Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
03~892
~Pantograph with two coupled heads for
railroad motorcars~
The present invention relates to a pantograph
intended for collecting current for railroad motorcars
from overhead contact lines. It concerns a pantograph in
which the regularity of the contact with the overhead
contact line is improved by virtually elLminating
dewiring.
To reduce the probability of dewiring between the
pantograph and the overhead contact line, i~ is known to
construct ~o-called "independent-strip" pantographs
comprising an upper arm, the end of which ha~ a support
on which two collecting heads are mounted. In this type
of pantograph, each head is mounted on said support via
its own suspension employing, for example, a helical
spring. These suspensions are independent.
With these pantographs of the prior art, the
probability of dewiring i~ reduced since the probability
of the two independently suspended heads simultaneously
coming away from the overhead contact line is lower than
the probability of an individual head coming away.
- However, it should be noted that the causes of
this dewiring are not independent. The main cause comes
from the irregularities which may be encountered along
the current line, in particular from the overhead contact
system droppers for this line, which suspend it from a
messenger fixed to pylons placed along the track. When
the pantograph passes one of these irregularities, the
two heads are affected almost simultaneously by an
impulse which tends to disconnect them from the line. As
the suspensions are independent, the two heads may come
away simultaneously from the line if this impulse is
sufficient. Such a complete dewiring of the pantograph
results in a momentary dis~unction of the electrical
installations of the motorcar and in the appearance of
an intense electric arc, which damages both the heads of
the pantograph and the overhead contact line if it occurs
too often.
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The object of the invention is to virtually
remove the probability of this dewiring.
Thus, the sub~ect of the invention iB a pan-
tograph for railroad motorcars comprising an upper arm,
the end of which has a support to which two heads in-
tended to make the connection to an overhead current line
are connected.
According to the invention, this pantograph is
distinguished in that ~he heads are mounted independently
of one another on the support by connection means which
guide them in their movement transversely to the current
line and in that suspension means are mounted on the
connection means so that, when one of the heads moves
relative to the support, a force having an opposite
direction is exerted on the other head.
By virtue of this device, if one of the heads
tends to come away from the line a force is applied to
the other head, the effect of which is to hold it against
the line. The complete dewiring of the pantograph is
therefore virtually eliminated.
According to a preferred version of the inven-
tion, the suspension mean~ comprise an elastic member.
Advantageously, this suspension is damped by a damper
provided in these same suspension means.
In an advantageous embodiment, each of the heads
is linked to the support by at least one connecting
~tructure having the form of an articulated parallelo-
gram, one side of which forms part of the support, with
its opposite side fastened to said head, and the other
side~ of which consist of at least two parallel connect-
ing rods of the same length, articulated at one end on
said support and at the other end on said head. These
connecting structures in the form of a parallelogram,
corresponding respectively to the two heads, can be
placed opposite one another on either side of the sup-
port. The connecting structures thus paired are then
linked in twos by a linking member fixed, at each end, to
one of the articulated connecting rods forming sides of
the corresponding connecting structure in the form of a
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parallelogram~
This configuration permits effective guidance of
the heads transversely to the overhead contact line in
accordance with a perpendicular to the plane of the track
and the obtaining of the desired dynamic effect. The
above linking member can incorporate the suspension and
damping devices.
Other features and advantages of this invention
will become apparent in the description below. In the
attached drawings, given by way of non-limi~ing example:
- Figure 1 is a ~iew in elevation of the upper
part of a pantograph according to the invention in
accordance with the plane I-I of Figure 2, and
- Figure 2 is a plan view of this pantograph.
Mounted on the upper arm S of the pantograph are
two support~ 22 intended to support the collecting heads
20. Each support 22 i8 articulated on the arm 5 and, in
a known manner, a stabilizing bar 4 is provided to keep
the support 22 in a stable position with respect to the
overhead contact line L (shown in dotted lines in the
figures).
This pantograph comprises two heads 20, in which
a bow 18 supports one or more wearing strips 19 which
extend substantially perpendicularly to the overhead
con~act line L and in a plane parallel to the track. The
two heads are connected to the supports 22 by connection
means which guide them in the direction of the line L.
