Abstract:
A dry running gas compressor has at least a first compression unit with a housing and a first working chamber in which gas is compressed. A hollow of said first working chamber is in said housing. A closed cooling liquid circuit is adapted for cooling the first working chamber of the first compression unit. The compression unit has at least one lubricant channel through which lubricant is guided to a bearing or gearbox or other component of the first compression unit. The lubricant channel is part of a lubricant circuit. The lubricant circuit is effectively fluidly separated from the cooling circuit.

Description:
FIELD OF INVENTION 
       [0001]    The present invention refers to a dry running compressor for creating compressed gas such as air. 
       BACKGROUND OF INVENTION 
       [0002]    Dry running compressors generally comprise one or more compression units each of which can be called a stage. Whether the compressor is a one-stage or a multi-stage pump, and the type of construction of the stages, depends on the demands for the required amount of compressed air and the ultimate pressure to be reached. Usually, the compression units are driven by a motor. 
         [0003]    High-capacity compressors require efficient cooling of the compressor units because a significant amount of heat is generated when compressing gas such as air. The heat could lead to an overheating of the components of the compressor if there is insufficient cooling. Some systems use air cooling, whose performance can be improved for example by cooling plates or by a blower. In stationary compressors water cooling can be used. The water cooling often relies on an external cooling water system. The need for an external cooling water system can limit the ability to use such a cooling method when huge quantities of cooling water from an external cooling system are not available, for instance at certain sites where portable compressors are needed. 
         [0004]    In some compressors oil-free compressed air is needed. For instance in some applications the compressed air needs to be oil free so as to not soil components driven by the compressed air with a lubricant. Therefore oil circulating in the bearings and gearboxes of the compressor needs to be well-separated or encapsulated from the compressed air flow so the lubricant does not contaminate the compressed air flow. Also in the bearings and the gearboxes lubricated by oil or other liquid lubricant there are quite significant heat quantities occurring which need to be removed. 
         [0005]    A compressor installation having a frame is known from DE 103 46 518 A1. The compressor installation comprises at least one drive, one compression stage and a pressure vessel. In a preferred embodiment, a cooling module is provided which is not specified in detail. 
         [0006]    EP 1 451 469 B1 specifies a lubricant-cooled gas compressor for releasing a mixture of lubricant and compressed gas and having means for separating lubricant from the compressed gas. The compressor system, which allows the compressed air to mix with the lubricant, allows efficient heat removal, but requires appropriate technical provisions to regain the lubricant and the coolant from the compressed gas. If the compressed gas which is to be created needs to be completely free of lubricants and coolants, such cooling is not appropriate. 
       SUMMARY OF INVENTION 
       [0007]    It is one object of the present invention to provide a compressor for creating compressed air having an improved cooling system with a liquid cooling circuit to cool at least the compression unit without the necessity to be connected to an external cooling water system. It is also an object of the invention to provide an oil-free compressor to avoid the inflow of coolant and lubricant into the compressed air flow. Also, it is a further object of the invention to provide cooling of the lubricant which flows over the moving parts of the compressor with the liquid cooling circuit of the compressor. 
         [0008]    A compressor according to the invention is characterized by having a closed cooling liquid circuit interfaced with at least a first compression unit, which can alternatively be called a compression stage. The closed circuit comprises a liquid pump and a liquid cooler. The cooling liquid flowing through the cooling circuit provides for the cooling of the compression unit. 
         [0009]    Besides the first compression unit, the compressor can include a second compression unit which can also alternatively be called a second compression stage. The flow of the compressed gas from the first unit is in series with the compressed air flow of the of the second compression unit. The second compression unit or stage is also interfaced with the cooling circuit. Each compression stage, whether part of a single-stage or multi-stage pump (compressor) has a respective housing in which at least one cooling liquid channel is integrated therein, through which cooling liquid flows, and which is part of the closed cooling circuit. The cooling liquid, which can be water or a comparable heat transmission medium, is not injected into the actual hollows of the compression chambers of the compression units. It flows through a portion of the housings separated from the hollows of the compression chambers. For instance, surfaces of the housings delimiting the hollows of the chambers may separate the cooling liquid from the hollows. The compression chambers can alternatively be called working chambers. Various types of motor housings or pump housings are known from the state of the prior art which allow efficient heat removal by means of cooling liquid, so a detailed specification of the pump housing is not provided. 
         [0010]    In accordance with at least one embodiment of the invention the respective compression units or stages each have at least one lubricant channel through which lubricant, preferably oil, is guided to at least one component or part of each of the compression units such as a bearing or a gearbox or other moving part or component. Preferably, each compression unit has a plurality of lubricant channels to guide the lubricant to a plurality of parts, or components such as the gearboxes and bearings or other moving parts or components of the compression units, which require efficient lubrication, especially at high rotation speed. These lubricant channels are part of a lubricant circuit, which comprises a lubricant pump and a lubricant cooler. Heat from the parts lubricated such as the bearings and gearboxes and other parts interfaced with the bearings and gearboxes or other parts heated during operation of the compressor can be removed by the lubricant. 
         [0011]    An embodiment of the invention can further include the lubricant cooler having at least one cooling liquid channel and at least one lubricant channel. The cooling liquid channel is part of the cooling liquid circuit. The lubricant cooler includes a heat exchanger to provide for removal of the heat from the lubricant by the cooling liquid. The heat from the bearings and gearboxes is removed by the lubricant of the lubricant circuit flowing over the bearings and components of the gearboxes. The heat from the lubricant is removed by the cooling liquid of the cooling circuit flowing through the lubricant cooler. 
