Note: Descriptions are shown in the official language in which they were submitted.
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Pantograph with a damped head suspension"
The present invention relates to a pantograph
intended for the collection of the current for railroad
railcars from catenary-suspension overhead lines.
S The subject of the invention is more particularly
a pantograph in which the regularity of the contact of
its head with the catenary line is improved, in parti-
cular when the train i8 running at high speeds.
It is known to construct pantographs, in which
the upper arm supports a head which ensures the contact
with the line, this head being connected to the upper arm
by an elastic suspension, for example having helical
springs.
These pantographs are usually also provided with
a suspension which acts on the whole structure of the
pantograph. In some cases, this latter suspension com-
prises a damper which is situated at the lower part of
the pantograph.
The Applicant has analyzed in detail the behavior
of such a pantograph when collecting current at high
speed. This analysis concerns, in particular, the contact
force F between the catenary line and the friction strips
of the pantograph, as illustrated in Figures 1 and 2.
Thus, Figure 1 shows diagrammatically a
pantograph 1 moving at the speed v beneath a catenary-
suspension current line 2. This suspension is effected by
way of droppers 3 which ensure that the line 2 extends in
a direction parallel to the track, beneath the spans 4.
Figure 2 is a graph of the variations in the
contact force F as a function of the distance d traveled
under the operating conditions of Figure 1.
By analyzing these curves, the Applicant has been
able to establish:
- that the contact force F has two characteristic
periodicities: Ll corresponding to the interval between
two successive spans 4, and L2 corresponding to the
interval between two successive droppers 3;
- that the most abrupt variations in this contact
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force F are generated on the scale of the intervals L2
between the droppers 3;
- that the known pantographs respond to the
llhighll frequency f2 = v/L2 with their head suspens~on;
- that these pantographs respond to the "low"
frequency f1 = v/L, with their suspension which acts on
the whole of their structure.
Typically, if the spans 4 ~re spaced apart by
60 m, and if this interval corresponds each time to ten
droppers 3 spaced apart by 6 m, the pantograph will be
sub~ected, for a speed v = 250 km/h, to a force having
the two preferred frequencies
f, = l.16 Hz
and
f2 = ll.6 Hz
Given that railroad traffic i5 traveling at
increasingly high speeds, it is important to construct
pantographs which have a ~atisfactory behavior in
response to high-frequency stre~ses of the order of this
value of ll.6 Hz, or even greater than this.
Now, the known pantographs do not meet this
requirement since the oscillations of the head in
response to this high frequency are not damped, with the
result that the contact force F has substantial varia-
tions between a minimum value Fmln and a maximum value Fm~.The difference between these minimum and maximum values
must be reduced. Indeed, a low value for Fmin means that
there is a likelihood of the friction strips being
separated from the catenary line. These separations are
detrimental to the quality of the current collection by
introducing dis~unctions, and cause electric arcs which
damage the friction strips and the catenary line. More-
over, a high value for Fm~ gives rise to points of
excessive stress between the friction strips and the
catenary line, which are also a cause of premature wear
of these members.
The ob~ect of the present invention is to
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overcome the above problems caused by the droppers of the
catenary suspension by creating a pantograph which makes
it possible, in particular, to improve the collection of
the current at high speed and to reduce the wear of its
friction strips and that of the catenary line.
The invention thus propose~ a pantograph for a
railroad vehicle, in particular a high-speed railroad
vehicle, comprising an upper arm, the end of which sup-
ports a head for collecting the current from a catenary
line suspended via droppers spaced apart along the whole
length of said line.
According to the invention, this pantograph is
defined in that the head is connected to the end of the
upper arm via elastic suspension means comprising a
damper adapted in order to act on the high force fre-
quencies to which the pantcgraph is subjected, in par-
ticular on the frequencies when it passes the droppers of
the catenary su~pension of the line.
This damper makes it possible to diminish sub-
stantially the most abrupt variations in the contact
force which are generated on the scale of the interval
between the droppers of the catenary suspension. The
practical result of this i~ an elimination of the separa-
tions and of the excessive stresses between the head and
the line.
According to a preferred version of the inven-
tion, the damper has damping properties which are suf-
ficient to diminish the variations in the contact forces
due to the droppers, and to maintain these variations
between a minimum value which iB sufficiently far from
zero to prevent the head from being separated with
respect to the line, and a maximum value situated below
that generating an excessive friction between the head
and the line.
Other features of the invention will emerge from
the following description which is to be read in con~unc-
tion with the attached non-limiting drawings, in which:
- Figure 1 is a diagrammatic view in elevation of
a pantograph moving beneath a catenary-suspension current
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line,
- Figure 2 is a graph of the variation~ in the
contact force between the current line and the friction
strips as a function of the distance traveled by the
pantograph,
- Figure 3 is a perspective view of a pantograph
according to the invention in the extended po6ition,
- Figure 4 shows a ~uspension element intended
for the pantograph. according to the invention.
A pantograph can be seen in Figure 3, the base 10
of which is fixed onto the railroad vehicle (not shown)
by brackets 11. A control and balancing device 12 makes
it possible to extend or collapse the pantograph, as well
as to provide a static force on the catenary wire. This
device 12 acts on a ~oint 13 in order to pivot a lower
arm 14 connected to an upper arm 15 via another ~oint 16.
