Note: Descriptions are shown in the official language in which they were submitted.
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FANWHEEL ATTACHMENT USING EXPANSION¨TOLERANT CONICALLY
TAPERED RINGS
TECHNICAL FIELD
The present invention relates to the general field of
assembling a part that is of the wheel type onto a shaft or
other member having an axis of rotation, and in particular
to assemblies of this type that are designed to be exposed
to high thermal operating stresses, and more particularly
to high temperatures and/or to high temperature gradients.
The present invention relates more particularly to a
device designed to drive a fluid in motion or to be driven
by a fluid in motion, such as a fan, a pump, or a turbine,
said device including at least one wheel that is designed
to co-operate with said fluid in order to drive it or to be
driven by it, said wheel being fastened to a shaft, itself
mounted to move in rotation about an axis of rotation, the
wheel being fastened to the shaft by being clamped between
first and second thrust members that are retained by said
shaft and that are urged axially towards each other.
The present invention also relates to a method of
assembling a wheel onto a shaft that is mounted to move in
rotation.
PRIOR ART
Various mechanical mounting solutions are well known to
the person skilled in the art when it is necessary to
assemble a mechanical part, and more particularly a wheel
onto a shaft in order to constrain the two parts to move
together in rotation and/or in translation, and thus enable
torque to be transmitted from the wheel to the shaft or
vice versa.
Among the known solutions, there exist, in particular,
force-fitting or hot interference fitting, making it
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possible to force a shaft into the hub of the wheel with
the diameter of the shaft being slightly greater than the
diameter of the bore in said hub, the assembly thus being
held tight by the stresses resulting from the deformation
of the parts, and more particularly their elastic radial
deformation.
Assemblies on spindles are also known in which the
shaft has a slightly inclined support span so as to enable
a conical hub of complementary shape to be fitted over it,
and pressed endwise by a bolt or by a nut.
The very shallow conical taper of the elements enables
the wheel to fit over the spindle substantially over the
entire length of the hub, while preserving a thrust surface
that extends over the entire bore of the hub and that makes
it possible to subject said wheel to essentially radial
clamping stress, and the larger the holding force that
compresses the wheel against the spindle the higher the
essentially radial clamping stress.
Although such assembly methods are generally
satisfactory, they suffer from certain drawbacks.
Firstly, they systematically generate high stresses in
the assembled parts.
In particular, the centrifugal radial stresses that are
exerted on the hub and the resulting tangential stresses
can, in certain situations, and in particular when
excessive clamping is applied on assembly, cause fatigue,
deformation, or indeed splitting apart by said hub
cracking.
In addition, such assemblies are particularly sensitive
to the consequences of thermal expansion phenomena that
occur in uses in which said assemblies are subjected to
high temperatures or to high temperature gradients.
This applies in particular when the assembly is
incorporated into a device designed to be immersed in a
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fluid that is particularly hot, or that is subjected to
large and/or rapid variations in temperature, e.g. gases
from a burner, from a blast furnace, or from an industrial
furnace.
Depending on whether the shaft tends to expand radially
to a larger extent or, conversely, to a smaller extent than
the hub of the wheel, then either excessive clamping is
observed, which can deform the hub plastically or even
split it apart, or else relaxing of the clamping is
observed, which can lead to the wheel slipping relative to
the shaft, thereby preventing normal transmission of the
torque between the two elements.
Axially, such differential expansion can cause warping
by buckling of the shaft or of the hub of the wheel, such
deformations causing imbalance resulting in vibration that
adversely affects operation of the assembly as a whole.
SUMMARY OF THE INVENTION
Objects assigned to the present invention are therefore
to remedy the above-mentioned drawbacks and to propose a
novel device designed to drive a fluid in motion or to be
driven by a fluid in motion, and in which the assembly of
the wheel onto the shaft is particularly robust, reliable,
and insensitive to phenomena of expansion of the parts, in
particular when they operate at high temperatures, or at
high temperature gradients.
Another object assigned to the invention is to propose
a novel device of structure and of operation that are
particularly stable and balanced.
Another object assigned to the invention is to propose
a novel device that is resistant to wear and that offers
excellent longevity.
Another object assigned to the invention is to propose
a novel device having behavior, in particular in the event
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4
of exposure to large temperature variations, that is
particularly predictable, controllable, and reversible.
Another object assigned to the invention is to propose a
novel device that is of structure that is simple and
reliable, and in which manufacture, assembly, and maintenance
are particularly quick and easy, and as inexpensive as
possible.
Another object assigned to the invention is to propose a
novel device that is particularly strong and in which assembly
remains functional, safe, and friendly to the parts,
regardless of the operating conditions, both under transient
conditions and under steady-state conditions.
Another object assigned to the invention is to propose a
novel device in which assembly is reversible and the component
parts are readily removable and replaceable.
Another object assigned to the invention is to propose a
novel device that makes it possible to transmit high torque
between the wheel and the shaft.
Finally, an object of the present invention is to
propose a method of assembling a wheel on a shaft that
guarantees that the wheel is secured to the shaft
effectively and in manner that is friendly to the parts,
while also not being affected by expansion phenomena.
Certain exemplary embodiments can provide a device
designed to drive a fluid in motion or to be driven by a fluid
in motion, said device including at least one wheel that is
designed to co-operate with said fluid in order to drive said
fluid or to be driven by said fluid, said wheel being fastened
to a shaft, said shaft mounted to move in rotation about an
axis of rotation, the wheel being fastened to the shaft by
being clamped between first and second thrust members that are
retained by said shaft and that are urged axially towards each
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other, wherein the first thrust member has, against the wheel,
a first thrust surface that is substantially conical and that
is substantially carried by a first generator cone having a
vertex or "first focus" pointing towards the second thrust
member with a half-angle at the first focus being greater than
an angle of adhesion corresponding to a coefficient of
friction between said first thrust surface and the wheel, and
wherein the second thrust member has, against the wheel, a
second thrust surface that is substantially conical, that is
disposed in opposition relative to the first thrust surface,
and that is substantially carried by a second generator cone,
having a vertex or "second focus" pointing towards the first
thrust member, with a half-angle at the second focus being
greater than or equal to an angle of adhesion corresponding to
a coefficient of friction between said second thrust surface
and the wheel, and where the first focus and the second focus
substantially coincide.
Certain exemplary embodiments can provide a method of
assembling a wheel designed to co-operate with a fluid to
drive said fluid or to be driven by said fluid onto a shaft
that is mounted to move in rotation about an axis of rotation,
said method comprising: clamping said wheel between first and
second thrust members that are urged axially one against the
other, the first thrust member having, against the wheel, a
substantially conical first thrust surface that is
substantially carried by a first generator cone having a
vertex or "first focus" pointing towards the second thrust
member, with a half-angle at the first focus being greater
than or equal to an angle of adhesion corresponding to a
coefficient of friction between said first thrust surface and
the wheel, the second thrust member having, against the wheel,
a substantially conical second thrust surface that is
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5a
substantially carried by a second generator cone having a
vertex or "second focus" pointing towards the first thrust
member, with a half-angle at the second focus being greater
than or equal to an angle of adhesion corresponding to a
coefficient of friction between said second thrust surface and
the wheel, and where the first focus and the second focus
substantially coincide.
Other embodiments provide a device designed to drive a
fluid in motion or to be driven by a fluid in motion, such as
a fan, a pump, or a turbine, said device including at least
one wheel that is designed to co-operate with said fluid in
order to drive it or to be driven by it, said wheel being
fastened to a shaft, itself mounted to move in rotation about
an axis of rotation (X-X'), the wheel being fastened to the
shaft by being clamped between first and second thrust members
that are retained by said shaft and that are urged axially
towards each other, said device being characterized in that
the first thrust member has, against the wheel, a first thrust
surface that is substantially conical and that is
substantially carried by a first generator cone having its
vertex or "first focus" pointing towards the second thrust
member with the half-angle at its vertex being greater that
the angle of adhesion corresponding to the coefficient of
friction between said first thrust surface and the wheel.