         [0012]    The compressor can be driven by different drive constructions. In many cases, it is suitable that a common drive motor drives both the first compressor unit as well as the second compressor unit. Furthermore, in modified embodiments, this motor can drive the lubricant pump and the cooling liquid pump, which, however, can also be equipped with separate drives. 
         [0013]    The drive motor or its housing, respectively, can also be included in the cooling water circuit, wherein cooling water channels are arranged in the housing of the drive motor. 
         [0014]    Further details, advantages and developments can be taken from the following specification of a preferred embodiment of the invention, with reference to the drawing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  shows a simplified block diagram of an embodiment of the compressor according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The compressor of  FIG. 1  comprises a first compression unit  01  drawing in ambient air through a suction regulator  02  and a suction filter  03  and compressing the same. The air is thus drawn in at an inlet. The first compression unit, which can alternatively be called a first compression stage, has a working chamber, which can also be called a compression chamber, in which the air is compressed. The working chamber has a hollow. The airflow within the compressor is indicated by chain dotted lines. A description of the connecting pipes and the flanges is not provided herein since the formation of these elements is not essential for the present invention. 
         [0017]    The air, pre-compressed by the first compression unit  01 , is guided through an intercooler  05  and a condensate separator  06  to a second compression unit  07 , in which the air is further compressed in a second working chamber to reach the desired ultimate pressure. The second working chamber can also be called a second compression chamber. The chamber has a hollow. Then, the created compressed air is provided through a non-return valve  09 , an aftercooler  10  and a further condensate separator  06  for discharge to, for example, compressed air driven tools. 
         [0018]    A closed cooling liquid circuit, which cools at least the compression units  01 ,  07 , is provided. The circuit removes the heat from the compression units. The closed circuit is a cooling water circuit. The closed cooling water circuit comprises a liquid cooler  11  and a liquid pump  12 . The pump  12  is a water pump and the cooler  11  is a water cooler. The pipes of the closed cooling water circuit are indicated in the block diagram by continuous lines. The cooling water circuit includes a plurality of cooling water channels in each of the respective housings of the first, and respectively, of the second compression units  01 ,  07 . In the block diagram, the plurality of cooling water channels is not indicated separately. They carry the cooling liquid in the cooling circuit to provide cooling of the compression units, especially the working chambers of the compression units, in which the actual compression work is performed. The circuit removes heat from the compression units especially their working chambers. The cooling water channels are preferably arranged at and in the portions of the housings in which the hollows of the working chambers or compression chambers are disposed, so that the cooling water circulates around the hollows of the working chambers, without, however, having to be injected into or going into or entering into the hollows of the compression chambers. The cooling water channels may pass into and through portions of the housings forming the compression units but are separated from and separate from the hollows of the working chambers. For instance, inner surfaces of the housings of the compression units delimiting the hollow of each working chamber may separate the liquid cooling channels from the hollows of the working chambers. The hollows of the working chambers do not form a portion of channels forming the cooling water circuit and do not form part of the cooling water circuit. The reverse is also true. The circuit does not have a discharge opening emptying into said hollows of said working chambers. 
         [0019]    In the block diagram as shown, the cooling liquid, which in this case is water, of the cooling circuit, sequentially flows through the, respective housings of the compression units  01 ,  07 . It is possible that structure such as piping forming a channel of the cooling circuit has a surface that delimits at least a portion the hollow of each or one of the working chambers. Preferably, the order of the units to be cooled by the cooling water circuit is chosen so that depending on the temperatures, efficient cooling can be realized. Thus, in many embodiments it may be advantageous to first guide the cooling water, from the water cooler  11 , to the second compression unit  07 , since from there, a greater amount of heat removal is needed. The water of the water circuit flows from the second unit  07  to the first unit  01 . According to the attached block diagram of  FIG. 1 , cooling water in the cooling circuit then flows from the first unit through a lubricant cooler  15 , whose functionality is described below, wherefrom the cooling water is led back to the water cooler  11 . The closed cooling circuit is thus a recirculating liquid circuit. The circuit forms at least one continuous channel in which the cooling liquid flows in a path as described by reference to the above cooling liquid channels and cooling liquid circuit. 
         [0020]    In an alternative embodiment, however, the compression units  01 ,  07  could be cooled in parallel as opposed to the above described in series pathway. The water cooler itself is cooled by an airstream that can actively be created by a fan  13 . 
         [0021]    In the shown embodiment, the compressor according to the invention furthermore comprises a lubricant circuit which is indicated in the block diagram by broken lines. Parts of the lubricant circuit include the lubricant cooler  15  as aforementioned, a lubricant pump  16  and a lubricant reservoir  17 . Preferably, oil is used as lubricant, which is guided to the compression units  01 ,  07  through respective lubricant connections  18 . There, the lubricant reaches bearings and gearboxes of the units which are to be lubricated. Besides the lubricating function, the lubricant also provides for cooling of the bearings and gearboxes of the units and other components and parts heated and lubricated during operation of the pump, especially moving parts. The heat from these items is removed by the lubricant as it passes over these items carrying away heat dissipated from these items. The liquid of the cooling circuit flowing at the lubricant cooler  15  cools the lubricant. The heat from the lubricant is removed by the coolant in the cooling circuit. The liquid coolant carries away heat dissipating from the lubricant. More particularly the lubricant cooler  15  comprises a heat exchanger that acts a medium to allow the coolant in the cooling circuit to carry away the heat dissipating from the lubricant as it passes through the lubricant cooler. The cooling liquid in the cooling circuit is cooled by the water cooler  11 . The heat from the coolant is removed by operation of the water cooler. Although the invention refers to an air compressor it more broadly covers any gas compressor including without limitation an air compressor. The term gas as used herein is broad enough to include ambient air, treated air, non-air compressible fluids, and mixtures of these.