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
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).