Note: Descriptions are shown in the official language in which they were submitted.
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ECCENTRIC SEALED ROTARY DRIVE DEVICE, PARTICULARLY
FOR A POSITIVE DISPLACEMENT PUMP
FIELD OF THE INVENTION
The present invention relates to an airtight rotating driving device with
eccentricity, especially for volumetric pump, i.e. a driving device enabling
the
conversion of a rotary movement into a circular orbital movement, while
isolating with
an absolute and lasting airtightness, the parts carrying out the orbital
movement with
respect to those carrying out the rotary movement.
Such a driving device is already used in off centered or eccentric rotating
piston
volumetric pumps, and it will be described hereafter with reference to such a
pump,
being understood that this device may be used also for instance in eccentric
screw
volumetric pumps, or even may be mounted in order to make up a driving
assembly for
transmitting a rotating movement in a completely airtight way.
BACKGROUND OF THE INVENTION
For the application of the device according to the invention, to the driving
of an
eccentric piston volumetric pump, it is known that in this type of pump, a
circular
piston carnes out an orbital movement inside a cylinder bounded by two
circular walls
of different diameters. The diameter of the piston ranges obviously between
these two
diameters. The cylinder is provided with a wall enabling the isolation of the
exhaustion
and discharge chambers. The piston skirt is interrupted in the alignment of
this wall,
designated also as partition.
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The center of the piston has a circular rotating movement whereas the piston
does not revolve around itself, i.e. that the abscissa and ordinate axes
remain
permanently parallel to their initial orientation.
It is particularly interesting to have available an airtight and non-rotatable
sleeve,
designated hereafter as « sleeve », around the shaft and all along the whole
length of the
shaft. The main advantage of such a rotating piston pump with a non-rotatable
airtight
sleeve, is its absolute airtightness as opposed to other rotating pumps which
always
require a rotating airtight means (for instance, packing, lipped joint or
mechanical
gasket).
Another solution to this rotatable airtightness problem consists in a magnetic
driving, but this latter has the drawback of not being applicable to all the
products
which have to be pumped and especially of being expensive.
The solution used heretofore consists in associating to the eccentric piston
an
elastomer airtight sleeve provided internally with an intricate device, which
enables
ensuring the conversion of a rotating movement into an orbital movement.
However, apart from the complexity of the internal device of the sleeve, this
solution which uses an elastomer sleeve presents a certain number of
limitations related
to:
-temperature withstand;
-mechanical withstand;
-resistance to pressure differences;
-chemical compatibility with certain products;
-compliance to food standards.
Thus attempt has been made for achieving a stainless steel sleeve. However, it
is
known that stainless steel bellows and diaphragms can absorb axial distortions
and
angular distortions but that they present a close limitation to radial
distortions.
Yet, the principle of operations of the volumetric pump with rotating piston
requires inherently a strictly radial distortion at a frequency or angular
velocity ranging
from 50 to 1000 rpm.
Heretofore, the only possible solution would have led to a considerable
lengthening of the bellows, this being incompatible with the overall
dimensions
required, with the hydrodynamic effects and with the distortion due to the
weight of the
bellows itself.
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SUMMARY OF THE INVENTION
The researches which have led to the present invention enable to cope with the
above mentioned drawbacks, and to solve the problems considered by providing
an
airtight rotatable driving device with improved eccentricity which can be used
in a
volumetric pump with a rotating piston.
Generally, according to the invention, the airtight rotatable driving device
with
eccentricity, especially for volumetric pump is of the type comprising a shaft
having an
input section, rotatably supported by a fix bearing and rigidly linked to a
rotating driving
means, and an output section the axis of which is parallel and off centered by
a distance d,
with respect to the input section, in such a way as to describe an orbital
circular
movement around the said input axis during the shaft rotation, and an airtight
sleeve
which can be distorted, mounted airtightly between two supporting input and
output
flanges surrounding rotatably the two opposed input and output shaft ends
respectively.
According to one essential characteristic of the invention, the shaft
comprises an
intermediate sloped section, arranged between the input and output sections,
the axis of
which is directed according to an angle a with the parallel input and output
axes, the
supporting input flange is rigidly linked to the fix bearing and the
supporting output
flange is associated to a pad which airtightly closes the sleeve and inside
which a roller is
locate inside a recess, the said roller being associated to the output
section, the
non-rotatable sleeve being made up of two metallic bellows airtightly
connected by means
of a guiding ring mounted slidingly in a longitudinal direction on the
intermediate shaft
section, in such a way as any shearing radial distortion of the non-rotatable
sleeve is
converted into a simple compression-expansion angular distortion of each one
of the
bellows, each directrix of each bellows being forced to carry out an arc of a
circle.
