[0005] In an embodiment, the shaft is provided with an annular groove in which is placed the O-ring, said O-ring rolling, in use, between the two edges of the groove so that when the shaft ends a longitudinal translation the annular passage restricts and the O-ring gets further compressed.

[0006] In another embodiment the bore is provided with a narrowing portion arranged at a first end of the portion of the bore so that under the influence of fuel pressure peaks the O-ring further deforms and further compresses in said narrowing portion.

[0007] In an alternative embodiment, the bore may be provided with a second narrowing portion arranged at a second end of the portion of the bore.

[0008] The invention also extend to an actuator assembly of a fuel injector, the actuator assembly extending along the longitudinal axis, an end of said actuator assembly being provided with a shaft member extending through a bore, the annular passage between the shaft and the bore being sealed by an O-ring, the shaft, the bore and the O-ring defining a sealing arrangement as described above.

[0009] The actuator assembly may further comprise a cylindrical sleeve closed at an extremity by a closing member having a wall defining the bore through which extends the shaft; said wall further defining a conical peripheral wall adapted to deform to be press-fitted inside the extremity of the sleeve.

[0010] The invention further extends to a method to assemble such actuator assembly wherein the method comprises the steps of:

a) providing an O-ring, a resilient closing member and a servo actuator arranged in a cylindrical sleeve ; the closing member defining a bore adapted to receive the O-ring and, the servo actuator having a shaft protruding out of the sleeve,

b) providing a tool, having a tubular member adapted to engage in the annular passage, said tubular member defining an upper annular face ;

c) positioning said upper annular face in contact with the O-ring ;

d) pushing the O-ring inside the annular passage.

[0011] Also, the shaft may be provided with an annular groove as described above and, in such a case, the method further comprises, before step d) the following step:

e) positioning the O-ring around the shaft in place in the groove and; during step d) the tool ensures that the O-ring remains inside the groove.

[0012] Also, the bore may be provided with two narrowing portions as described above and, in such a case, the tool provided at step b) further comprises a base plate adapted to receive the closing member, the tubular member projecting from the base plate and forming an integral centrally tubular projection and,
during step c) the closing member is arranged on the base plate of the tool and is presented in face of the cylindrical sleeve and,
during step d) the closing member is press-fitted inside the sleeve, the O-ring being pushed in place in the annular passage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is an axial section detailing an extremity of a servo actuator provided with a first embodiment of sealing arrangement as per the invention.

Figure 2 details a manufacturing assembly of the arrangement of figure 1.

Figure 3 is a second embodiment of the sealing arrangement.

Figures 4 to 7 represent a third embodiment of the sealing arrangement.

Figure 8 details a manufacturing assembly of the arrangement of figures 4 to 7.

Figure 9 is a fourth embodiment of the sealing arrangement.

Figure 10 is a fifth embodiment of the sealing arrangement.

Figure 11 details a manufacturing assembly of the fifth embodiment of the sealing arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] In reference to the figures are described several embodiments of a fuel servo injector 10, piezoelectric for instance, wherein a servo actuator assembly 12 cooperates with a control valve, not represented, indirectly enabling or forbidding injection of fuel. The actuator assembly 12 extends along longitudinal axis X and, it comprises an actuator member 14 enclosed in a cylindrical sleeve 16 closed at an extremity by a resilient closing member 18 and a sealing arrangement 20 defined by an axial bore 22 provided in the wall of the closing member 18, a shaft 24 of the actuator member 14 extending through the bore 22 and, an elastomeric O-ring 26 sealing the annular passage 28 between the shaft 24 and the bore 22 by being radially compressed both outwardly by the shaft 24 and inwardly by the bore 22.

[0015] The closing member 18 is an axisymmetric solid of revolution made by stamping a metal sheet, or other metal forming process, the constant wall thickness of the member 18 defining an outer peripheral wall 30 press-fitted and fixed, potentially by laser welding or other fixing means, inside the sleeve 16 and, an inner cylindrical tubular extension 32 which inside face defines the bore 22.

