Abstract:
The invention proposes a method of operating a rotary compressor ( 1 ) with twisted rotors ( 10, 20 ) for compressing gaseous media, in which a gas-dynamic pulse is generated in the delivery chamber ( 4 ) flowed through in each case from an inflow side ( 4 ′) to an outlet side ( 4 ″) in the longitudinal direction of the delivery chamber by rapid separation from an area of enlarged volume (V), and a closing time (t S ) from separation of the relevant delivery chamber ( 4 ) flowed through in the longitudinal direction of the delivery chamber from the area of enlarged volume (V) to closure of the relevant delivery chamber ( 4 ) on the inflow side ( 4 ′) is such that the filling level of the delivery chamber ( 4 ) is increased by pulse charging.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a rotary compressor for compressing gaseous media, having two twisted rotors surrounded by a housing, each with at least three vanes or splines for forming a number of delivery chambers between the vanes or splines and the internal wall of the housing, and a method of operating such a rotary compressor.  
       Prior Art  
       [0002]     Rotary or roots compressors of the above-mentioned type have long been known and are disclosed for example in DE 34 14 039 C2 or DE 31 14 064 C2. As a result of increased requirements, rotary compressors are currently operated at high speeds, whereby the gas mass flow rate is increased accordingly. The increased speeds have as a consequence, however, that only a short time is inevitably available for each individual suction operation. This has the disadvantageous effect of poorer filling (lower charging efficiency) and thus a reduction in the gas mass delivered per revolution. The increase in the mass flow rate of the compressible gaseous or fluid medium is thus less than the increase in speed. The result is limited or declining volumetric efficiency.  
       SUMMARY OF THE INVENTION  
       [0003]     It is therefore the object of the present invention to provide a rotary compressor of the above-mentioned type and a method of operating a rotary compressor which enable increased charging efficiency.  
         [0004]     This object is achieved according to the invention by a method having the features of claim  1  and by a rotary compressor having the features of claim  5 . Advantageous further developments of the invention are indicated in the dependent claims.  
         [0005]     The concept behind the present invention is to increase the charging efficiency of the rotary compressor by generating in the respective delivery chamber a fluid-dynamic pulse in the fluid to be compressed and making purposeful use thereof. In this way, the filling level in the respective delivery chamber is markedly increased and thus very good charging efficiency is achieved even at relatively high speeds. To achieve a pressure pulse in known rotary compressors frequently requires only slight structural and/or operational adaptations or alterations, such that the principles of the present invention may be economically implemented.  
         [0006]     A pressure pulse is generated according to the invention by flow through a delivery chamber with a speed component in the longitudinal direction of the delivery chamber and rapid separation of the relevant delivery chamber from the area of enlarged volume. For efficient utilisation of the fluid-dynamic pulse generated thereby, provision is made according to the invention for the inflow side of the relevant delivery chamber initially still to be open to the suction area and only to be closed at a suitable time, but before a connection is formed between the relevant delivery chamber and the delivery side, in such a way that the filling level of the delivery chamber is increased by pulse charging.  
         [0007]     In other words, with the method and apparatus according to the invention a closing time from separation of the relevant delivery chamber flowed through in the longitudinal direction of the delivery chamber from the area of enlarged volume to closure of the relevant delivery chamber relative to the inflow side is such that the filling level of the delivery chamber is increased by pulse charging.  
         [0008]     The advantages achieved with the invention consist in particular in the fact that an improved charging efficiency and a correspondingly increased volumetric efficiency are achieved by the purposeful generation and utilisation of a gas-dynamic pulse. In this way, the speed range of rotary compressors is markedly increased, since high speeds may also be put to efficient use, which increases overall throughput and improves economic viability.  
         [0009]     The term “gas-dynamic pulse” denotes a phenomenon as also occurs upstream of a valve for example in pipelines in the event of sudden closure of the valve. This results in a pressure front which moves upstream through the medium approximately at the speed of sound. This dynamic process adds a further component to the static pressure in the medium, such that the pressure and, in the case of compressible media, the filling level increase.  
         [0010]     According to a further development of the method according to the invention, operation of the rotary compressor is controlled by varying geometric influencing variables and/or the speed of the rotary compressor, taking account of the temperature and type of the gaseous medium. The temperature and type of the gaseous medium determine the propagation of a gas-dynamic pulse within the medium and are therefore taken specifically into account according to the invention when operating the rotary compressor. The speed of the rotary compressor has a direct effect on the closing time and the separation time, which has still to be discussed below, and is therefore an important parameter when operating a rotary compressor in accordance with the invention. The individual geometric variables will be examined in more detail below.  
         [0011]     To ensure effective generation of a gas-dynamic pulse, provision is made according to a further development of the present invention for the rapid separation to take place within a separation time, in which the rotors each pass through a rotation angle of the size of the angle of twist and which is less than twice the transit time of the gas-dynamic pulse for passage through the relevant delivery chamber in the longitudinal direction of the delivery chamber. It may generally be noted that, as the separation time is progressively reduced, the gas-dynamic pulse becomes ever more pronounced. Therefore, with regard to the desired improvement in charging efficiency, in preferred embodiments the separation time should be limited stepwise to 1.5 times, 1.0 times, 0.75 times and 0.5 times.  
