Patent Publication Number: US-2009220338-A1

Title: Fluid Compressor with Aerostatic Bearing, Control System of a Compressor with Aerostatic Bearing and Method of Controlling a Compressor with Aerostatic Bearing

Description:
The present invention relates to a fluid compressor having an aerostatic bearing, to a control system of a fluid compressor having an aerostatic bearing as well as to a method of controlling a compressor, this fluid compressor may include, for instance, centrifugal compressors or linear compressors applicable to cooling systems and to the construction and the respective control system of the pressurization in the bearings of said devices. 
     DESCRIPTION OF THE PRIOR ART 
     Centrifugal compressors have long been used in the industry, for instance, in the automotive industry. Its concept is quite simple in relation to the other compressors, e.g., reciprocating, rotary etc. However, their bearing system is highly complex due to high speed operation during the normal functioning mode, which is estimated at a rotation of about 30,000 to 200,000 rpm. Notedly, the use of centrifugal compressors in cooling cycles has been rare, due to the technological difficulties for the bearing system. 
     Still with regard to the centrifugal compressors, these normally have single or double stage configurations, but they may include multiple stages according to the use of the equipment, the amount of stages being defined by the number of rotors mounted on an shaft with actuation by an electrical motor. 
     According to the prior art, one of the ways to solve the bearing system problem for shaft floating is the use of electromagnetic bearings that keep the shafts floating in view of obtain a construction which has no friction in the bearings. This solves the problem of friction, but requires a specific electric circuit, and the bearing needs to be provided with energizable coils to form the electromagnetic field. 
     Other solutions describe the use of aerostatic bearings that are pressurized to float during the operation of the compressor and thus reduce friction and prolong the useful life of the equipment. In these solutions, it is necessary to use, for instance, a pump so that the bearing is pressurized at the moment in which the compressor is turned on (or is at starting mode) to avoid premature wear of the equipment. 
     One of the solutions found in the art that tries to solve these problems is described in document EP 0 212 091, which refers to a pressurized bearing that is used in turbochargers of internal-combustion engines. According to the teachings of this document, a storage reservoir connected between the hot and the cold part of the turbocharger is provided, and this reservoir stores the air pressurized by the turbocharger in order to pressurize the bearing and, thus, avoid its wear during the start and operation of the engine. 
     One of the deficiencies of this solution is that it requires the assembly of a reservoir and piping, which generates manufacturing and maintenance costs. 
     BRIEF DESCRIPTION AND OBJECTIVES OF THE INVENTION 
     In order to overcome the problems of the prior art, the objects of the present invention are a compressor, a system and the respective method of control with a bearing system through a previously pressurized reservoir, controllable by a pair of control valves aiming at:
         Achieving a simplified bearing system;   Eliminating the whole electric-electronic control system of the electromagnetic bearings of the current models;   Lowering the cost of the product;   Making it a more competitive product;   Making it a simpler product for large-scale manufacture, and   Reducing the volume of the compressor.       

     These objectives are achieved by means of a fluid compressor comprising a pressurization chamber and at least one fluid pressurization device, the pressurization chamber and the pressurization device being inside a housing, the pressurization chamber having a non-pressurized inlet and a pressurized outlet, the pressurization device compressing the fluid collected by the non-pressurized inlet and discharging it through the pressurized outlet, the pressurization device having at least one aerostatic bearing, the aerostatic bearing comprising a floating pressurization region, the compressor comprising a compressed fluid accumulator fluidically connectable to the pressurized outlet and to the floating pressurization region, the compressed fluid accumulator being located inside the compressor housing. 
     The objectives of the present invention are further attained by a compressor control system that comprises a control circuit to control a fluid compressor, the compressor comprising a pressurization chamber and at least one fluid pressurization device, the pressurization chamber and the pressurization device being located in a housing, the pressurization chamber having a non-pressurized inlet and a pressurized outlet, the pressurization device compressing the fluid collected by the non-pressurized inlet and discharging it through the pressurized outlet, the pressurization device having at least one aerostatic bearing, the aerostatic bearing comprising a floating pressurization region, the system further comprising a first control valve and a second control valve that selectively connect either a compressed fluid accumulator integrated into the housing with pressurized outlet or the compressed fluid accumulator to the floating region of the aerostatic bearing, the system being configured to connect the compressed fluid accumulator to the pressurized outlet and the floating region of the aerostatic bearing when the compressor is operating, or only the compressed fluid accumulator and the floating region of the aerostatic bearing before the start of the compressor. 