Thus, each head 20 has two stems 25 which extend
perpendicularly to the directions defined by the wearing
strips 19 and by the overhead contact line L. On each of
these stems 25 are articulated two parallel connecting
rods 23, 24 of the same length, the articulation pins
23a, 24a being situated on the stem 25 at a distance h.
These two connecting rods 23, 24 are articulated at their
opposite ends on one of the supports 22, the correspond-
ing articulation pin~ 23b, 24b being separated, on this
support 22, by the same distance h. The means for con-
necting the heads 20 to the support 22 therefore comprise
two pairs of connecting structures in the form of an
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articulated parallelogram, one fixed side of which, of
length h, forms part of a support 22, the side opposite
this fixed side of which forms part of a stem 251 and the
other two opposite sides of which consist of two articu-
lated connecting rods ~23, 24).
The articulation pins 23a, 23b, 24a, 24b at the
vertices of these parallelograms are all parallel to the
direction of the wearing strips 19, so that the heads 20
are subject to displacement, with respect to the support
22, according to a translational movement transversely to
the overhead contact line L, perpendicular to the plane
of the track.
For each of these connecting structures in the
form of a parallelogram, the upper connecting rod 24 has
a pro~ection 28 transversely to its axis.
The~e connection means (structures in the form of
a parallelogram, and projections 28) as a whole have a
positional symmetry with re~pect to a plane P which
passes through the centre of the support 22 and which is
perpendicular to the direction of the overhead contact
line L and therefore to the plane of the track.
The connecting-rod projections 28, which are
paired, that is to ~ay situated opposite one another with
respect to this plane P, are linked by a linking member
30.
The linking member 30 is, in the example il-
lustrated, articulated at its ends on the corresponding
ends of the connecting-rod pro~ections 28.
Advantageously, the linking member 30 has a
helical spring 42 and a hydraulic damper 37a, 37b, in
which a piston 37b connected to one of the connecting-rod
pro~ections 28 can slide in a cylinder 37a which contains
a hydraulic fluid and which is connected to the paired
connecting-rod pro~ection 28. In this configuration, the
helical spring 42 bears at both ends on shoulders 38a,
38b, present on the cylinder 37a and on the end of the
piston pin 37b respectively.
With this pantograph, if one of the heads 20
tends to come away from the overhead contact line, that
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is to say if it i5 given, with respect to the support 22,
an impulse in the direction of the motorcar, then a force
in the opposite direction i8 communicated to the other
head 20 via the connecting structures in the form of a
parallelogram, and the linking members 30: the connecting
rods 23, 24 pivot about the pins 23a, 23b, 24a, 24b and
the displacement of the projection 28 is transmitted to
the paired projection 28 by the linking member 30,
resulting in a force which holds the second head 20
against the overhead contact line L. Since the linking
member 30 employs a spring 42, it also provides the
elastic suspension of the heads 20, which permits the
upper part of the pantograph to respond to the variations
in the contact force between the wearing strips 19 and
the overhead contact line L. In addition, hydraulic
damping permits attenuation of the variations in this
contact force by reducing the amplitude of the movement
of the heads 20.
The dewiring between the wearing strips 19 and
the line L is virtually eliminated and, by this same
assembly, the regularity of the contact force is
improved.
It should be noted that the damped suspensions of
the pantograph in the region of its head usually require
the use of a damper having a relatively low damping
coefficient with the constraint of a minimal space
requirement to avoid disadvantageously affecting the mass
and the aerodynamics of the device. This type of damper
generally involves solid friction which is quite con-
3iderable given the viscous damping obtained and, sincethis solid friction is not well controlled, the response
of the damped suspension will not be controlled satis-
factorily. By virtue of the assembly proposed by the
present invention, it is possible to produce thi~ damped
suspension with a higher viscous damping coefficient so
that the solid friction is no longer a problem. In fact,
the head-connecting structures in the form of a
parallelogram, and the connecting-rod projections 28
produce, during the pivoting of these structures, a
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reduction in amplitude between the movement of the heads
20 transversely to the line L and the movement trans-
mitted to the linking member 30. It is thu~ possible to
obtain greater damping between the piston 37b and the
cylinder 37a while delivering the same effective damping
in the region of the heads 20. The reliability of the
damped ~uspension i8 therefore improved.
Of course, the invention i~ not limited to the
specific example described above. Numerous geometrical
variants thereof are possible without departing from the
scope of the invention.
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