[0016] In a free state the O-ring is a torus having a circular cross-section, as shown on figure 2, an inner diameter ID and an outer diameter OD. Once in place in the sealing arrangement 20, as shown on figure 1, the O-ring is compressed and its cross section deforms to adjust to the shaft 24 that has a shaft diameter SD superior to the inner diameter ID of the O-ring and, to the bore 22 that has a bore diameter BD smaller that the outer diameter OD of the O-ring.

[0017] In operation, the actuator member 14 axially expands and retracts so the shaft 24 reciprocally translates by few hundredths of millimeters along the longitudinal axis X within the bore 22 and, since fuel is present outside the actuator assembly 12 and, must not get in contact with the actuator member 14 inside the sleeve, it is crucial that the O-ring 26 perfectly seals the annular passage 28.

[0018] Furthermore, when the actuator 14 expands and the shaft 24 downwardly translates, it pushes the control valve to open a discharge port through which pressurized fuel gushes generating pressure peaks in the return fuel flow flowing toward a low pressure reservoir. Under the influence of these pressure peaks, the O-ring, further deforms and compresses permanently ensuring this sealing characteristic.

[0019] When the shaft 24 translates, it forces the O-ring 26 to roll both on the shaft 24 and on the bore 22 eliminating sliding with high friction and, when pressure peaks occurs, the O-ring deforms still sealing the annular passage 28.

[0020] In a preferred embodiment, the O-ring has dimensions chosen so it is compressed around the shaft 24 and inside the bore 22. As an illustrative and none limiting example, in the case of a 3 mm shaft diameter SD extending in a 5 mm bore diameter BD, an O-ring having an inner diameter ID of 2.9 mm and an outer diameter OD of 5.25 mm can be chosen since, once in place the O-ring is radially compressed both outwardly by the shaft and inwardly by the bore.

[0021] A first embodiment of the sealing arrangement 20 is depicted on figure 1 where the shaft 24 and the bore 22 are parallel and concentric cylinders of revolution. The O-ring 26 has deformed so its cross-section is now elongated in an oblong shape and it contacts the shaft and the bore along large contact areas. In use, when the shaft 24 downwardly translates in the bore 22, the O-ring 26 rotates so that the oblong section of the O-ring represented on the right of the figure rotates in the counter-clockwise direction and the oblong section represented on the left of the figure rotates in the clockwise direction.

[0022] In the opposite direction, when the shaft 24 upwardly translates in the bore 22, the O-ring 26 rotates so the oblong section of the O-ring represented on the right of the figure rotates in the clockwise direction and, the oblong section represented on the left of the figure rotates in the counter-clockwise direction.

[0023] Considering that in the application of a fuel injector, the displacements of the shaft are inferior to the large areas of contacts and also to the manufacturing tolerances of elastomeric O-rings, the rotations of the O-ring are indeed minimal and much smaller than the deformations due to the pressure peaks.

[0024] Since the shaft 24 and the bore 22 have constant diameters, a key characteristic of this first embodiment of the sealing arrangement 20 is that the O-ring compression remains identical throughout the translations of the shaft. The only variations of compression are due to pressure peaks.

[0025] The rotating motion of the O-ring 26 ensures permanent sealing of the annular passage 28, it eliminates friction of the shaft inside the O-ring and it minimizes wear of the O-ring thus enhancing its longevity.

[0026] In this entire description the up-down and left-right directions of the figures are utilized to ease and clarify the understanding without any intent to limit the scope of the application in particular in regard of the actual installation orientation of the fuel injector on an engine.

[0027] In reference to figure 2 is represented a presentation step 110 of the assembling method 100 of the first embodiment of the sealing arrangement 20. In said presentation step 110 the annular passage 28 is open; the O-ring 26 is in a free-state with non-deformed circular cross-section, simply placed on a first tool 112. The O-ring 26 is presented before the annular passage 28 at the extremity of the shaft 24. The first tool 112 has a tubular shape able to fully engage in the annular passage 28 and, the O-ring 26 lies on the upper annular face 114 of the first tool 112. In a subsequent not represented installing step, the first tool 112 moves upward and pushes the O-ring 26 inside the annular passage 28, forcing it to deform and to engage between the shaft 24 and the bore 22.