     Still according to the teachings of the present invention, the objectives are further achieved by a method of starting a compressor that comprises the steps of: in the start mode, opening a passage from the compressed fluid accumulator during the time needed for an aerostatic bearing of the compressor to float; keeping the second control valve closed until the pressure of the pressurized outlet is higher than the pressure of the fluid discharged from the compressed fluid accumulator; recharging the compressed fluid accumulator from the fluid at the pressurized outlet. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will be described in more details on the basis of embodiments examples represented in the drawings. The drawings show: 
       FIG.  1 —is a schematic cut view of a multiple-stage centrifugal compressor, illustrating one of the embodiments of the present invention; 
       FIG.  2 —is a schematic cut view of a multiple-stage centrifugal compressor, illustrating one of the embodiments of the present invention; 
       FIG.  3 —is a cut view of a linear compressor, according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF DRAWINGS 
     As can be seen in  FIGS. 1 and 2 , one of the possible embodiments of the teachings of the present invention is to apply them to a centrifugal compressor, for instance, of the two-stage type. This type of compressor has two stages, whose compression rotor  1 , of the first stage, has the function of drawing a fluid (gas) through a non-pressurized inlet  10 ; in order to be pressurized then by a second-stage compression rotor  2  for the cooling circuit (not shown) from the pressurized outlet  20 . The two compression rotors  1 ,  2  are associated, that is to say, they are mechanically fixed at the ends of a same shaft  6 , which is, in turn, activated by an electric motor  7 . Shaft  6  also has a pair of aerostatic bearings  3  in a floating pressurization region  33  which, when submitted to a positive pressure, start to float. 
     In addition, compressor  100  further consists of a housing  4 , which comprises an external wall or closure walls  44  that make the compressor  100  hermetically closed. 
     Another embodiment of the present invention is applicable to linear compressors and, in this case, the difference is related to the bearing system of the piston  18  itself, instead of a shaft  6  that is present in centrifugal compressors. As can be observed in more details in  FIG. 3 , in a linear compressor, the pressurization device is a piston  18  positioned inside a cylinder  19 , the piston  18  being displaceable inside the cylinder  19  by an electric motor  7  of the linear type, the piston  18  further resting on a pair of aerostatic bearings  3 . 
     Generically, the same constructive concepts may be applied to centrifugal and linear compressors, since both have conceptually the same means of operation. In both cases, at least one pressurization chamber C is foreseen where the fluid will be compressed by at least one fluid pressurization device  1 ,  2 ,  18 , that is to say, by one or more rotors  1 ,  2  or a piston  18 , which, independently of the solution, will be located in a housing  4 , the pressurization chamber C having a non-pressurized inlet  10  and a pressurized outlet  20 , the fluid (gas) being collected by the non-pressurized inlet  10 , compressed in the pressurization chamber C and discharged through the pressurized outlet  20 . 
     For both the bearings in the centrifugal compressor and in the linear compressor to float, at least one aerostatic bearing  3  is provided, this aerostatic bearing  3  comprising a floating pressurization region  33  to where the fluid must be pumped for the bearing to float during the operation of the compressor  100 . 
     According to the teachings of the present invention in order to overcome the constructive and operating problems in the art, a reservoir (or a compressed fluid accumulator  5 ) must be provided, which may be fluidically connected to the pressurized outlet  20  and to the floating pressurization region  33 , so as to (i) make the aerostatic bearings  3  float during the operation of the compressor  100  and, at the same time, ii) feed the compressed fluid accumulator  5  with the pressure available at the pressured outlet  20 . 
     In addition, so as to overcome the space, construction, maintenance and manufacturing problems of the prior art, the compressed fluid accumulator  5  must be located inside the housing  4  within the respective closure walls  44 , so that it is formed as an integral part of the housing  4 , which imparts not only less charge loss, but also a more immediate response in the recharge of the compressed fluid accumulator  5  and, therefore, more efficiency, and in the pressurization of the bearings  3 . 
     With regard to the fluid connections between the compressed fluid accumulator  5 , the pressurized outlet  20  and the floating pressurization region  33  of the aerostatic bearing  3 , it is possible to observe from  FIGS. 1 and 2  that the compressed fluid accumulator  5  is selectively connectable either to the pressurized outlet  20  or to the floating region  33  of aerostatic bearing  3 . In this sense, it is possible to observe that the compressed fluid accumulator  5  is connectable to the floating region  33  of the aerostatic bearing  3  through an accumulator tube  32  and a bearing tube  31 , the accumulator tube  32  being connected to the bearing tube  31  through a first control valve  8 , the first control valve  8  being located in the accumulator tube  32 . The connection of the compressed fluid accumulator  5  with the pressurized outlet  20  is made by the accumulator tube  32  and a collection tube  30 , the accumulator tube  32  being connected to the collection tube  30  through the first control valve  8  and a second control valve  9 , this second control valve  9  being located in the collection tube  30 . 