Other embodiments provide a method of assembling a wheel
designed to co-operate with a fluid to drive said fluid or to
be driven by it onto a shaft that is mounted to move in
rotation about an axis or rotation (X-X'), said method being
characterized in that it includes a clamping step during which
the wheel is held stationary on the shaft of clamping said
wheel between first and second thrust members that arc urged
axially one against the other, the first thrust member having,
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against a wheel, a substantially conical first thrust surface
that is substantially carried by a first generator cone having
its vertex or "first focus" pointing towards the second thrust
member with the half-angle at its vertex being greater than or
equal to the angle of adhesion corresponding to the
coefficient or friction between said first thrust surface and
the wheel.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, characteristics and advantages of the
invention appear in more detail on reading the following
description, and from the accompanying drawings, given
merely by way of non-limiting illustration, and in which:
. Figure 1 is a partially cutaway fragmentary
perspective view showing a variant embodiment of a device of
the invention of the fan type;
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= Figure 2 is a side diagram showing the principle of
dimensioning the conical taper of the thrust member of the
invention;
= Figure 3 is a fragmentary view in axial section
showing the device of Figure 1;
= Figure 4 is a diagram showing the operating principle
enabling the assembly of the invention to accommodate
expansion and to go from a contracted configuration to an
expanded configuration;
= Figures 5 to 9 are axial section views showing a
plurality of possible configurations for thrust members in
devices of the invention;
= Figure 10 is a diagram showing the effects of
modifying the focuses of the thrust members, when the
coefficient of linear expansion of the shaft is less than
that of the wheel;
= Figures 11 and 12 are fragmentary views in
longitudinal section showing the interference and
separation phenomena corresponding to the effects explained
in the diagram of Figure 10.
= Figure 13 is a partially cutaway fragmentary
perspective view showing an example of a device of the
invention being assembled;
= Figure 14 is a diagram in a fragmentary side view,
showing the wedging phenomenon of a coupling key;
= Figure 15 is an axial section view showing a variant
embodiment of a device of the invention including two
stepped bi-conically tapering thrust members, having
focuses that coincide; and
= Figure 16 is a geometrical diagram showing the
principle of the effect on the assembly of a difference
between the real expansion focus and the focus of the
thrust member in question, when, for example, the increase
in temperature is substantially uniform between the shaft
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and the wheel while the coefficient of linear expansion of
the shaft is greater than the coefficient of linear
expansion of the wheel.
BEST MANNER OF IMPLEMENTING THE INVENTION
The present invention relates to a device 1, of the
rotary machine type, including at least one wheel 2
fastened to a shaft 3, said shaft being itself mounted to
move in rotation, e.g. on bearings (not shown), about an
axis of rotation (X-X'), said device 1 requiring coupling
between said wheel 2 and said shaft 3 that is sufficiently
stable and strong to enable at least transmission of drive
torque between these two elements about said axis of
rotation (X-X').
More particularly, said device 1 is designed to be
exposed to a fluid, and preferably immersed therein, so
that it can either drive said fluid in motion, the wheel 2
being driven by the shaft 3 so as to generate a fluid
stream V, it then being possible for said device 1 to
constitute a fan, a circulator, an extractor, a pump, etc.,
or be driven by said fluid in motion, the wheel 2
collecting the energy from the fluid stream V to drive the
shaft 3 in rotation, it then being possible for the device
1 to constitute, for example, a generator of the turbine
type that is propelled by wind, water, or marine currents,
etc.
Naturally, the device 1 may be arranged to generate or
to collect a fluid stream V that may either be
substantially linear and preferably substantially parallel
to the axis of rotation (X-X'), so as to approach the wheel
head-on, as in the variants shown in the figures, or so as
to approach the device in a manner substantially transverse
to the axis (X-X') and preferably substantially tangential
to the wheel.
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Naturally, the wheel 2 is designed to co-operate with
said fluid in order to drive it or to be driven by it, said
wheel 2 preferably having, for this purpose, a plurality of
blades 4 connected to a central hub 5, said hub being
provided with a bore 6 enabling it to be engaged over the
shaft 3.
In order to guarantee the mechanical cohesion between
the shaft 3 and the wheel 2, said wheel 2 is fastened to
said shaft 3 by being clamped between first and second
thrust members 10, 11, said first and second thrust members
10, 11 being retained by the shaft 3, the thrust members
advantageously having the axis of rotation (XX') passing
through them and being urged axially towards each other.
The wheel 2 is thus advantageously maintained by
clamping, by being compressed between said first and second
thrust members 10, 11, which members preferably come to
exert their action in contact, preferably exclusively, with
the edge faces of the hub 5 on either side thereof.
Naturally, the assembly of the invention may be adapted
depending on the level of torque to be transmitted between
the wheel 2 and the shaft 3, regardless of whether said
torque results from steady-state rotary drive or from
inertia phenomena related to the masses of and to the
speeds of rotation of the parts (in particular of the wheel
2) during acceleration or braking stages.
Thus, although it is predictable that the maximum
torsional moment that tends to cause the wheel to pivot
about the shaft will be low, e.g. when the device is a
lightweight device rotating at moderate speed and not
exposed to sudden accelerations or stops, it is not
impossible that the wheel 2 will be blocked by losing its
degree of freedom to rotate about the shaft 3 merely as a
result of the opposing axial clamping from the thrust
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members 10, 11, by friction under stress between the wheel
2 and each of said thrust members 10, 11.
Optionally, the geometrical shape of the thrust members
10, 11, the choice of the component materials of the parts,
and the intensity of the axial clamping force exerted by
them on the wheel 2 are adapted accordingly.
However, in particularly preferred manner, the axial
clamping between the thrust members is aimed mainly, or
indeed almost exclusively, at keeping the axes of the wheel
2 and of the shaft 3 substantially in coincidence, the
assembly that results merely from clamping by urging the
thrust members 10, 11 axially towards each other being
designed to withstand the lateral forces, of the dynamic
imbalance type, that might cause the wheel 2 and/or the
shaft 3 to move radially, while the device may also include
auxiliary coupling means 40, e.g. comprising one or more
keys, as described in detail below, said coupling means 40
being designed to reinforce the assembly and to transmit
torque, optionally very high torque, e.g. approximately in
the range 1000 (one thousand) newton meters (N.m) to 10,000
(ten thousand) N.m, from the shaft 3 to the wheel 2 (or
vice versa).
Naturally, it is possible to secure the wheel 2 to the
shaft 3 while removing substantially any degree of freedom
between these elements, in particular by preventing any
relative movement in rotation about the axis (X-X'), and
also, preferably by preventing any relative movement in
translation of the wheel as a whole along said axis.
The first and second thrust members 10, 11 may
naturally be retained on the shaft 3, advantageously in
separate manner, by any suitable means designed to prevent,
or at least to limit them moving apart relative to each
other, and therefore to prevent or at least to limit
loosening of the wheel, said thrust members being, for
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example, formed by separate removable elements mounted on
the shaft, such as threaded rings.
However, preferably, at least one of the thrust
members, and, by convention below, the second thrust member
5 11 is formed integrally with the shaft 3, and, for example,
is machined or forged to form a shoulder that may be
straight (collar) or inclined (frustoconical).