According to other characteristics of the invention:
- the two metallic bellows are identical, preferably of the ringed or
corrugated type, and
are made of stainless steel, the guiding ring connecting the two bellows being
mounted longitudinally in sliding relation with a supporting ring fixed to the
sloped
intermediate section,
- the optimal value of the angle a is computed in such a way as the respective
axes of
the two metallic bellows, describe individually,
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during the rotation of the bent shaft, an arc of circle perpendicular to the
respective
terminal faces of the sleeve, the said arcs of circle being mutually tangent
at the terminal
faces located on each side of the linking and guiding ring, the said terminal
faces being
respectively common to the said ring and to the two bellows,
-the respective intersection points between the axes are located preferably at
half distance
between the two terminal faces of each one of the associated sleeves, so that
the slope
angle a of the intermediate section of the shaft is nearly equal to twice the
angle between
the input axis and the general direction of the section linking the center of
the input
terminal face and the center of the output terminal face of the sleeve.
Other characteristics and advantages of the invention will appear more clearly
from
the following description, made in relation with the enclosed drawing.
BRIEF DESCRIPTION OF THE DRAWING
The single Figure shows a schematic partial section view of a preferred
embodiment
of an airtight rotatable driving device with eccentricity according to the
invention, used by
I S way of example in a volumetric pump with an off centered rotatable piston.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the single figure, this latter shows schematically an airtight
rotatable
driving device with eccentricity, of the type comprising first a shaft
generally designated
by 1 and having essentially input section 2 and output section 3, with
circular cross section.
The input section 2 shows a shaft end 4 with a rotation axis 5. This shaft end
4 is
rigidly linked to a rotatable driving means not shown, and having generally
the same
rotation axis 5 as the said input section 2. Besides, the shaft end 4 is
rotatably supported by
a fix bearing 6, a conical roller or toggled bearing 7 being arranged between
the span 8 of
the shaft end 4 and the fix bearing 6.
In the same way, the output section 3 shows a shaft end 9 with a rotation axis
10,
parallel and off centered by a distance d with respect to the rotation axis 5
of the input
section 2, in order to describe a circular orbital movement around the said
input axis 5
during the rotation of the shaft 1. Besides, the shaft end 9 is rotatably
supported by a pad
which will be studied more in details hereafter, a roller bearing 12 being
arranged between
the said pad 11 and a bushing 13 surrounding the shaft end 9.
Furthermore, the pump comprises an airtight sleeve which can be
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distorted, generally designated by 14, and airtightly mounted between
big and small supporting flanges 15 or 16 rotatably surrounding the
two opposite shaft ends of the input 4 and the output 9 respectively of
the rotating shaft 1. More precisely, the big flange 15 can be held in a
5 fixed position, for instance by means of peripheral stud bolts, against
the fix bearing 6 of the input shaft end 4 whereas the small flange 16
may also be held, for instance by means of locking screws, against the
pad 11 which airtightly closes the sleeve 14, and which forms a
recessed housing, not shown, for .the roller bearing 12 supporting the
' bushing 13 of the output shaft end 9.
According to an essential feature of the invention, the shaft 1
comprises a sloped intermediate section 17, arranged between the input
section 2 and the output section 3, and the axis of which 18 makes an
angle a with the input axis 5 and the output axis 10. Besides, the sleeve
14 is made up of two metallic bellows 19 and 20, airtightly connected by
means of a guiding ring 21 mounted longitudinally in sliding relation on
the intermediate section I7 of the shaft 1. Under theses conditions, any
shearing radial distortion of the sleeve 14 is converted into a simple
compression-expansion angular distortion of each one of the bellows 19
and 20, each directrix of each one of the bellows being forced to carry
out an arc of circle.
According to the invention the two metallic bellows 19 and 20 are
generally identical and theoretically interchangeable and are of the
ringed or corrugated type. They are made up is stainless steel the
stiffness of which is such as the rotation of the shaft 1 does not drive
the terminal pad 11 of the sleeve 14, the input flange of which 15 is
alone is fix. Therefore, it is possible to suppress the intricate internal
device which was compulsorily provided in the elastomer sleeve- in order
to ensure the conversion of the rotating movement into an orbital
movement.
Besides, the guiding ring 21 linking the two metallic bellows 19
and 20 is mounted longitudinally in sliding relation with a supporting
ring 22 fixed to the intermediate slope section 17, a needle bearing 23
may be inserted between the supporting ring 22 and the guiding ring
21.
