Note: Descriptions are shown in the official language in which they were submitted.
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Compressor system for a rail vehicle and method for operating the compressor
sys-
tem with safe emergency operation
FIELD OF THE INVENTION
The invention relates to a compressor system for a rail vehicle, comprising a
compressor
which is driven by an electric machine via a drive shaft and which serves for
generating
compressed air for at least one compressed-air vessel, wherein the electric
machine can
be controlled at least indirectly by means of a regulation device for
operation of the elec-
tric machine at at least a rated rotational speed between a maximum rotational
speed and
a minimum rotational speed, wherein furthermore, in a compressed air-
conducting line
arranged downstream of the compressor, there is arranged at least one pressure
sensor
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for determining the pressure for the regulation device. The invention also
relates to a
method for controlling the compressor system according to the invention.
BACKGROUND TO THE INVENTION
Compressors in rail vehicles are subject to a variety of, in part, conflicting
demands,
such as for example a high delivery output, adequate activation duration, low
sound
emissions, low energy consumption, a small structural space, and low purchase
and life-
cycle costs. Here, the compressor must satisfy extremely different demand
profiles de-
pending on the operating state of the rail vehicle. The typical problem in
designing a
compressor is that of finding the best comprise between these demands which is
ac-
ceptable in all operating states of the rail vehicle. In general, electrically
driven com-
pressors are used in rail vehicles. The operation of the compressors takes the
form of
on/off operation with a constant rotational speed, the so-called rated
rotational speed,
between the lower activation pressure and the upper deactivation pressure. The
compres-
sor is dimensioned such that a predefined filling time is attained and a
minimum activa-
tion duration during operation is not undershot.
From the generally known prior art, it emerges that, between the different
operating
states of the rail vehicle, there is no difference in the operation of the
compressor. Here,
the fan of the cooling system is subject to the same operating regime as the
compressor,
as the fan is generally directly jointly driven by the compressor.
It is also known that a more complex construction and more complex operation
of the
compressor system in relation to regular operation and in relation to the
regular con-
struction necessitate additional, in particular electronic components which
may exhibit
additional probability of failure or at least additional susceptibility to
failure. In other
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words, the incorporation of additional electronics components in the
compressor system
also introduces into the compressor system the additional probability of
failure of the
individual electronics components. The probability of faults and the risk of
failure of the
compressor system are thus increased. Since the compressor system supplies
compressed
air to the brake system, a failure of the compressor system generally has the
effect of
bringing the rail vehicle to a standstill.
DISCLOSURE OF THE INVENTION
It is therefore the object of the present invention to optimize a compressor
system and a
method for operating the compressor system such that more energy-efficient
operation
of the compressor system, with a reduction in sound emissions, is possible
without an
increase in the probability of faults and risk of failure of the compressor
system.
With regard to a device, the object is achieved, proceeding from a compressor
system as
per the preamble of Claim 1, in conjunction with the characterizing features
of said
claim. With regard to a method, the object is achieved as per Claim 6 in
conjunction
with the characterizing features thereof. Advantageous refinements of the
invention
emerge from the following dependent claims.
According to the invention, an actuator for the continuous manipulation of the
rotational
speed of the electric machine is arranged between an electrical supply and the
electric
machine, wherein the actuator can be controlled by way of the regulation
device, and
wherein, in the compressed air-conducting line arranged downstream of the
compressor,
there is arranged a pressure switch for monitoring of the pressure in the at
least one
compressed-air vessel and for manipulation of at least the rotational speed of
the electric
machine.
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In other words, the actuator is situated upstream of the electric machine in
the power
flow, and is thus positioned ahead of the electric machine. The actuator
permits opera-
tion of the electric machine at different rotational speeds. Frequency
converters or in-
verters are particularly suitable for this purpose. In a manner dependent on
frequency,
the rotational speed of the electric machine and thus the operation of the
compressor are
adapted. However, the additional electronic components for regulating the
rotational
speed, in particular the additional sensors, cables and the actuator, give
rise to an in-
crease in the probability of faults and risk of failure of the compressor
system.
By means of the pressure switch for monitoring the pressure in the at least
one com-
pressed-air vessel, the reliability of a compressor system of said type is
increased, and
the possibility of reliable emergency running operation is realized.
Specifically, in the
event of a drop in pressure, the pressure switch can indirectly manipulate at
least the
rotational speed of the electric machine. By means of a signal from the
pressure switch
to the effect that a certain lower pressure in the at least one compressed-air
vessel has
been undershot, the compressor can be activated, and in particular the
rotational speed of
the compressor can be increased, in order to increase the pressure in the at
least one
compressed-air vessel up to a certain upper pressure. Thus, the pressure
switch manipu-
lates at least the rotational speed of the compressor only when the pressure
reaches ei-
ther the minimum pressure or the upper deactivation pressure. When the minimum
pres-
sure is reached, the rotational speed is increased, wherein, when the upper
deactivation
pressure is reached, it is at least the case that the rotational speed is
reduced, or the com-
pressor is deactivated. In other words, in the event of a fault in the
compressor system
which leads to the minimum pressure in the at least one compressed-air vessel
being
reached, regular operation of the compressor is resumed such that the
compressor is op-
erated at rated rotational speed.
