Abstract:
A rail vehicle compressor system and method for controlling the same use a compressor driven by an electrical machine via a drive shaft, to produce compressed air for at least one compressed air tank, wherein the electrical machine can be activated at least indirectly via a control device for operating the electrical machine at at least one nominal speed between a maximum speed and a minimum speed, wherein at least one pressure sensor determines the pressure for the control device and is disposed in a compressed-air-carrying line downstream of the compressor. A final control element continuously influences the speed of the electrical machine and can be activated via the control device, and wherein a pressure switch for monitoring the pressure in the at least one compressed air tank and for influencing at least the speed of the electrical machine is disposed in the compressed-air-carrying line downstream of the compressor.

Description:
PRIORITY CLAIM 
       [0001]    This patent application is a U.S. National Phase of International Patent Application No. PCT/EP2014/076166, filed 2 Dec. 2014, which claims priority to German Patent Application No. 10 2013 113 557.9, filed 5 Dec. 2013 the disclosure of which are incorporated herein by reference in their entirety. 
     
    
     FIELD 
       [0002]    The disclosed embodiments relate 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 using a regulation device for operation of the electric 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 for determining the pressure for the regulation device. The disclosed embodiments relate to a method for controlling the compressor system according to at least one of the disclosed embodiments. 
       BACKGROUND 
       [0003]    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 depending 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 acceptable in all operating states of the rail vehicle. In general, electrically driven compressors 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 compressor is dimensioned such that a predefined filling time is attained and a minimum activation duration during operation is not undershot. 
         [0004]    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. 
         [0005]    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 construction necessitate additional, in particular electronic components which may exhibit additional probability of failure or at least additional susceptibility to failure. In other 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. 
       SUMMARY 
       [0006]    It is therefore the object of the present disclosed embodiments 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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Disclosed embodiments are explained more specifically below with reference to the accompanying drawings, in which: 
           [0008]      FIG. 1  shows a block circuit diagram of the compressor system according to the disclosed embodiment, 
           [0009]      FIG. 2  shows a block circuit diagram of the compressor system according to at least one disclosed embodiment, and 
           [0010]      FIG. 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 
       [0011]    According to at least one disclosed embodiment, 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. 
         [0012]    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 operation of the electric machine at different rotational speeds. Frequency converters or inverters 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 increase in the probability of faults and risk of failure of the compressor system. 
         [0013]    Using the pressure switch for monitoring the pressure in the at least one compressed-air vessel, the reliability of a compressor system of the 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. Using 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, to increase the pressure in the at least one compressed-air vessel up to a certain upper pressure. Thus, the pressure switch manipulates at least the rotational speed of the compressor only when the pressure reaches either the minimum pressure or the upper deactivation pressure. When the minimum pressure 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 compressor 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 operated at rated rotational speed. 
         [0014]    In at least one disclosed 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, may be by way of an integrated control algorithm, adapts the rotational speed of the electric machine to the received signal. 
         [0015]    In at least one disclosed embodiment, an isolating switch for separating the regulation 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 electrical 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 machine. 
         [0016]    Furthermore, the pressure switch may be 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. 
         [0017]    In accordance with at least one embodiment 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 regulation device. For this purpose, an actuator may be 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. 
         [0018]    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 advantageously also possible for the compressor and the cooler fan to be deactivated. 
         [0019]    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 rotational speed until the deactivation pressure is reached. In this way, it is possible in particular to counteract faulty sensors and/or cables. Specifically, the regulation device controls the actuator in accordance with the output of the pressure switch. 
         [0020]    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. Depending 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 a failure or a fault of the regulation device as a whole, together with all associated sensors and the actuator, to be counteracted. 
         [0021]    In accordance with at least one embodiment provided that, after the pressure of the at least one compressed-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 machine and thus the rotational speed of the compressor are varied no further, 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 to permit faster filling of the at least one compressed-air vessel. 
         [0022]    As per  FIG. 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  13   b  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 compressed 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 . 
         [0023]    A temperature sensor  13   a , which is arranged at the compressor  3 , and the temperature sensor  13   b  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 rotational speed of the electric machine  1  and thus the rotational speed of the compressor  3 . 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 between 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 compressor  3  at the rated rotational speed n until a deactivation pressure d is reached. 
         [0024]    In  FIG. 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 isolating switch  17  and separating the regulation device  5  and the actuator  8  from the electric 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. 
         [0025]      FIG. 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 rotational 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 regulated operation. The rotational speed is variable and dependent on the situation. 
         [0026]    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. 
         [0027]    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 rotational 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 . 
         [0028]    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. 
         [0029]    The disclosed embodiments are not restricted to the 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 rotational 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. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           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 
           13   a ,  13   b  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