Advantageously, the continuity of the material
guarantees the strength and permanence of the thrust
10 procured by said thrust member 11, while removing any risk
of play. It also procures a reference abutment that
simplifies mounting the wheel on the shaft and that
optionally guarantees that assembly is reproducible.
In accordance with an important characteristic of the
invention, the first thrust member 10 has, against the
wheel, a substantially conical first thrust surface 12 that
is substantially carried by a first generator cone C12
having its vertex F12 or "first focus" pointing towards the
second thrust member 11, and having the half-angle at its
vertex a12 greater than or equal to the angle of adhesion
912/2 corresponding to the coefficient of friction between
the first thrust surface 12 and the wheel 2.
Advantageously, such a conical taper makes it possible
substantially to maintain the clamping force of the first
thrust member 10 against the wheel 2, and more particularly
the axial load component of said clamping force, while
also, in the event of dimensional variation of the wheel 2
relative to the shaft 3 and/or relative to the first thrust
member 10, e.g. under the effect of thermal expansion,
allowing the wheel to slide along the first thrust surface
10, at the contact interface created and maintained by the
axial load between said wheel 2 and said first thrust
member 10.
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11
In other words, the first generator cone C12 is more
open than the adhesion cone associated with the pair {first
thrust surface 12; wheel 2}, as shown in Figure 2, so as to
enable the assembly to accommodate any dimensional
variations in these parts.
The term "angle of adhesion", generally referenced T in
Figure 2, designates the angle of inclination, relative to
the normal to the thrust surface 12, of the reaction R of
the support that, due to the existence of friction, opposes
any relative movement of the wheel 2 by sliding on said
thrust surface.
The coefficient of friction corresponds to the tangent
of said angle of adhesion T, i.e. to the ratio of the
tangential component T to the normal component N of the
reaction R of the support.
It can readily be understood that, in order to avoid
the parts jamming by chocking or seizing, i.e. in order to
allow the wheel to slide relative to the first thrust
member 10 (or conversely, to allow the thrust member,
carried by the shaft, to slide relative to the wheel), e.g.
under the effect of radial shrinkage FR of the hub 5, or,
conversely, of radial expansion of the shaft and of the
first thrust member 10, it is necessary for the angle of
inclination of the thrust surface 12 relative to the axis
of rotation (XX'), i.e. the half-angle at the vertex
(referenced a in Figure 2) of the corresponding generator
cone, to be sufficiently large, and in particular greater
than or indeed much greater than said angle of adhesion (1).
In addition, in analogous manner, the half-angle at the
vertex a is advantageously less than or equal to the angle
complementary to said angle of adhesion , i.e. less than or
equal to 2- 9-
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12
This configuration makes it possible to guarantee the
possibility of relative sliding movement of the wheel on
the thrust surface 12 to accommodate axial stresses, e.g.
if the hub 5 expands, thereby exerting on the shaft 3, via
the thrust members 10, 11, a traction force or, conversely,
if the shaft contracts, thereby compressing the hub 5.
Thus, the half-angle at the vertex a, a], of the
generator cone lies substantially within the range [amTN,
amAx] where a,N is greater than or equal to, or indeed is
strictly greater than T, and amAx is less than or equal to,
or indeed is strictly less than 2 - T.
Advantageously, these constructional provisions enable
the device, and more particularly the subassembly formed by
the wheel assembled onto the shaft to accommodate
dimensional variations in its component parts, and in
particular the effects of differential volume expansion of
said parts.
As shown in Figure 4, the dimensional variations, both
axial and radial, that accompany going from a contracted
configuration shown in uninterrupted lines to an expanded
configuration, shown In dashed lines, are absorbed by the
relative movement, and more particularly by the relative
sliding of the contact surface of the hub 5 over and along
the first conical thrust surface 12, without causing any
destructive excess stress.
To be safe, instead of setting the conical taper limits
%AIN t CXMAX as a function of the exact value of the angle of
adhesion T, it is possible to set them as a function of a
value that is strictly greater than said angle adhesion,
e.g. greater than or equal to 2 x T, or indeed greater than
or equal to 3 x T. Applying such safety factors makes it
possible to ensure that the contact interface between the
wheel 2 and the thrust member 10 is sufficiently steeply
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13
inclined, regardless of the stress direction, to guarantee
that functional slip appears under all predictable
operating conditions, and in particular to guarantee that
the relative movement of the parts in the "go" direction
(expansion) and in the "return" direction (contraction) is
reversible.
Optionally, the reference angle of adhesion T is
considered to be the value corresponding to the predictable
maximum of the coefficient of friction value(s) that can
occur during operation of the device, which values can, in
particular, depend on the predictable surface state, and in
particular wear, of the parts, and on operating
temperature.
Although it is possible to make provision to use a
lubricant, between the wheel and the first thrust member,
e.g. a high-temperature lubricant of the graphite-copper
solid lubricant type, it is the dry coefficient of friction
that is preferably taken into account in order to determine
the thrust taper angle.
As shown in Figure 5, and subject to such an
arrangement being compatible with the required accuracy as
regards making the axes of the wheel and of the shaft
coincide, and with the wheel 2 being held radially and more
generally with the behavior of the device 1 in the face of
dynamic radial stresses, it is possible for the second
thrust member to form merely a shoulder that is
substantially radial, i.e. that is not inclined relative to
the axis, with only the first thrust member having a
conical shape making it capable, on its own, of
accommodating expansion.
Geometrically, such an arrangement can be considered as
corresponding to a situation in which the second thrust
member 11 has a thrust surface carried by a generator cone
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14
that is substantially flattened, of half-angle at the
vertex equal to n/2.
In such a situation, the first focus F12 is then
preferably axially situated substantially, or indeed
exactly, in register with said shoulder.
However, in particularly preferable manner, the second
thrust member 11 has, against the wheel 2, a second thrust
surface 13 that is substantially conical, that is opposite
relative to the first thrust surface 12, and that is
substantially carried by a second generator cone C13, having
its vertex F13 or "second focus" pointing towards the first
thrust member 10, and having the half-angle at its vertex
cen greater than or equal to, or indeed strictly greater
than, the angle of adhesion p13/2 corresponding to the
coefficient of friction between said second thrust surface
13 and the wheel 2.
The first thrust member and the second thrust member
can thus form frustoconical elements that penetrate in
opposite directions into the hub 5, preferably by coming to
bear respectively against first and second reentrant seats
14 and 15 that are substantially complementary to the shape
of the first and second thrust surfaces, and more
particularly substantially frustoconical. Contact is
preferably end-on surface-on-surface contact in order to
procure stable thrust and clamping pressure distributed
over a large load-bearing surface area, and in a manner
that is substantially uniform all the way around the axis
of rotation.
Advantageously, putting in place a carrying and
clamping system of the "X-shaped" bi-conically tapering
type facilitates centering the hub 5 on the shaft 3, and
therefore balancing the wheel 2, while also distributing
the absorption of the dimensional variations on either side
of the wheel, each thrust member 10, 11 being capable of
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absorbing its share of expansion by allowing the wheel to
move locally relative to its thrust surface 12, 13, thereby
ensuring that the assembly behaves uniformly, reproducibly,
and reliably.
5 Preferably, the first and second focuses F12, FiA lie
axially between the first thrust surface 12 and the second
thrust surface 13.
In other words, the "focal distance" of each generator
cone 012, CA is preferably less than or equal to the support
10 span of the shaft d3 lying axially between the contact zone
in which the wheel 2 is in contact with the first thrust
member 10 and the contact zone in which said wheel 2 is in
contact with the second thrust member 11, said support span
defining the segment of the shaft 3 in which axial and/or
15 radial dimensional variations can affect the assembly, and
in particular the stress state of the wheel.