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In a preferred exemplary embodiment, the pressure switch is operatively
connected to
the regulation device for the purposes of indirect manipulation of the
rotational speed of
the electric machine. In other words, the pressure switch transmits the
generated signals
to the regulation device, wherein the latter, preferably by way of an
integrated control
algorithm, adapts the rotational speed of the electric machine to the received
signal.
In a further preferred exemplary embodiment, an isolating switch for
separating the reg-
ulation device and the actuator from the electric machine is connected
downstream of
the actuator. In this case, the isolating switch is in particular arranged
between the elec-
trical supply and the electric machine, and thus constitutes a bridge both
between the
actuator and the electric machine and between the electrical supply and the
electric ma-
chine.
Furthermore, the pressure switch is preferably connected to the isolating
switch via an
interposed control logic unit. The isolating switch is consequently
independent of the
regulation device and can be operated by way of the control logic unit, which
receives
signals from the pressure switch.
It is preferably provided that the regulation device at least indirectly
controls a cooler
unit which is arranged downstream of the compressor and which has a cooler
fan,
wherein a rotational speed of the cooler fan can be continuously adjusted by
the regula-
tion device. For this purpose, an actuator is preferably integrated in the
cooler unit. It is
alternatively also conceivable for the actuator to be at least positioned
upstream of the
cooler unit. It is likewise conceivable for an actuator to have two control
outputs, such
that both the electric machine and the cooler fan are controlled by way of a
common
actuator.
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With regard to the method, the compressor is operated with a variable
rotational speed
which assumes any intermediate value between the maximum rotational speed and
the
minimum rotational speed, wherein the pressure switch monitors the pressure in
the at
least one compressed-air vessel and indirectly manipulates at least the
rotational speed
of the electric machine. By virtue of the fact that the cooling unit is not
connected either
directly or indirectly to the compressor, separate control of the cooling unit
and thus
separate adjustment of the rotational speed of the cooler fan are performed.
It is advan-
tageously also possible for the compressor and the cooler fan to be
deactivated.
In a further exemplary embodiment, when the minimum pressure in the at least
one
compressed-air vessel is reached, the regulation device receives from the
pressure switch
a signal for triggering the actuator to operate the compressor at at least the
rated rota-
tional speed until the deactivation pressure is reached. In this way, it is
possible in par-
ticular to counteract faulty sensors and/or cables. Specifically, the
regulation device con-
trols the actuator in accordance with the output of the pressure switch.
In a further exemplary embodiment, when the minimum pressure in the at least
one
compressed-air vessel is reached, the control logic unit receives from the
pressure switch
a signal for triggering the isolating switch and separating the regulation
device and the
actuator from the electric machine, wherein the compressor is operated, via
the isolating
switch, with the rated rotational speed until the deactivation pressure is
reached. De-
pending on the position of the isolating switch, it is also possible to
generate a rotational
speed higher than the rated rotational speed for the electric machine. For
this purpose,
the isolating switch connects the electric machine directly to the electrical
supply.
Therefore, the regulation device cannot have any influence on the electric
machine and
thus on the rotational speed of the compressor. In this way, it is possible in
particular for
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a failure or a fault of the regulation device as a whole, together with all
associated sen-
sors and the actuator, to be counteracted.
It is particularly preferably provided that, after the pressure of the at
least one corn-
pressed-air vessel has fallen to the minimum pressure at least twice, the
electric machine
is operated with intermittent alternation between at least the rated
rotational speed when
the pressure falls to the minimum pressure and deactivation of the compressor
when the
deactivation pressure is reached. In other words, the rotational speed of the
electric ma-
chine and thus the rotational speed of the compressor are varied no further,
in order to
maintain a relatively constant pressure in the at least one compressed-air
vessel. It is
however also conceivable for the compressor to be operated not with the rated
rotational
speed but with a maximum rotational speed in order to permit faster filling of
the at least
one compressed-air vessel.
BRIEF DESCRIPTION OF THE DRAWINGS
Further measures which improve the invention will be presented in more detail
below in
conjunction with the description of preferred exemplary embodiments of the
invention
and with reference to the figures, in which:
figure 1 shows a block circuit diagram of the compressor system
according to the
invention,
figure 2 shows a block circuit diagram of the compressor system
according to the
invention as per a second exemplary embodiment, and
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figure 3 shows two related diagrams, wherein a rotational speed of the
compressor
is plotted versus time in the upper diagram, and a pressure of the compressor
is
plotted versus time in the lower diagram.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
As per figure 1, a compressor system for a rail vehicle has an electric
machine 1 which,
via a drive shaft 2, drives a compressor 3 for generating compressed air. The
compressed
air generated by the compressor 3 is conducted via a compressed air-conducting
line 6 to
a cooler unit 9 which has a cooler fan 14. A pressure sensor 7 and a
temperature sensor
13b are arranged downstream of the cooler unit 9 in the compressed air-
conducting line
6. Furthermore, the compressed air-conducting line 6 issues into a pre-
separator 11,
downstream of which there is connected an air treatment system 12. The dried
com-
pressed air, which has been purified of particles, is then fed into a
compressed-air vessel
4. Furthermore, in the compressed-air conducting line 6, there is arranged a
pressure
switch 16 for the monitoring of the pressure in the compressed-air vessel 4
and for the
indirect manipulation of the rotational speed of the electric machine 1 and of
the cooler
fan 14.