[0028] In reference to figure 3 is described a second embodiment of the sealing arrangement 20, said second embodiment operating in a similar O-ring rolling way as the first embodiment. The second embodiment of the sealing arrangement 20 only differs from the first embodiment by the shaft 24 that is provided with an annular groove 34 wherein is positioned the O-ring 26. The closing member 18 remains identical to the first embodiment of figures 1 and 2, the tubular extension 32 having a constant and non-restricted bore diameter BD.

[0029] The annular groove 34 has an arcuate profile intersecting the cylindrical face of the shaft in a lower edge 38 and in an upper edge 40, the longitudinal chord C of the groove 34, being measured along the axis X between the edges 38, 40. In this second embodiment, the nominal dimension of the annular passage 28 is measured between the cylindrical face of the bore 22 and the bottom or center of the groove 34.

[0030] When the shaft 24 translates around a central position represented on figure 3 the O-ring rolls between the bottom of the groove and the cylindrical face of the bore. In this central position, the O-ring occupies the annular passage 28 in its nominal dimension and it is compressed to a nominal value but, when the shaft 24 translates to an extreme downward position the O-ring 26 rotates to the vicinity of the upper edge 40 where the section of the annular passage 28 restricts, further compressing the O-ring beyond said nominal compression value. This further compression ensures the required sealing characteristic when the shaft is in extreme downward position.

[0031] In the opposite direction, when the shaft 24 translates to an upper extreme position, the O-ring 26 rotates in the groove to the vicinity of the lower edge 38 and in the cylindrical bore 22, the section of the annular passage 28 restricting further compressing the O-ring and ensuring the required sealing characteristic.

[0032] Fuel pressure peaks may further compress and further deform the O-ring toward an edge or even partially over an edge.

[0033] A third embodiment is now described in total reference to figures 4 to 7, the third embodiment of the sealing arrangement 20 differing from the second embodiment only by the profile of the tubular extension 32 that is provided, as shown on these figures, with an upper narrowing portion 36 arranged at the inner extremity of the tubular extension 32, said inner extremity 32 being the extremity of the tubular extension that is inside the sleeve 16 closer to the actuator member 14. The narrowing portion 36 may have a cylindrical shape or a conical shape.

[0034] This distinctive feature mainly influences the sealing arrangement 20 when fuel pressure peaks occur, as represented on figure 5. Said pressure peaks upwardly push the O-ring which is further compressed between the shaft, which diameter increases, and the bore, which diameter decreases in the narrowing portion 36.

[0035] When the shaft translates in the downward direction, figure 6, the O-ring compression increases from the nominal value to a higher value and, when the shaft translates in the upward direction, figure 7, the O-ring compression increases from the nominal value to another higher value.

[0036] Also, as previously mentioned the actual rotation of the O-ring remains minimal throughout the shaft small displacements. The main deformations of the O-ring are due to the pressure peaks and, comparing figures 4 and 5 it can be observed that when the shaft is in nominal position, in absence of fuel pressure peaks, figure 4, the O-ring lies at the bottom of the groove and, when a fuel pressure peaks occurs, figure 5, the O-ring is pushed upward toward the upper edge 40 of the shaft and the within the narrowing portion 36 of the bore, where it gets further deformed and further compressed, said further compression ensuring sealing of the annular passage 28 throughout the operational phases of the actuator.

[0037] Also, for clarity of the illustrations, the displacements of the shaft of the actuator member of a fuel injector are largely magnified in the figures 6 and 7, considering that said displacements are actually of few hundredths of a millimeter but, an exact representation would not allow distinguishing the positions.

[0038] Also, the environment of a fuel injector is chosen as an example, the sealing arrangements as described being adapted to any other applications where a shaft translates in a bore and where sealing is required.

[0039] Alternatively to the arcuate profile represented on the figures, the groove can accommodate other profiles such as a trapezoidal profile enabling conical portions on both sides of a flat bottom, said conical portions restricting the section of the annular passage 28.

[0040] In a fuel injector environment where the displacements are very small, as mentioned above, a groove having a triangular profile may also fit the sealing purpose and the variation of compression of the O-ring.

[0041] As part of the method 100 to assemble the sealing arrangement 20, figure 8 illustrates the presentation step 110 that is common for the second and for the third embodiments.