Preferably, the half-angle at the vertex a32 of the
first generator cone 012, or, respectively, the half-angle
at the vertex a13 of the second generator cone Cn, lies
substantially in the range 30 to 60 , and preferably lies
in the range 40 to 50 , or indeed is substantially equal
to 45 .
Advantageously, in addition to facilitating relative
sliding of the parts, such a provision, makes it possible
to apply to the wheel 2 a clamping force that is
particularly well proportioned and in which the working
axial compression component can be particularly high and
easy to adjust, while, proportionally, its radial component
remains moderate.
Naturally, the characteristics of the second thrust
member 11 can be deduced mutatis mutandis and independently
from one another from all or some of the characteristics of
the first thrust member 10.
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In addition, in order to guarantee the device is
balanced and in order to avoid imbalance and vibration,
said device, and more particularly the shaft 3, the wheel
2, the thrust members 10, 11 and more generally the
assembly are preferably bodies of revolution, or at least
are invariant in rotation, about the axis (X-X').
Advantageously, the first generator cone C12 is
centered on the axis of rotation (X-X'). Advantageously,
the second generator cone C13 is also centered on the axis
(X-X').
More particularly, the first and second generator cones
C12, C13 are advantageously in mutual alignment and centered
on the axis of rotation (X-X'), their respective focuses
being situated on said axis.
The conical tapers of the first and of the second
thrust members, and the configurations of the first and of
the second focuses F12, F13, may have variations, as shown,
in particular as shown in Figures 5 to 9 without going
beyond the ambit of the invention.
Preferably, as shown in Figures 6 and 7, the first
focus F12 and the second focus F13 substantially coincide.
In other words, the first and second generator cones
C12, C13 preferably converge towards a common vertex.
In this way, the sum of their respective focal
distances d12, d13, each equal to the height measured axially
between the vertex of the cone and the base plane
intersecting the axis of rotation (X-X') and containing the
base ring marking the axially innermost contact made by the
huh 5 against the first and second thrust surfaces 12, 13,
respectively, is advantageously substantially equal to the
support span d3 of the shaft lying between said thrust
surfaces, i.e. d3 = d12+d13=
Advantageously, such a provision makes it possible, in
a manner that is substantially exact, at least at constant
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temperature, or with slowly varying temperature, to
compensate for the expansion of the entire support span of
the shaft d3, i.e. to adapt the reaction of the device to
the exact dimensions of the assembly, both axially and
radially.
As shown, in particular in Figure 4, it can be observed
that, on either side of the focal plane PF, i.e. of the
plane that is normal to axis of rotation (X-X'), that
contains the focus(s) F12, Ffl in question, the tangent of
the half-angle at the vertex a12, al3, that corresponds to
the slope of the thrust surface 12, 13 in question, is
R
12
substantially equal to the ratio where R12 represents
the radius measured between the axis of rotation (X-X') and
the point at which the hub 5 meets the thrust surface 12,
and where d12 represents the axial distance of said point
from the focus.
Thus, regardless of the respective values of the
coefficients of linear thermal expansion of the shaft and
of the hub, whether they are equal or different, the
movement of any point of the seat 14 and of the hub 5
relative to the first thrust member 10, or conversely of
any point of the first contact surface 12 relative to said
first seat 14, takes place along said slope, so that the
wheel can slide locally along said first thrust member, by
moving up or down the slope, without interfering with said
thrust member and without, conversely, becoming detached
therefrom.
Therefore, it is advantageously possible to keep axial
clamping that is substantially constant and having stresses
that are neither too accentuated, nor too relaxed by
differential expansion effects.
As shown in Figure 4, if consideration is given to a
point A belonging to the hub that expands relative to a
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focus F12, F13 in question until it reaches a point A', the
axial component 8,, and the radial component SR of the vector
AA' are respectively proportional to the radius at which
said point A is situated relative to the axis of rotation
(X-X') and proportional to the axial distance of said point
A relative to the focal plane PF, said vector rlf" being
collinear with the generator line of the first cone a12
intersecting said point A.
Thus, the invention makes it possible to ignore
dimensional variations related to the linear differential
expansion between the shaft 3 and the wheel 2, in three-
dimensions, by means of conical thrust members 10, 11
having focuses that coincide on the axis of rotation and
that thereby define a common expansion focus from which all
of said dimensional variations, both of shaft and of the
wheel, radiate.
Accommodating these dimensional variations takes place
by relative sliding between the seats of the hub and the
thrust surfaces presented by the shaft, substantially
without modifying the positions of these components or
modifying the axial loading.
Preferably, in substantially analogous manner or indeed
in substantially symmetrical manner, the same applies at
the coupling between the opposite portion of the hub 5 and
the second thrust member, it thus being possible for the
wheel 2 to "swell" around the shaft 3 and then to return to
its initial position, or vice versa, it being possible for
the shaft 3 to expand or to contract in the hub, in
particular substantially as a dilatation relative to the
center of the support span d3, it being possible for the
principle shown in the diagram of Figure 4 to apply mutatis
mutandis to each interface between a thrust member 10, 11
and the wheel 2, and depending on the respective
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19
coefficients of expansion and on the respective
temperatures of each of the parts in question.
Ideally, the parts (wheel and corresponding thrust
member) thus move freely by surface sliding with friction
over the same slope predefined by construction, in one
direction (expansion) and in the other direction
(contraction), while inducing substantially no significant
increase nor any significant relaxing of the axial
compression working stress, thereby avoiding losing the
operating clamping without however exposing the assembly to
degradation by deformation or breakage.
By way of example, if consideration is given to
behavior of the parts as shown in Figure 4, applied to one
of the assembly configurations corresponding to Figures 3,
6, or 7, the hub 5 can, when it heats up, undergo a volume
expansion, both axially and radially, starting from a
contracted configuration (shown in uninterrupted lines in
Figure 4), and therefore become longer and wider while
seeing its corresponding dimensions increase relative to
the dimensions of the shaft and of the abutment members 10,
11 on which it rests.
The surface of the first seat 14 can move up the slope
of the first conical thrust surface 12 (leftwards in said
figures), or, respectively, the surface of the second seat
15 can move up the slope of the second thrust surface 13
(rightwards), it thus being possible for the axial ends of
the wheel to move apart freely from each other under the
effect of the expansion, in particular axially, each moving
away from the focal plane that corresponds to it,
optionally in a manner substantially symmetrical about the
same focal plane PF (Figures 3, 6, and 7), until said ends
reach a position corresponding to the expanded
configuration (shown in dashed lies in Figure 4), in which
said ends go beyond the gauge plane attached to the shaft 3
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and facing which they initially find themselves in the
contracted configuration.
Particularly preferably, as is shown in Figures 3 and
6, the focal plane PE may be substantially centered axially
5 on the support span of the shaft d3, and/or may
substantially coincide with the midplane of the wheel 2,
and more particularly of the hub 5, which midplane is
perpendicular to the axis of said wheel and subdivides said
wheel, or, respectively, its hub, substantially into two
10 equal halves.
In this configuration, the two generator cones C12, C13
are advantageously opposite via their vertices and have
angles at their vertices that are equal.
However, it is not impossible for the focal plane PE to
15 be offset towards one or the other of the thrust members
relative to the center of the support span d3 of the shaft
and/or relative to the midplane of the wheel, as is shown
in Figure 7, the first and second generator cones then
having angles at their vertices that are of distinct
20 values.
In other variant embodiments, the first focus F12 and
the second focus F13 may be remote from each other axially,
the first and the second generator cones C12, C13 being
either separate, as shown in Figure 8, so as to cover,
together, only a fraction of the total support span d3
between the first thrust surface 12 and the second thrust
surface 13, while allowing a non-covered fraction A' to
remain, or, conversely, as shown in Figure 9, overlapping
in such a manner as to cover redundantly at least a
fraction A- of said total support span d3.