A temperature sensor 13a, which is arranged at the compressor 3, and the
temperature
sensor 13b and the pressure sensor 7 all transmit the measured temperatures
and the
measured pressure to the regulation device 5. Furthermore, via a signal input
10, the
regulation device 5 also receives signals from other sensors ¨ not illustrated
here ¨ or
from a train management system. Furthermore, the regulation device 5 is
suitable for
both controlling the rotational speed of the cooler unit 9 and transmitting
signals to an
actuator 8. The actuator 8, which is in the form of a frequency converter,
sets the rota-
tional speed of the electric machine 1 and thus the rotational speed of the
compressor 3.
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Furthermore, the actuator 8 has two outlets and thus also sets the rotational
speed of the
cooler fan 14 by way of the regulation device 5. In this case, the actuator 8
is, for the
continuous manipulation of the rotational speed of the electric machine 1,
arranged be-
tween an electrical supply 15 and the electric machine 1. In this case, when a
minimum
pressure e in the compressed-air vessel 4 is reached, the regulation device 5
receives
from the pressure switch 16 a signal for triggering the actuator 8 to operate
the compres-
sor 3 at the rated rotational speed n until a deactivation pressure d is
reached.
In Figure 2, an isolating switch 17 for separating the regulation device 5 and
the actuator
8 from the electric machine 1 is connected downstream of the actuator 8. The
pressure
switch 16 is connected to the isolating switch 17 via an interposed control
logic unit 18.
In this case, when a minimum pressure e in the compressed-air vessel 4 is
reached, the
control logic unit 18 receives from the pressure switch 16 a signal for
triggering the iso-
lating switch 17 and separating the regulation device 5 and the actuator 8
from the elec-
tric machine 1. The compressor 3 is then operated, via the isolating switch
17, at the
rated rotational speed n until a deactivation pressure d is reached.
Figure 3 graphically illustrates the above-described process in the event of a
pressure
drop in the compressed-air vessel 4 being measured by way of the pressure
switch 16. In
a region a, the compressor 3 is operated at a rotational speed between a
minimum rota-
tional speed i and the rated rotational speed n, wherein the pressure in the
compressed-
air vessel 4 is kept in a certain range. Thus, in the region a, the compressor
3 is in regu-
lated operation. The rotational speed is variable and dependent on the
situation.
In a region b, the pressure in the compressed-air vessel 4 and the rotational
speed of the
compressor 3 spontaneously drop. In other words, in the region b, a fault has
occurred
during regulated operation, which fault has led to a measured pressure drop.
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When the pressure in the compressed-air vessel 4 reaches the minimum pressure
e, the
pressure switch 16 reacts and, in a region c, increases the rotational speed
of the electric
machine 1 and thus the rotational speed of the compressor 3 to the rated
rotational speed
n indirectly, either via the isolating switch 17 or via the actuator 8.
Consequently, in the
region c, the reaction of the pressure switch 16 occurs for the switchover of
operation
from regulated operation to non-regulated operation. There are two states of
non-
regulated operation. These are firstly the operation of the compressor 3 at
the rated rota-
tional speed n, and secondly the deactivation of the compressor 3. The cooler
fan 14 (not
illustrated here) is also operated analogously to the operation of the
compressor 3.
After a deactivation pressure d has been reached in the compressed-air vessel
4, the
compressor 3 is deactivated and is operated once again at a rotational speed
between the
minimum rotational speed i and the rated rotational speed n, such that the
pressure in the
compressed-air vessel 4 is kept in a certain range.
The invention is not restricted to the preferred exemplary embodiments
described above.
Rather, modifications thereto are also possible which are also encompassed by
the scope
of protection of the following claims. For example, it is also possible for
the compressor
3 to provide a feed to a multiplicity of compressed-air vessels 4. It may also
be provided
that, when the minimum pressure e in the compressed-air vessel 4 is reached,
the rota-
tional speed of the electric machine 1 and thus the rotational speed of the
compressor 3
are increased to a maximum rotational speed m rather than just the rated
rotational speed
n.
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List of reference signs
1 Electric machine
2 Drive shaft
3 Compressor
4 Compressed-air vessel
5 Regulation device
6 Compressed air-conducting line
7 Pressure sensor
8 Actuator
9 Cooler unit
10 Signal input
11 Pre-separator
12 Air treatment system
13a, 13b Temperature sensor
14 Cooler fan
15 Electrical supply
16 Pressure switch
17 Isolating switch
18 Control logic unit
a, b, c Region
d Deactivation pressure
e Minimum pressure
i Minimum rotational speed
m Maximum rotational speed
n Rated rotational speed