[0042] At first, inside the sleeve the actuator member 14 is in a downward position and the shaft largely protrudes below the closing member 18. In said position the O-ring is engaged around the shaft 24 where it lies radially compressed in the bottom of the groove. Then the actuator member 14 is pulled up inside the sleeve, the first tool 112 maintaining the O-ring in place in the bottom of the groove. During this upward movement, the O-ring engages in the annular passage 28 and gets compressed around the shaft and inside the bore.

[0043] In reference to figure 9 is described a fourth alternative of the sealing arrangement 20, said alternative operating with a similar rolling principle of the O-ring. The shaft 24 has a large circular section portion 44 and a narrow circular section portion 46, the large portion 44 being inside the sleeve 16 close to the actuator member 14 and, the narrow portion 46 largely extending in the bore and being close to the extremity of the shaft. Between these two cylindrical surfaces is a fillet 48 tangent to the narrow cylindrical surface.

[0044] The closing member 18 is identical to the one presented in the third embodiment, the tubular extension 32 being provided with a narrowing portion 36 arranged at the inner extremity of the tubular extension 32.

[0045] In use, when the shaft axially translates, the O-ring rolls on the narrow circular portion 46 of the shaft and also in the cylindrical bore 22. When the shaft reaches its extreme upward position, the O-ring slightly gets in the narrowing portion 36 of the bore where it is further compressed between said bore and the narrow portion 46 of the shaft and, when the shaft reaches its extreme downward position, after rolling on the narrow portion 46 of the shaft, the O-ring slightly gets on the fillet 48 and it is further compressed between said bore and the fillet 48. Similarly to the other embodiments, the most important deformations of the O-ring are due to the influence of pressure peaks pushing on the O-ring deforming and getting further compressed between the fillet 48 and the narrowing portion 36 of the bore.

[0046] Since the shaft 24 is provided with the fillet 48, and the bore 22 with the narrowing portion 36, positioning of these features relative to each other is actually quite important to ensure that the O-ring is well supported and doesn't slide on one of the surfaces when pressure is applied.

[0047] From a process stand point, the assembly of the O-ring is similar to the method used in the first embodiment.

[0048] In a non-represented alternative to the fourth alternative an actuator member having a similar shaft with two cylindrical portions and a fillet can cooperate in a closing member with a cylindrical tubular extension as it is on the first embodiment. In this alternative a superior compression value of the O-ring is only achieved when the shaft translates to a downward extreme position, the O-ring being further compressed between the cylindrical bore and the fillet.

[0049] A fifth embodiment is represented in reference to figures 10 and 11. The shaft 24 is similar to the shaft of the third embodiment with a large portion 44, a narrow portion 46 and a filet 48 in-between. The tubular extension 32 of the closing member 18 is provided with an inner upper narrowing portion 36 similar as in the second and third embodiment and, also with an outer narrowing portion 50 arranged at the opposite end of the tubular extension 32. The O-ring is arranged in place between the two narrowing portions 36, 50.

[0050] In use, when the shaft axially translates, the O-ring rolls on the narrow portion 46 of the shaft and on the cylindrical bore 22 between said two narrowing portions 36, 50. When fuel pressure peaks occur, the O-ring deforms and it is pushed to get in a narrowing portion where it is further compressed.

[0051] A step of the assembling method is represented on figure 11. The O-ring has been firstly installed in the closing member 18, in the tubular extension between the two narrowing portions 36, 50 and, after said installation a second tool 116 having a large base plate 118 and a central tubular projection 120 similar to the first tool 112 is utilized. The closing member 18 is placed on said second tool 116, the tubular projection 120 being in contact with the O-ring and, the O-ring being engaged over the narrow portion 46 of the shaft. In a subsequent assembling step not represented, the closing member 18 is upwardly pushed inside the sleeve, said another tool 116 pushing the closing member while maintaining the O-ring in place. In this upward movement, the peripheral wall 30 of the closing member is press-fitted inside the sleeve 16.

[0052] As it has been described, the main principle of the present invention relies in the rolling movement of the O-ring when the shaft translates and also on the ability to accommodate further deformations and compressions of the O-ring when fuel pressure peaks occur. Several further embodiments of the sealing arrangement combining shafts and closing members described can be assembled depending on the final need of the application.