The defocusing distance axially separating the first
focus from the second focus is referenced A (delta), said
distance being referenced either negatively A (delta
negative) to designate an interfering overlap of the
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21
generator cones, or referenced positively A+ (delta
positive) to designate that said cones are disunited. When
A is zero, the focuses coincide.
The provision consisting in choosing the focal
distance (s) dn, dn of the generator cone (s) C12, Cn in such
a manner that their cumulative value (or individual value
when only one of the thrust members is conical) is strictly
less than (delta positive) or, conversely, strictly greater
than (delta negative) the total support span d3, makes it
possible to facilitate either a phenomenon of under-
compensation, in which the relative expansion of the parts
is not sufficiently compensated and causes interference
between the wheel 2 and the thrust member 10, 11 in
question, or, conversely, a phenomenon of over-compensation
that tends to facilitate relaxing of the compression
constraints between the two parts, in the direction of
separation of the contact surfaces of said parts.
Advantageously, in the first above situation, the
clamping force is facilitated, in order to improve
penetration, centering, and stiffness of the blocking of
the wheel on the shaft.
Conversely, in the other above situation, if concern
exists that friction and phenomena of wear that are too
large might appear, attempts are made to minimize them by
reducing the contact pressures in order to avoid any
accidental binding or seizure of the wheel 2 on its thrust
members 10, 11.
The choice of focal length for the generator cones
depends on the desired behavior, and also on the respective
values of the coefficients of linear expansion of the wheel
2 and of the shaft 3, and finally on the thermal stress
conditions of the assembly.
Figure 10 diagrammatically shows these phenomena,
assuming that the coefficient of expansion of the wheel 2
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and more particularly of the hub 5, is greater than the
coefficient of expansion of the shaft 3, and that the
temperatures of the two elements are substantially
identical.
Naturally, it is quite possible, and indeed preferable,
for the coefficient of expansion of the component material
of the shaft to be greater than the coefficient of
expansion of the hub, and then, at identical temperature,
the phenomena described below are reversed, the reasoning
remaining analogous. The same could also apply, subject to
the coefficient of expansion values, if the temperature of
the shaft is very much higher than the temperature of the
wheel, e.g. because of said wheel cooling rapidly after a
long cycle of hot operation.
With reference to Figure 10, if consideration is given
firstly to the top portion of the figure, in which portion
the focal length of the first cone 012 is shorter than the
length Lo of the segment of the assembly that is affected by
the expansion (with, for example Lo = d3/2 in the variants
of Figures 6, 8 and 9), it can be observed, by
geometrically constructing the theoretical movement to
which an edge segment of the part lying between two points
A and B would be subjected, depending on whether said
points belong to the wheel 2 or, conversely, to the shaft
3, that, instead of causing neutral sliding, said expansion
causes interference 20, i.e. a virtual penetration of the
envelope of the wheel 2 into the envelope of the shaft 3,
as shown in Figure 11.
In practice, it can be understood that such a situation
could result in a major increase in the stresses in said
zone, or indeed in plastic deformation of the parts.
For reasons of clarity and for convenience of
description, the points respectively belonging to the wheel
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23
2 and the shaft 3 are respectively given the subscript 2
and the subscript 3.
In addition, when a letter designates a point of the
part in the contracted configuration of said part, the
prime symbol (') is added to the letter designating the
arrival point corresponding to the expanded configuration.
Geometrically, for example, the following vector
OA'3=0-Fa3xA71.0A3
relationship applies: where a3 represents
the coefficient of linear expansion of the shaft 3 and AT
represents the variation in temperature.
Conversely, when the focal length of the cone Cl2 is
greater than the length Lo of the segment that is affected
by the expansion, in such a manner that said cone converges
beyond the reference plane situated axially at said
distance Lo from the initial thrust of the wheel on the
thrust member, the expansion of the hub results in
separation 21 of said hub, the envelope of the wheel
tending to separate and to move away from the envelope of
the first thrust surface 12, as is shown in Figure 12.
Figure 16 shows another geometrical illustration of the
operating principle of the invention.
The physical focus of the conical thrust member 10 in
question is referenced Fp, the position of which point is
determined by construction, and the real focus of
expansion, from which point the expansion of the part in
question takes place, is referenced FR.
Reference LA, or respectively LB, designates the
straight line passing through the real focus FR and through
a point A, or respectively a point B, of the load-bearing
surface of the part in question (i.e. of the seat 14 of the
wheel 2 or of the thrust surface 12 of the thrust member
10, considered to be the same as the shaft 3, for reasons
of convenience), said point being situated at a radius RA,
or respectively RB from the real focus, and shifting by a
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value dRA, or respectively dRB, during the expansion.
Unless otherwise indicated, the same referencing
conventions as in the preceding example are used.
Reference aA, or respectively aB designates the angle
formed by the straight line LA, or respectively LB, and the
axis of rotation (X-X'), and reference Up designates the
half-angle at the vertex of the generator cone of the
thrust member lying between said axis (X-X') and the
generator line L.
Reference A/2 also designates the axial gap between the
physical focus Fp and the real focus FR, it being possible
advantageously for said gap to correspond to the defocusing
half-distance defined above, if it is considered that the
real focus in question is situated half-way between the two
physical focuses corresponding to the physical focuses of
the thrust members 10, 11, and more particularly in the
midplane of the wheel.
When the gap A/2 is zero, FR coincides with Fp, and
thus the angles aA and a, (or respectively aB and Up) are
identical (the system is almost perfectly focused). The
real expansion then takes place by exact sliding of the
surfaces of the wheel 2 and of the thrust member along the
straight line LA, coinciding with the straight line LB and
the generator line Lp of the generator cone. The slope of
the thrust surface thus accommodates exactly and
proportionally the axial component and the radial component
of the expansion.
When said gap A/2 is not zero, the system is defocused
and the angles aA and Up are different. The ratio between
the real axial expansion and the real radial expansion then
no longer corresponds to the theoretical ratio offered by
the thrust member, the effective axial accommodation
capacity of the assembly then no longer being the same as
the radial accommodation capacity.
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Reference VR designates the "knocking value"
corresponding to the (normal) distance that theoretically,
after expansion, separates the contact surface 12 from the
seat 14, which distance is positive in the event of
5 separation and negative in the event of interference.
However, such knocking represents a virtual phenomenon
that can advantageously be compensated by implementing a
compensation system 25 as described below, it then being
possible for interference, as in Figure 11, to result in
10 the moving first thrust member 10 moving backwards axially
(away from the second thrust member) with an increase in
the initial axial elastic loading, and, conversely, it
being possible for an increase in play, as shown in
Figure 12, to result in said first thrust member 10 moving
15 forwards, with a reduction in said initial axial elastic
loading.
The knocking value VR is proportional to the difference
between the respective linear expansions of the parts and
the distance W corresponding to the length of the segment
20 that is orthogonally lowered from the real focus FR on the
generator line Lp of the thrust member (counted positively
in this example when the focal length of the thrust member
is shorter than the real focal length).
With reference to Figure 16:
25 For the shaft 3:
UA = dRA3 X sin (ap - aA)
(a3 x AT3 x RA) x sin (ap - aA) = a3 x AT3 x w
and:
UR = dRR3 X sin (ap - )
= (a3 x AT3 x RB) x sin - aB) = a3 x AT3 x
For the wheel 2:
VA = dRA2 x sin (ap - aA)
=(a2XAT2XRA)xsin(ap-aA)=a2xAT2xljI
and:
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26
VB = dRB2 X sin (ap - aB)
= (a2 2T2 x RB) x sin (ap - aB) = a2 x AT2 x
hence:
VR = Up - VA = UB VB - ( a 3 x AT3 - a2 x T2)A x
In the example shown in Figure 16, in which it is
considered, in particular that a3 > a2 (and more
particularly that a3 = 3 x a2), since each expansion of the
parts undergoes a temperature variation that is
substantially equal (AT3 =AT2) this leads to separation of
the shaft and of the hub 5.