     Operationally, the first control valve  8  enables the connection of the compressed fluid accumulator to the pressurized outlet  20  when the compressor  100  is operating, and the floating pressurization region  33  of the aerostatic bearing  3  is also connected to the pressurized outlet when the compressor  100  is operating, for the compressed fluid accumulator  5  to have the same pressure of the pressurized outlet  20  and, thus, remain charged. 
     With this configuration, before the start of the compressor  100 , the compressed fluid accumulator  5  is connected to the floating pressurization region  33  of the aerostatic bearing  3 , the second control valve  9  remaining closed to the passage of the fluid to the pressurized outlet  20 , the compressor  100  only being started after the time needed for the aerostatic bearing  3  to float, which usually takes approximately one second. 
     With regard to the type of valve, preferably as a first control valve  8  an electric valve (or solenoid valve) is used that can be controlled by an external system, according to the teachings of the present invention, so as to release the fluid stored in the compressed fluid accumulator  5  at the start of the compressor  100 , as well as to control the respective recharge during the operating phase of the compressor  100 . 
     With regard to the second control valve  9 , this is preferably the unidirectional mechanical valve that enables the passage of the fluid of the pressurized outlet  20  to the compressed fluid accumulator  5 . This unidirectional valve aims at preventing the fluid that is stored in the compressed fluid accumulator  5  from exiting through the pressurized outlet  20  when the compressor  100  is at the starting phase and, at the same time, must be configured to be open to the passage of the pressurized fluid at the pressurized outlet  20  for recharging the compressor  100  when the latter is in operation. The second control valve  9  can also be replaced by an electric valve (or solenoid valve) that must be opened in the suitable moments to achieve the objectives of the present invention. 
     In order to control the compressor  100  of the present invention, an associated system is provided. The system must comprise an electronic control circuit  88  to control the starting phase of the compressor  100  as well as the charging phase of the compressed fluid accumulator  5 . Therefore, as already mentioned, the control circuit  88  of the system of the present invention must selectively connect, by means of the first control valve  8  and the second control valve  9 , either the compressed fluid accumulator  5  to pressurized outlet  20  or the compressed fluid accumulator  5  to the floating region  33  of the aerostatic bearing  3  and, specifically, it must be configured to connect the compressed fluid accumulator  5  to the pressurized outlet  20  and the floating region  33  of the aerostatic bearing  3  when compressor  100  is operation, or only the compressed fluid accumulator  5  and the floating region  33  of the aerostatic bearing  3  before the start of the compressor  100 . 
     The system must further provide that, at the start of the compressor  100 , the control circuit  88  opens the electric valve so that the compressed fluid stored inside the compressed fluid accumulator  5  is, at least partially, transferred to the floating pressurization region  33  of the aerostatic bearing  3  and the compressor  100  is started only after the time needed for the aerostatic bearing  3  to float, that is, typically within approximately one second after the opening of the compressed fluid accumulator  5 . At this moment, the second control valve  9  will remain closed for the passage of the fluid to the pressurized outlet  20 , until the pressure of the fluid of the pressurized outlet  20  is higher than the pressure of the fluid discharged from the compressed fluid accumulator  5 . 
     By applying the operation of the system to the compressor  100 , the following steps can be foreseen for the start of the compressor:
         in the start mode, opening a passage from the compressed fluid accumulator  5  during the time needed for the aerostatic bearings  3  of the compressor  100  to float; and   keeping the second control valve  9  closed until the pressure of the pressurized outlet  20  is higher than the pressure of the fluid discharged from the compressed fluid accumulator  5 ; and   recharging the compressed fluid accumulator  5  from the fluid at the pressurized outlet  20 .       

     Preferably, the volume of the compressed fluid accumulator is configured to have about 10% of the total volume of the refrigerant fluid that circulates inside the cooling circuit, other volume percentages also being possible, depending on the conditions and characteristics of the compressor  100 . In comparison with the systems according to the prior art, the advantages are significant, since not only a reduced size is achieved for the installation of the compressor  100  of the cooling system but also a reduced mounting time of the compressor  100  at a refrigerator cabinet is attained, for instance, because the compressed fluid accumulator  5  is already integrated into the housing  4 , and, in addition, cost sayings are achieved because the volume of the cooling fluid is smaller when compared to a system with a reservoir separated from the housing  4 , which results in lower manufacturing and maintenance costs of the compressor  100 . 
     After having described examples of the preferred embodiment, it must be understood that the scope of the present invention encompasses other possible variations, being limited only by the content of the appended claims, including therein the possible equivalents.