LIST OF REFERENCES

[0053] 

X

longitudinal axis

ID

inner diameter of the O-ring

OD

outer diameter of the O-ring

SD

shaft diameter

BD

bore diameter

C

chord of the groove

10

servo injector

12

actuator assembly

14

actuator member

16

sleeve

18

closing member

20

sealing arrangement

22

bore

24

shaft

26

O-ring

28

annular passage

30

peripheral wall of the closing member

32

tubular extension

34

annular groove on the shaft

36

narrowing portion of the tubular extension

38

lower edge of the groove

40

upper edge of the groove

44

large section portion

46

narrow section portion

48

fillet

50

outer narrowing portion

100

method to assemble the sealing arrangement

110

presentation step

112

first tool

114

upper annular face of the tool

116

second tool

118

base plate

120

central tubular projection

Claims

1. Actuator assembly (12) of a fuel injector (10), the actuator assembly (12) extending along the longitudinal axis (X), an end of said actuator assembly being provided with a shaft member (24) extending through a bore (22), the annular passage (28) between the shaft and the bore being sealed by an O-ring (26), the shaft, the bore and the O-ring defining a sealing arrangement (20) comprising an elastomeric O-ring (26) radially compressed in an annular passage (28) between a shaft (24) and a bore (22) extending along a longitudinal axis (X), the shaft (24), in use, reciprocally axially translating relative to the bore (22),
characterized in that
the sealing arrangement (20) is adapted to force the O-ring (26) to roll on the shaft (24) and on the bore (22) when the shaft (24) translates relative to the bore (22).

2. Actuator assembly (12) as claimed in the preceding claim wherein the shaft (24) is provided with an annular groove (34) in which is placed the O-ring (26), said O-ring (36) rolling, in use, between the two edges (38, 40) of the groove so that when the shaft ends a longitudinal translation the annular passage (28) restricts and the O-ring gets further compressed.

3. Actuator assembly (12) as claimed in any of the preceding claims wherein the bore (22) is provided with a narrowing portion (36) arranged at a first end of the portion of the bore (22) so that under the influence of fuel pressure peaks, the O-ring is further deformed and further compressed in said narrowing portion (36).

4. Actuator assembly (12) as claimed in claim 3 wherein the bore (22) is provided with a second narrowing portion (50) arranged at a second end of the portion of the bore.

5. Actuator assembly (12) as claimed in any one of the preceding claims further comprising a cylindrical sleeve (16) closed at an extremity by a closing member (18) having a wall defining the bore (22) through which extends the shaft (24); said wall further defining a conical peripheral (30) wall adapted to deform to be press-fitted inside the extremity of the sleeve.

6. Fuel injector (10) comprising an actuator assembly (12) as claimed in any one of the preceding claims.

7. Method (100) to assemble an actuator assembly (12) as claimed in any of the claims 1 to 5 wherein the method comprises the steps of:

a) providing an O-ring (26), a resilient closing member (18) and a servo actuator (14) arranged in a cylindrical sleeve (16); the closing member (18) defining a bore (22) adapted to receive the O-ring (26) and, the servo actuator (14) having a shaft (24) protruding out of the sleeve (16),

b) providing a tool (112, 116) having a tubular member adapted to engage in the annular passage (28), said tubular member defining an upper annular face (114);

c) positioning said upper annular face (114) in contact with the O-ring (26);

d) pushing the O-ring (26) inside the annular passage (28).

7. Method (100) as claimed in claim 6 wherein the shaft (24) is provided with an annular groove (34), the method (100) further comprising, before step d) the following step:

e) positioning the O-ring (26) around the shaft (24) in place in the groove (24) and wherein;

during step d) the tool (112, 116) ensures that the O-ring remains inside the groove (24).

8. Method (100) as claimed in any of the claims 6 or 7 wherein the tool (116) provided at step b) further comprises a base plate (118) adapted to receive the closing member (18), the tubular member projecting from the base plate and forming an integral centrally tubular projection (120); and wherein,
during step c) the closing member (18) is arranged on the base plate (118) of the tool (116) and is presented (110) in face of the cylindrical sleeve (16) and wherein,
during step d) the closing member (18) is press-fitted inside the sleeve (16), the O-ring (24) being pushed in place in the annular passage (28).

Drawing