If necessary, in the radially innermost portion of the
thrust member 10 connecting the operating thrust surface 12
to the central body 10' of said thrust member, it can be
advantageous to provide an optionally rounded setback 10"
that makes it possible to preserve a central body that is
relatively solid, strong, and stable, while also allowing
the wheel 2 to come into contact with said thrust surface
12, even if said thrust surface is of small dimensions, and
to move relative to said thrust surface.
The inventors have also observed that, although
implementing conical thrust members 10, 11 advantageously
enables the system to self-adapt to accommodate the
relative dimensional variations between the parts, and, in
particular the relative dimensional variations of the wheel
and of its hub 5 relative to the shaft 3 and to the thrust
members 10, 11, in particular under steady-state
conditions, during which each part is exposed to a
substantially uniform temperature, it could be useful to
perfect this adaptation capacity in order to procure finer
regulation of the clamping, or indeed in order to maintain
axial clamping that is substantially constant also when the
device is subjected to rapid temperature variations that
generate thermal gradients within the same part.
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It can easily be understood that, on a support span d3
in question, the shaft 3, or respectively the hub 5, may
present an internal temperature gradient, e.g. between its
outer portions that are the most exposed to hot fluid, and
its colder core, or, conversely, between certain outer
segments that are cooled more rapidly by applying a cold
fluid while the core of the shaft is still hot, or finally
between an upstream portion exposed to admission of the
fluid, and a downstream portion that is cooled at the
exhaust.
So long as the temperature is not uniform and is not
stabilized over the entire support span, each portion of
the shaft, and respectively of the hub 5, adopts its own
mode and its own amplitude of expansion, depending on the
temperature at which it finds itself, so that over the
support span as a whole, said expansion is distinct from
the theoretical ideal expansion as a function of which the
conical thrust surfaces 12, 13 are dimensioned and pointed
by construction.
In practice, this creates, at least temporarily, a
phenomenon equivalent to the above-mentioned phenomenon of
"defocusing", causing, depending on the situation, under-
compensation or over-compensation as described above.
In order to compensate for these phenomena, and thus in
order to improve the dynamic thermal behavior of the
device, in particular during optionally periodic rapid
transient phases, during which the thermal environment of
the device is modified over a period shorter than its
response time as regards assimilation or dissipation of
heat energy, the inventors have made provision, in
accordance with a characteristic that can constitute a
separate invention, independently from the arrangement of
the thrust members, and in particular from their conical
tapering, for the first or the second thrust member 10, 11
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to be axially backed up, against the wheel 2, by an
elastically deformable compensation system 25 that is
interposed between the thrust member in question and an
abutment member 26 fastened to the shaft 3.
By way of example, the abutment member 26 may be formed
by a nut, of the type having notches, that may
advantageously be prevented from moving in rotation by
means of one or more clips 26' that radially connect a
notch formed in said nut to a corresponding indent provided
in the shaft 3.
Advantageously, the compensation system 25 acts as a
spring having stiffness that is determined such that said
spring can deform, either by compressing by contraction in
order to absorb over-stress caused by the interference of
the wheel 2 against the thrust member 10, 11, or,
conversely, by expanding to hold the thrust member 10, 11
pressed and compressed against the seat 14, 15 of the hub 5
in the event that thermal expansion tends to cause relaxing
or indeed separating of the surfaces.
Thus, it is possible continuously, and in fine and
reactive manner, to accommodate any defocusing resulting
from a thermal gradient within the same part and causing
non-uniform expansion that no longer coincides with the
ideal slopes defined by the thrust member, while also
maintaining a clamping force that is sufficient to hold the
wheel 2, in particular radially, but that is sufficiently
moderate to avoid plastic deformation, premature wear, and,
more generally, degradation of the parts and of the device
1.
Thus, the assembly proposed tolerates and indeed
corrects dimensional variations that are non-uniform and/or
of large amplitude of the wheel and of the shaft.
Advantageously, as shown in the figures, the
compensation system 25 can form a sort of "breechblock"
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29
that comes to bear against the face of the thrust member
10, 11 that faces away from the thrust surface 12, 13 that
said thrust member presents to the wheel 2, the degree of
nominal compression being determined as a function of the
adjustment of the abutment 26, and more particularly of the
tightening torque of the corresponding nut.
To this end, the clamping nut, and more generally, the
thrust members, may be engaged over the shaft 3 by means of
an anti-recoil threaded portion, of the "interrupted
thread" type having its thrust surfaces particularly steep,
or indeed substantially radial.
Preferably, the compensation system 25 includes at
least a first axially deformable member 27 and a second
axially deformable member 28, of the resilient washers or
rings type, which washers or rings are stacked and
compressed axially.
In particularly advantageous manner, the first
deformable member may have a stiffness less than the
stiffness of the second deformable member 28.
In other words, it is advantageously possible to create
a sort of stack comprising a "soft" washer having
relatively low stiffness but a good elastic deformation
amplitude, and at least one, and preferably two "hard"
washers 28, 29 of stiffness and/or of thickness greater
than the stiffness and/or thickness of the "soft" washer,
but of smaller maximum amplitude of movement.
It is thus possible to create progressive differential
compensation, the "hard" washers making it possible, so
long as the axial dimension variation between the parts
does not exceed a certain threshold, to maintain a
compression load that is relatively high, the "soft" washer
supplying, if necessary, i.e. when said axial dimensional
variation exceeds a usual threshold exceeding the capacity
of the "hard" washers, a stroke that is sufficient to
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maintain the assembly as a whole under axial stress,
thereby avoiding relaxation that is too great and/or too
sudden in the clamping, even though the residual holding
stress is more moderate than the nominal holding stress.
5 Naturally, the thrust member 10, 11 in question is
advantageously mounted to move in axial translation
relative to the shaft 3, so that, in particular, it can
move when stresses are exerted on one side by the
dimensional variation of the hub 5 relative to the shaft 3,
10 and on the other side by the compensation system 25.
Thus, more generally, the device preferably includes,
on either side of the wheel 2, firstly a thrust member (the
second thrust member 11 in this example) fastened to the
shaft (at least axially, in the clamping direction), or
15 indeed incorporated into said shaft, said (second) thrust
member procuring rigid and fixed thrust for said wheel, and
secondly a thrust member (the first thrust member 10, in
this example) urged against the other thrust member and
mounted to move under a resilient force (in the clamping
20 axial direction in this example).
In addition, the above-described compensation system 25
may naturally be advantageously adapted to fastening any
type of part (wheel, e.g. bladed or toothed wheel, pulley,
hinge flap, etc.) to a pin or to a shaft.
25 Preferably, the first thrust member 10 is formed by a
frustoconical thrust ring 30, as shown in particular in
Figures 1, 3, and 13, which ring is distinct from the wheel
2 and from the shaft 3.
Advantageously, this ring can come to form a wedge-
30 shaped thrust, preferably directly against the shaft 3 and
against the first seat 14 provided in the hub of the wheel
5.
Preferably, the frustoconical ring 30 is angularly
split up into at least two independent blocks 30A, 30B, and
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31
preferably into three independent blocks 30A, 30B, 30C,
each of which preferably covers an angular sector that is
substantially equal about the shaft 3.