The stability of the structure is obtained by two addi-
tional rods 17, 18.
The head 20 of the pantograph comprises a bow 21
which supports two friction strips 22 substantially
perpendicular to the catenary line (not shown). This head
20 i8 connected to the end of the upper arm 15 via two
damped-suspension casings 25 situated symmetrically with
respect to the catenary line. These damped-suspension
casings 25 can, for example, bring into play the elas-
ticity of a spring, and a hydraulic damper.
A particular example is shown in Figure 4 where
a damped-suspension casing 25 can be seen which comprise~
a pin 30 traversing a cylindrical housing 31 integrally
connected to the end of the upper arm 15. The pin 30 is
prov~ded at its upper end with fixing means 32 intended
to receive the bow 21. The pin 30 comprises, perpen-
dicular to $ts direction, a piston 33 in the form of a
disk centered on the pin 30 and the diameter of which is
slightly less than that of the housing 31. This piston 33
can slide, together with the pin 30, along the housing
31. Annulnr ~eals 34, 35 ensure the passage of the pin 30
in a sealing manner, and an annular seal 36 permits a
sealing contact between the periphery of the piston 33
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and the side walls of the housing 31. A helical spring 37
is in.serted between the bottom 31a of the housing 31 and
the lower face of the piston 33. Furthermore, the housing
31 contains a viscous fluid 39 which can pass through the
piston 33 via orifices of small ~ection 38 calibrated in
order to provide the desired damping.
According to an advantageous version of the
invention, the pantograph furthexmore comprises a lower
damped suspension 40 which responds to the movements of
the whole pantograph. This lower damped suspension can
act on the joint pin 13 of the lower arm 14, or on the
lower arm 14 itself.
When the pantograph 1 is moving at the speed v
beneath a catenary line, as depicted in Figure l, it is
subjected to contact stresses which come, on the one
hand, from the control device 12 which applies the head
20 of the pantograph against the line 2 and, on the other
hand, from the catenary line 2 itself. This catenary line
has a modulation at regular intervals which is caused by
the method of suspension. The interval L1 between the
spans 4 introduces fluctuations in the contact force of
"lowl~ frequency f1 = v/L1, typically of the order of
magnitude of 1 Hz for a speed v greater than 200 km~h.
The interval L2 between the suspension droppers 3 in-
troduces fluctuations in the contact force of ~high~ fre-
quency fz = v/L2, typically of the order of magnitude of
10 Hz for a speed v greater than 200 km/h.
The fluctuations in frequency fl are absorbed and
damped by the lower damped suspension 40, but the inertia
of the whole pantograph on which this lower damped
suspension 40 acts is too great for this lower suspension
to be able to respond sufficiently quickly to the
stresses of higher frequency f2.
This response to the frequency f2 resulting from
the droppers 3 will be made by the head suspension 25
which involves a smaller dynamic mass. As this head sus-
pension 25 is damped, the variations in the contact force
on the scale of the interval L2 will be diminished. Now,
as was seen in the preamble to the present description,
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it i8 on this scale L2 that the most abrupt ~ariations in
thi~ contact force are a priori generated. The invention
therefore make~ it possible to reduce these variations
substantially such that the extreme values F~n and Fm~ of
the contact force come nearer to each other. The increase
in F~n all but eliminates the risks of separation, and
the reduction in Fm~ per~its a collection which does not
wear down the friction strips on the catenary line
excessively. Thus, FmlD is suf~iciently far from zero in
order to prevent the head 20 from being separated with
respect to the line 2, and F~ doeR not exceed the value
which generates an excessive friction between the head 20
and the line 2.
Maximum velocities of the order of 0.5 m/s are
typically found in the relative movements in the head
suspensions. It i8 generally de~ired to provide viscous
damping forces of the order 100 N. A typical value for
the viscous damping constant f of the damped suspension
i8 therefore 200 N s/m. If the overall stiffness of the
springs of this head suspension has a value k = 9000 NJm,
and if the head of the pantograph weighs m = 10 kg, then,
under these conditions, a typical value will be obtained
for the reduced damping coefficient z of: z = f/2 ~ =
0.33.
In a more general manner, a value for this
coefficient z lies between the values 0.2 and 0.4 will
provide, in the case of high-speed trains, an advanta-
geous compromise between the damping of the head suspen-
sion 25 and its response time.
It will also be possible, in practice, for the
optimum characteristics of the damper to be determined
experimentally during tests. Indeed, during these tests
it will be possible to compare the re~ults obtained from
a series of dampers having different characteristics, and
thus to retain that damper or dampers enabling the
difference between the forces generated by the frequen-
cies due to the droppers 3 to be reduced efficiently.
The invention is not limited to the example
described above. Many modifications may be made to it
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without going beyond the scope of the invention. Thus, a
pantograph head has been described consisting of a bow
which comprises two blades supporting the friction
strips. In fact, the invention applies to any type of
pantograph head which can be provided with a suspension
such as, for example, pantographs with independent
suspension strips.
The damper or dampers of the head suspension of
the pantograph can, of course, be separated from the
suspension springs, the essential condition being that
this damper or these dampers are as near as possible to
the head of the pantograph.
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