Abstract:
A machine ( 1 ) has a rotor ( 3 ) located so that it can rotate in a housing ( 2 ). The rotor is located at least partly in fluid, such as coolant. To provide a machine which has lower losses with a higher cooling capacity, the housing pressure can be reduced so that the fluid transitions into the two-phase range. In one embodiment, the housing pressure can be reduced by a suction device ( 7 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to German Application No. 10 2005 038 273.8, filed Aug. 12, 2005, and German Application No. 10 2005 036 307.5, filed Aug. 2, 2005, both of which applications are herein incorporated by reference in their entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to a machine with a rotor that is located so that it can rotate in a housing. The rotor is located at least partly in fluid, such as a coolant.  
         [0004]     2. Technical Considerations  
         [0005]     On similar machines of the known art, a housing pressure of at least 1.5 bar is built up in the housing by means of suitable resistances in an outlet line that leads from the housing to a reservoir. On machines of this type where the housing is partly or completely filled with fluid, such as coolant, for example, the rotor rotates partly or completely in the fluid. High heat removal and, thus, high cooling capacity can be achieved and, thus, the machine can be operated at high output. At high speeds of rotation, however, high losses occur, in particular churning losses, on account of the viscous friction of the fluid, which, in turn, results in low efficiency of the machine.  
         [0006]     An object of this invention is to provide a machine of the general type described above but that has lower losses and higher cooling capacity than known machines.  
       SUMMARY OF THE INVENTION  
       [0007]     The invention teaches that the housing pressure can be reduced such that the fluid transitions into the two-phase range. According to the invention, therefore, the internal pressure in the housing is reduced, for example, to a value of less than approximately 0.8 bar, so that the fluid which is saturated at the ambient temperature transitions to super-saturation and releases gas. This resulting two-phase fluid having a liquid phase and a gas phase, where the area of separation of the phases is in the vicinity of the rotor, has significantly lower viscous friction. As a result of which, reduced losses, in particular churning losses, occur on the rotating rotor and, thus, the machine has a higher level of efficiency. The cooling capacity remains almost unchanged on account of the almost uniform and unchanging quantity of fluid.  
         [0008]     In one preferred non-limiting embodiment of the invention, the housing pressure can be reduced by means of a suction device. With a suction device, it is possible to easily generate a vacuum to reduce the pressure inside the housing.  
         [0009]     Preference is thereby given to a connection between an outlet line that is in communication with the housing and a suction side of the suction device.  
         [0010]     In one embodiment of the invention, the pressure side of the suction device can be connected with a reservoir. As a result, the suction device can easily be located in the outlet line that runs from the housing to the reservoir and is already present.  
         [0011]     In an additional advantageous embodiment of the invention, the pressure side of the suction device is realized in the form of a delivery line. With a suction line of this type, an additional user can therefore be supplied with fluid. If hydraulic fluid is used as the fluid, it thereby becomes possible with the suction device to supply another user with hydraulic fluid, e.g., a feed circuit or a steering device.  
         [0012]     In one development of the invention, in the outlet line downstream of the suction line there is a stop valve, such as a check valve, that opens in the delivery direction. It thereby becomes possible for the suction device to produce a vacuum to reduce the housing pressure.  
         [0013]     Preferably, a bypass line is provided, which is in communication with the outlet line, and bypasses the suction device, and which can be used to equalize the pressure if the housing is totally evacuated by the suction device.  
         [0014]     In one preferred embodiment of the invention, the suction device has a pump. A pump is a simple and easy way to generate a vacuum to reduce the pressure inside the housing.  
         [0015]     In one development of the invention, the suction device has a vacuum limiting device. With a vacuum limiting device, an excessive vacuum, which can cause the liquid to foam, can be easily prevented. It thereby becomes possible to guarantee a satisfactory and reliable lubrication of the roller bearings that support the rotor by the fluid.  
         [0016]     The vacuum choke is thereby advantageously realized in the form of a control valve, which is associated with the suction side of the pump, and is pushed toward a closed position by a spring and toward an open position by the housing pressure. With a vacuum choke of this type, the vacuum in the housing produced by the pump can be limited easily and reliably by the adjustment of the spring.  
         [0017]     In an additional preferred embodiment of the invention, the vacuum limiting device is formed by a pressure compensator that is associated with the pump.  
         [0018]     The pressure compensator can be preferably realized in the form of a control valve, which is located in a pump bypass line, and is pushed toward an open position by a spring and toward a closed position by the housing pressure. The vacuum produced by the pump can also be easily and reliably limited by adjusting the spring on a pressure compensator of this type.  
         [0019]     The suction device can be in a drive connection with the machine, as a result of which no separate drive device needs to be provided for the drive of the suction device.  
         [0020]     It is also possible to provide a separate drive motor for the drive of the suction device, such as an electric motor or a hydraulic motor or an internal combustion motor. As a result of which, the suction device can be driven in a simple manner.  
         [0021]     The pump of the suction device can be formed by a separate pump, which is used only for the generation of a vacuum in the housing.  
         [0022]     It is particularly advantageous if a machine incorporating features of the invention is used in a drive system with a booster pump, with the booster pump realized in the form of a pump of the suction device. Consequently, the booster pump of the drive system, which is already present, such as, for example, a feed pump for the supply of a feed circuit or a steering pump for the supply of a steering device, can be used to generate the vacuum in the housing, whereby there is a low construction expense for the machine.  
         [0023]     The pump can be in communication by means of a suction line with a reservoir. As a result of which, it is possible to easily achieve an additional suction-side connection of the booster pump, which is already present, to the reservoir to supply the users that are supplied by the pump with hydraulic fluid.  