The frustoconical ring 30 can thus be reconstructed by
a succession of jaws, or its blocks can be totally
separated, or optionally interconnected by flexible links,
and, for example, distributed over about 120 each, thereby
making it possible for each block to move, if necessary,
relative to the adjacent blocks, and, in particular to move
away or towards said blocks, so that the ring 30 can freely
accommodate the variations in perimeter caused by the
expansion and contraction of the shaft.
In addition, said frustoconical ring 30 may have hinge
slots 31 that are radially non-through slots, but that
subdivide the ring, and more particularly the blocks 30A,
30B, 30C, e.g. with at least two slots per block, so as to
make them easier to bend when it is necessary to
accommodate a change of radius of curvature of the shaft 3.
Advantageously, such hinge slots 31 may correspond to
saw cuts that that crenellate the outside periphery of the
ring 30, so that each block is formed of a chain of
segments that are hinged together via their weakened link
zones.
The ring 30 that is thus made more flexible can then
continuously match the shape of the outside surface of the
shaft 3 against which surface it comes to bear.
Preferably, the compensation systems 25 and the
frustoconical ring 30 are secured together by tongue-and-
groove machining that avoids improper positioning of or
radial leakage from the blocks 30A, 303, 30C.
Preferably, such securing takes place at a level close
to the mean diameter of the first conical thrust surface 12
or a little beyond that, in the upper half, i.e. in the
radially outermost half, of the back of the frustoconical
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32
ring 30, so that the axial stress exerted by the
compensation system 25 tends to press the sole of said ring
30 against the shaft 3 rather than separating it therefrom
by tilting, thereby reinforcing the assembly.
In addition, as shown in Figure 4, it is remarkable
that the abutment member 26 can procure substantially
conical thrust for the compensation system 25, which thrust
follows a third generator cone C26 having its vertex F26
situated substantially in register with the junction where
the compensation system 25 meets the thrust member 10 that
it backs up.
Advantageously, such a provision makes it possible, in
a manner analogous to the manner described above for the
junction between the wheel and the thrust members, to
compensate, if necessary, for the phenomena of expansion
affecting the axial portion of the shaft that lies in the
zone capped by the "breechblock" formed by the compensation
system 25. The entire axially captive (and stressed)
portion of the shaft, lying firstly between the thrust
members 10, 11, and then beyond that, to the abutment
member 26, is thus compensated for expansion, by means of a
plurality of successive conical thrusts each covering a
respective segment.
In accordance with a characteristic that can constitute
a separate invention, in particular independently from the
arrangement and from the conical tapers of the thrust
members 10, 11, the first thrust member 10 and the second
thrust member 11 can be designed to maintain the inside
surface of the hub 5 of the wheel 2, i.e. the wall of its
bore 6, away from the outside surface of the shaft 3 that
faces it, and to do so over at least 50%, and preferably at
least 75%, or indeed all of the support span lying between
said thrust members 10, 11.
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33
In other words, the thrust members 10, 11 may also
optionally act as spacers making it possible to provide, at
least initially, and preferably substantially to maintain
radial clearance between the shaft 3 and the hub 5.
Advantageously, such operating clearance J, shown in
particular in Figures 3 to 7, makes it possible to absorb,
if necessary, the differential radial expansion between the
shaft 3 and the hub 5, while avoiding any effect of
clamping of the shaft 3 by said hub 5 that could cause
plastic deformation, or indeed cracking or splitting of the
hub.
Preferably, this clearance is in the form of a
cylindrical chamber that extends over the entire support
span d3 of the shaft 3 that is defined between the thrust
members.
Advantageously, such a provision also improves the
self-centering procured by the conical thrust surfaces and
makes it possible to stress the hub 5 essentially in axial
compression so as to ensure it is held stationary, no
intermediate portion of the shaft coming to bear against,
deflect, or hinder the positioning of the hub.
Preferably, the radial clearance J lies substantially
in the range 1 millimeters (mm) to 4 mm and/or represents
about 0.5% to 2% of the radius of the shaft 3.
Preferably, it is calculated, where appropriate, so
that it can change, and in particular, decrease, so as to
reach, under steady-state operating conditions, a
predetermined level of clearance that is preferably less
than the initial value of said clearance on assembly, or
indeed a predetermined level of operating tightness of fit
making it possible to reinforce the securing between the
shaft and the wheel. If it is desired to obtain such an
effect when the temperature might rise while operation is
starting, the coefficient of thermal expansion of the shaft
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34
3 is chosen to be greater than the coefficient of thermal
expansion of the wheel 2.
In addition, in accordance with a characteristic that
can constitute a separate invention, the coupling means 40
may have at least one transverse element 40', of the key
type, that connects the first thrust member 10 to the wheel
2 at the first conical thrust surface 12, or, in
particularly preferable manner, connects the second thrust
member 11 to the wheel 2 at the second conical thrust
surface 13, the thrust member 10, 11 in question being
itself prevented from moving in rotation on the shaft 3, or
indeed formed integrally therewith, so that any movement in
rotation of the wheel 2 relative to said thrust member 10,
11 and thus relative to said shaft 3 is prevented.
Advantageously, such a provision makes it possible to
reinforce the fastening of the wheel and to transmit torque
that is particularly high between the shaft and said wheel
or vice versa.
It is remarkable that this solution makes it possible
to distribute the torque transmission over a plurality of
transverse elements, by limiting the concentrations of
stresses, and by coming into engagement on a relatively
large and solid and thus particularly strong conical
surface of the hub, unlike usual solutions that make the
hub weaker over its entire length by providing it with
grooves or with fluting.
In addition, the radial extension component of the
transverse elements that are projecting and inclined
relative to the axis advantageously increases the working
lever arm relative to the surface of the shaft (and
relative to the axis).
Furthermore, this end coupling advantageously makes
assembly easy by it being by mere interfitting engagement,
guided by the shaft itself.
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Preferably, as is shown in Figures 1 to 13, the
transverse coupling element 40' is formed by a key, e.g. a
substantially rectangular block shaped key, a portion of
which is designed to be received in a groove 41 provided in
5 the conical surface of the thrust member 10, 11 in
question, and the other portion of which is designed to
emerge from said groove 41 and to engage in a stop recess
42 that is substantially complementary, and that is
provided in the corresponding portion of the wheel 2, said
10 key being secured to the thrust member 10, 11, or indeed,
respectively, to the wheel 5, e.g. by screw-fastening, in
particular in order to avoid it tilting during removal of
the wheel.
Fastening the key 40' to the end wall of the cavity of
15 the groove 41 or of the stop recess 42 avoids causing said
key to be raised and jammed by chocking, shown in
Figure 14, which might otherwise prevent the thrust member
10, 11 and the seat 15 from coming apart when it is desired
to remove the wheel 2.
20 In general, it is remarkable that the construction
provisions of the invention advantageously make it possible
to procure a reversible assembly whereby each element, and
in particular the wheel 2 and the first thrust member 10 or
the compensation system 25 can be removed and replaced or
25 fitted back in place.
In another variant embodiment, shown in Figure 15, the
device may include a third thrust member 50 situated on the
same side of the wheel 2 as the first thrust member 10, set
back axially therefrom, and having, against the wheel 2, a
30 substantially conical third thrust surface 52, situated at
a diameter greater than the diameter of the first thrust
surface 12, and focused on the first focus F12.
In particularly preferential manner, the device may
also include a fourth thrust member 51 having a
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substantially conical fourth thrust surface 53 situated set
back from the second thrust member at a diameter greater
than the diameter thereof.