According to still another feature of the invention, the optimal
value of the angle a is computed in order that the respective axes 5, 18
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and 18, 10 of the two metallic bellows 19 and 20, each one describe,
during the rotation of the bent shaft 1, an arc of circle perpendicular to
the respective terminal faces 24 and 25 of the sleeve 14, the said arcs of
circles being mutually tangent at the terminal faces 26, 27 located on
each side of the linking and guiding ring 21 the said terminal faces 26
and 27 being respectively common to the ring 21 and to the two bellows
19 and 20.
On the other hand, again according to the invention, the
intersection points respectively 28, 29 between the arcs 5, 18 and 10
~ are preferably located at half distance between the two terminal faces
- 24, 26 and 27, 25 of each one of the associated sleeves or bellows 19
and 20. As a result the value of the slope angle a of the intermediate
section 17 of the shaft l, has approximately twice the value of the angle
between the input axis 5 and the general direction of the section, not
shown, linking the center 30 of the input terminal face 24 and the
center 31 of the output terminal face 25 of the sleeve 14.
Subsidiarily, the input section 2 is preferably slightly conical and
presents a decrease of diameter from the input shaft end 4, provided
with a cylindrical span 8 the axis of which is the input axis 5 of the
shaft 1, upto an escape bending 32 connecting the sloped intermediate
section 17, this latter presenting a circular cross-section of generally
constant diameter extending from the escape bending 32 connecting the
input section 2 and almost nearly the area of the output shaft end 9,
the axis of which is the output axis 10 of the shaft 1.
Besides, the sloped intermediate section 17 comprises an area 33
of a slightly increased diameter located at the intermediate part between
the respective intersection points 28, 29 of the sloped axis 18 of the
intermediate section 17 with the parallel input axis 5 and output axis
10, and which forms an intermediate span 33 on which is fixed the
supporting ring 22 of the guiding ring 21 linking the two metallic
bellows 19, 20 and mounted longitudinally in sliding relation with the
said supporting ring 22.
According to a possible utilisation of the invention, by inserting in
a recess a roller in the end 11 and by inserting in this roller the off
centered end of a crankshaft (or handle) an assembly is achieved
enabling the transmission of a rotating movement in an absolutely
airtightness condition.
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Referring once again to the single figure, this latter represents
schematically a preferred utilisation of the driving device according to
the invention in a volumetric pump with off-centered rotating piston.
As it is known, such a pump comprises first a fix cylinder,
generally designated by 34, and second, an off centered rotating piston,
mounted generally on the end of the sleeve I4.
More precisely, the fix cylinder 34 is made up of a fix cylindrical
body 38 mounted between two ring shaped fix supports 39 and 40, the
support 39 being rigidly linked to the fix bearing 6 supporting the input
' section 2 of the shaft 1, the support 40 of the said body 38 being
associated to the cylinder 34 of the pump, the piston of which is rigidly
linked to the pad 11 which airtightly closes the sleeve 14 and which is
supported by the end of the output shaft 9 having a circular orbital
movement.
The product which has to be pumped, which may be liquid, fluid or
viscous, is located especially between the non-rotatable sleeve I4 and
the internal wall 35 of the fix cylinder 34 and moves freely between the
inlet area 36 and the exhaust-discharge area 37.
The exhaust-discharge area 37 or the actual pumping area is
located beyond the pad 11 which airtightly closes the sleeve 14 and
comprises exhaust and discharge chambers, separate from the cylinder
34 by a partition wall, the end of the off centered piston with a circular
orbital movement comprising a skirt interrupted at the alignment with
the said partition wall or diaphragm; these known elements are not
shown fox sake of clarity.
As mentioned hereabove, the driving device according to the
invention is located in the cylindrical body 38 of the pump; the big
flange 15 which supports the sleeve 14 could be held in a fix -position,
by means of the said stud bolts, between the fix bearing 6 of the end of
the input shaft 4 and the ring-shaped support 39 of the cylinder 34.
According to another possible utilisation of the invention, the
driving device is mounted in a volumetric pump with an off-centered
screw, not shown. Such a pump comprises generally an off centered
helical screw or rotor, with a single tooth, rotating in a double teeth
helical stator, the rotation generating closed volumes moving axially
from the exhaust to the discharge. Under such conditions, the pump
stator is associated directly or indirectly to the fix bearing 6 supporting
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the input section 2 of the shaft 1, whereas the off-centered rotor helical
screw is associated to the pad 11 and to the output end shaft 9 having a
circular orbital movement.
Obviously, the present invention is described and represented only
by way of non limitative explanation and any useful modification can be
brought thereto, especially in the field of solutions technically
equivalent, without departing from the scope of the invention.