         [0024]     In one preferred embodiment of the invention, the machine is realized in the form of an electrical machine, for example in the form of a synchronous or asynchronous machine. As a result of the reduction of the churning losses of the rotor in accordance with the invention, a high output can be achieved with low losses, and, thus, high efficiency, on an electrical machine of the invention.  
         [0025]     In an additional preferred embodiment, the machine can be realized in the form of a hydraulic machine, for example in the form of an axial piston machine, utilizing the swashplate construction with a cylinder drum that forms the rotor. As a result of the reduction of the churning losses of the rotating cylinder drum of the invention, it is thereby possible to operate the axial piston machine at high speeds of rotation and low losses, and thereby with high efficiency.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     Additional advantages and details of the invention are explained in greater detail below on the basis of the exemplary embodiments which are illustrated in the accompanying schematic figures, in which like reference numbers identify like parts throughout.  
         [0027]      FIG. 1  shows a machine of the invention in a schematic illustration;  
         [0028]      FIG. 2   a  shows a first embodiment of a suction device;  
         [0029]      FIG. 2   b  shows a second embodiment of a suction device; and  
         [0030]      FIG. 2   c  shows an additional embodiment of a suction device. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]      FIG. 1  shows a machine  1  of the invention in the form of an electrical machine or a hydraulic machine, having a rotor  3  which is located so that it can rotate in a housing  2 . The interior of the housing  2  is at least partly and preferably completely filled with fluid, for example with coolant in the form of hydraulic fluid. The interior of the housing  2  is connected to an outlet line  5  which runs to a reservoir  6 .  
         [0032]     The section of the outlet line  5  that is in communication with the interior of the housing  2  is connected to the suction side of a suction device  7 . The section of the outlet line  5  that is connected to the pressure side of the suction device  7  leads to the reservoir  6 . In the outlet line  5 , downstream of the suction device  7 , there is a stop valve  8 , which can be realized in the form of a check valve that opens toward the reservoir  6 . Downstream of the stop valve  8 , in the outlet line  5 , are a cooler device  9  and a filter device  10 .  
         [0033]     To bypass the suction device  7 , a bypass line  5   a  is connected to the outlet line  5 .  
         [0034]      FIG. 2   a  shows a first embodiment of a suction device  7 . The suction device  7  has a pump  11  which is connected on the suction side to the section of the outlet line  5  that is connected with the housing  2 , and with the pressure side emptying into the section of the outlet line  5  that leads to the reservoir  6 .  
         [0035]     The suction device  7  has a vacuum limiting device  12 , which is formed by a vacuum choke  13  that is associated with the pump  11 . The vacuum choke  13  is formed by a control valve that acts as a choke in intermediate positions, is associated with the suction side of the pump  11 , and is pushed toward a closed position  13   a  by a spring  14  and toward an open position  13   b  by the housing pressure that is present in the outlet line  5 . For this purpose, a control pressure line  15  is provided which runs from the section of the outlet line  5  that is in connection with the housing to a control surface of the vacuum choke  13  that acts toward the open position  13   b.    
         [0036]     In the embodiment illustrated in  FIG. 2   b,  the vacuum limiting device  12  is formed by a pressure compensator  16  that is associated with the pump  11 . The pressure compensator  16  is realized in the form of a control valve that acts as a choke in intermediate positions, and is located in a pump bypass line  17  that is connected to the outlet line  5 . The pressure compensator  16  that is realized in the form of a control valve is pushed toward an open position  16   a  by a spring  19  and toward a closed position  16   b  by the housing pressure. For this purpose, a control surface of the pressure compensator  16  that acts toward the closed position  16   b  is connected to a control pressure line  18 , which is connected to the section of the pump bypass line  17 , and which is in communication with the section of the outlet line  5  that is in communication with the housing  2 .  
         [0037]     The pump  11 , as illustrated in  FIGS. 2   a  and  2   b,  is realized in the form of a separate pump, which is provided exclusively for the production of a vacuum in the interior of the housing  2  of the machine  1 .  
         [0038]     In the embodiment illustrated in  FIG. 2   c,  the pump  11  is formed by a booster pump which is already present, for example a feed pump for the supply of a feed circuit or of a steering pump for the supply of a steering system or a hydraulic pump for the supply of additional users, for example of a hydraulic system, for the operation of a mobile industrial truck. The section of the outlet line  5  that is connected to the pressure side of the suction device  7  is realized in the form of the delivery line of the pump  11 . For the connection of the pump  11  with the reservoir  6 , the suction side of the pump  11  is connected to a suction line  20 , which is in communication with the reservoir  6 . The suction line  20  is connected with the section of the outlet line  5  that leads to the suction side of the pump  11  downstream of the vacuum limiting device  12 .  
         [0039]     The pump  11  can be associated with a vacuum limiting device  12  as illustrated in  FIG. 2   a.  It is also possible to provide a vacuum limiting device  12  as illustrated in  FIG. 2   b.    
         [0040]     The pump  11  of the suction device  7  can be in a drive connection with the machine  1 . It is also possible to provide a separate driver motor, such as an electric motor for example, a hydraulic motor, or an internal combustion motor.  
         [0041]     The machine can be an electrical machine, e.g., in the form of a synchronous or asynchronous machine, or in the form of a hydraulic machine, for example in the form of an axial piston machine that utilizes a swashplate construction, whereby the cylinder drum forms the rotor.  
         [0042]     It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.