It is thus possible to obtain a structure having two
stepped bi-conically tapering rings having all of their
conical thrust surfaces converging towards the same focus,
so as to form two pairs of thrust surfaces disposed in an
X-shape, each pair being stepped axially relative to the
other, and being suitable for withstanding the differential
expansion of the parts.
In general, the configuration and the dimensioning of
the various elements is performed with reference to initial
assembly performed at ambient temperature.
However, it is possible to provide nominal
dimensioning, and in particular an arrangement of the
conical thrust surfaces having its ideal configuration
corresponding to the configuration of the assembly once it
is brought to its operating temperature.
It is remarkable that the device, and in particular the
materials and the various component parts of the device,
may advantageously be designed to withstand, without being
damaged, durable exposure to a fluid, and more particularly
to a gas, that is at a temperature that is relatively high,
and in particular greater than or equal to 100 C, 200 C,
500 C, 700 C, or indeed 1000 C.
The device is particularly suitable for "high-
temperature" applications and may, in particular, by way of
non-limiting example, be designed for extracting exhaust
gases from combustion or incineration, or gases formed
above molten baths in the mining or metallurgy industries,
for generating electricity from a stream of gas or of
stream discharged by a furnace or by a boiler, or indeed
for extracting or mixing hot reagents in the chemicals
industry.
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It is also suited to any use in which it is exposed to
durable temperature gradients, in particular between the
wheel and the shaft, or between the upstream portion and
the downstream portion of the assembly relative to the
direction of flow of the fluid, or indeed to optionally
rapid temperature variations over time, the amplitude of
which is of the order of larger than 100 C, 200 C, 500 C,
700 C, or even 1000 C.
Naturally, the present invention also relates to a
method of assembling a wheel 2 onto a shaft 3.
Advantageously, said method includes a clamping step
(a) during which the wheel 2 is held stationary on the
shaft 3 by clamping said wheel between firstly a first
thrust member 10 and secondly a second thrust member 11
that are urged axially one against the other, the first
thrust member having, against the wheel 2, a substantially
conical first thrust surface 12 that is substantially
carried by a first generator cone 012 having its vertex F12
or "first focus" pointing towards the second thrust member
11, and having the half-angle at its vertex oc12 greater than
or equal to the angle of adhesion T12/2 corresponding to the
coefficient of friction between the first thrust surface 12
and the wheel 2.
Preferably, prior to said step (a), said method
includes a pre-positioning step (b) during which the wheel
2 is engaged over the shaft 3, the shaft being free to move
in rotation so long as the clamping has not been performed.
Advantageously, the wheel can slide along the shaft until
it comes into abutment against the second thrust member,
the stop recesses 42 coming to fit over the coupling keys
40' that thus penetrate into engagement in the hub 5.
During another stage of this pre-positioning step (b),
the wheel 2 and the conical ring 30 are then fitted over
the shaft in succession, where applicable the ring being
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reconstructed by pre-assembling the blocks 30A, 30B, 30C
over the circular groove of the washer 29 of the
compensation system 25, and then said conical ring 30 is
moved partially in translation until it comes into thrust
abutment against the seat 14 of the hub 5.
It is then possible to perform the clamping
progressively by engaging the abutment member 26 with the
thread on the shaft 3, and then by tightening it so as to
force the ring 30 into the hub 5, until a predetermined
tightening torque is reached that corresponds to the
desired intensity of the clamping force in axial
compression.
In doing this, the compensation system 25 is pre-
stressed axially in compression, and said system is
compressed, thereby advantageously accumulating a stroke
reserve that, if necessary, enables it to redeploy
subsequently so as to compensate for any separation of the
wheel relative to the thrust members, but while also
preserving a margin of contraction compatible with the
maximum compression stresses acceptable by the hub, or
respectively with the maximum traction stresses acceptable
by the shaft 3.
Generally, and independently of whether or not a
compensation system 25 is present, the shaft 3 can thus
advantageously be used as a tie, stressed in traction, that
connects, directly or indirectly, the first thrust member
10 to the second thrust member 11, by co-operating via
specific and distinct securing with each of said thrust
members 10 and 11, in order to stress said thrust members
in mutual compression towards each other.
To this end, although said shaft may preferably
constitute the only member withstanding all of the traction
load necessary for clamping the wheel between said thrust
members, it is not impossible for consideration be given to
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putting in place other peripheral ties connecting the first
thrust member 10 to the second thrust member 11, e.g. of
the nut-and-bolt type, so that said shaft withstands only a
fraction, preferably a majority fraction, of the traction
force resulting from the axial clamping.
Advantageously, by forcing the two thrust members to
move closer together, and more particularly by forcing the
first and second conical thrust surfaces 12, 13 to move
closer together, firstly the wheel is caused to be centered
relative to the shaft, and secondly the bore 6 is caused to
settle some distance from the wall of the shaft 3, it being
advantageously possible for the clamping force to be
exerted significantly and preferably to a majority extent
along an axial component.
It is remarkable that the pre-positioning step (b) and
the clamping step (a) may preferably be implemented while
the shaft 3 is placed substantially vertically, in order to
facilitate engaging and centering the wheel 2 on the shaft,
and more particularly on the second conical thrust member
11, in particular under the effect of gravity, without
having to compensate for any off-centering of the wheel 2
relative to the shaft 3, i.e. any non-uniform distribution
of the operating clearance J between the hub 5 and the
shaft 3, that would be caused by the weight of the wheel 2
if the mounting was performed while the shaft was placed
horizontally.
In addition, the method of assembly is advantageously
reversible, insofar as it limits or indeed prevents any
direct adhesion contact between the shaft 3 and the wheel
2, the forces being borne via at least one removable thrust
member 10, in which the contact surfaces coming into
contact with the shaft and with the wheel are relatively
small, and which can, by means of the conical taper that
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facilitates extracting it, be easily separated not only
from the shaft 3 but also from the hub 5.
Advantageously, the invention thus makes it possible to
procure a rigid assembly that is particularly stable and
5 safe, suitable both for withstanding transverse imbalance
and also for transmitting high torque, it being possible,
in addition, for said assembly to be adapted to driving
elements of large dimensions, that are heavy, and that have
high inertia, all this with an axial clamping force that is
10 particularly moderate.
In spite of these performance values, said assembly
further remains reversible, needs only a small number of
fastening elements, and is of relatively simple design,
compact, or indeed lightweight compared with the scale of
15 implementation.
It makes it possible, in addition, to accommodate the
dimensional variations of the parts, regardless of whether
they are relative variations between parts or non-uniform
deformations in the same part, and regardless of whether
20 such variations result from thermal expansion or indeed hot
centrifugal creep under the effect of the speed of
rotation, and it does all this while maintaining
appropriate, or indeed substantially constant clamping
stress.
25 Advantageously, the type of assembly proposed further
makes it possible to consider functionally associating
materials having grades and properties that are very
distinct, for forming the wheel and the shaft, and makes it
possible, where applicable, to omit refractory super-alloys
30 that are particularly costly and difficult to work for
manufacturing the shaft.
By means of the invention, it is possible, in
particular to procure fans of large dimensions, e.g.
driving wheels of diameter of approximately in the range
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0.5 meters (m) to 2 m or 3 m and of weight of approximately
in the range 100 kilograms (kg) to over 1 metric tonne (t),
or indeed 3 t, while exerting an initial axial clamping
force of approximately in the range 5000 decanewtons (daN)
to 50,000 daN, said fans optionally being capable of
working under extremely severe thermal conditions, without
causing premature wear or fatigue in the parts, which, in
any event, can be removed and replaced separately, without
damaging the remaining parts.
SUSCEPTIBILITY OF INDUSTRIAL APPLICATION
The invention is industrially applicable to designing,
manufacturing, and using industrial fans.
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