         [0012]     In addition to effective generation of a pressure pulse, it is however also important according to the invention for the pressure pulse also to be utilised efficiently for increased filling of the relevant delivery chamber, so raising the charging efficiency. To this end, according to a further development of the present invention provision is made for the closing time to be less than 1.75 times the transit time. In this way it is ensured that the pressure pulse generated in the delivery chamber does not “fizzle out”, wherein optimum exploitation of the pressure pulse is achieved if the closing time corresponds approximately to the transit time. Accordingly, it is particularly preferable for the ratio between closing time (t S ) and transit time (t L ) to be as close as possible to a ratio of 1.0 and to lie in the following ranges: 
        0.25&lt;t S /t L &lt;1.75;     preferably 0.50&lt;t S /t L &lt;1.50;     particularly preferably 0.75&lt;t S /t L &lt;1.25.        
 
         [0016]     In the case of the rotary compressor according to the present invention generally defined in claim  5 , an inflow opening is preferably provided which allows inflow at least in phases, in the longitudinal direction of the delivery chamber. The starting point for this preferred embodiment is the fact that the pressure pulse generated in the relevant delivery chamber produces a suction action. This suction action is used according to the invention to increase filling of the relevant delivery chamber, wherein the medium necessary to increase filling enters the relevant delivery chamber via the inflow opening.  
         [0017]     According to a further development of the invention, the inflow opening is defined at least in places by a control edge, the shape of which preferably approaches that of a vane or spline portion which passes in front of the control edge when the rotary compressor is in operation. Through this measure, the inflow of medium into the relevant delivery chamber may be controlled exactly both time-wise and with regard to amount, such that the filling level may be increased and “fizzling out” of the pressure pulse may be prevented. The shape of the control edge does not have to correspond exactly to that of the vane or spline portion, but rather may also be flattened out and approach a linear shape.  
         [0018]     With regard to maximally variable operation of the rotary compressor, it is also particularly preferred for the inflow opening to exhibit an adjustable geometry, and in particular for the control edge to be adjustable. This measure makes it possible, for example, to adapt the inflow ratios at the inflow opening to the operating speed of the rotary compressor, the temperature or type of medium to be delivered etc., in order thus to ensure that the rotary compressor is efficient and economically viable over a wide range of speeds.  
         [0019]     The above-mentioned geometric influencing variables relate in general to the configuration of the components of the rotary compressor according to the invention. According to the invention, however, it is particularly preferable for the geometric influencing variables to comprise at least one or more of the following variables: 
        length of respective delivery chamber ( 4 ) in longitudinal direction of delivery chamber,     construction and/or arrangement of inflow opening into respective delivery chamber ( 4 ),     angle of twist (β) of rotors ( 10 ,  20 ),     number (n) of vanes or splines ( 12 ,  14 ,  16 ,  22 ,  24 ,  26 ) per rotor.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  shows a schematic perspective view of two twisted rotors for a rotary compressor according to the invention;  
         [0025]      FIG. 2  shows a schematic perspective view of a rotary compressor  1  as preferred embodiment of the present invention;  
         [0026]     FIGS.  3  to  6  each show a schematic sectional view of the rotary compressor  1  illustrated in  FIG. 2  in various operating phases, wherein the section is taken along the edge of the rotors  10  and  20  facing the observer in  FIG. 2 ;  
         [0027]      FIG. 7  shows a schematic sectional view of a modified embodiment of the rotary compressor  1  in the operating phase corresponding to  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0028]     Preferred embodiments of the invention will be described in detail below with reference to the accompanying drawings.  
         [0029]      FIG. 1  shows a schematic perspective view of two twisted rotors  10 ,  20  for a rotary compressor according to the present invention. The rotors  10 ,  20  are each provided in the present embodiment with three vanes or splines  12 ,  14 ,  16 ,  22 ,  24 ,  26  and are arranged so as to mesh together. At their respective ends the rotors  10 ,  20  have shafts  18 ,  28  which are merely hinted at in the Figures, these being used to mount and drive the rotors rotatably in a housing or the like. The rotors  10 ,  20  are twisted about their longitudinal axes, wherein the degree of twist may be stated as an angle β, which indicates the angle of twist between the respective ends of the rotors  10 ,  20 . The angle of twist β amounts in the present embodiment to 40°, although the present invention is not restricted thereto. Indeed, the angle of twist β may in principle assume any desired value, provided it is not so large that a by-pass arises between delivery side and suction side.  
         [0030]      FIG. 2  shows a schematic perspective view of a rotary compressor  1  as preferred embodiment of the present invention. The rotary compressor  1  illustrated in  FIG. 2  comprises the twisted rotors  10 ,  20  already described with reference to  FIG. 1 , which are surrounded by a housing  2  and mounted rotatably therein via the shafts  18 ,  28 . Between the vanes or splines  12 ,  14 ,  16 ,  22 ,  24 ,  26  of the rotors  10 ,  20  and an internal wall  2 ′ of the housing  2  there are formed delivery chambers  4 , through which a medium to be delivered flows during operation of the rotary compressor. It should be noted in this respect that, during operation of the rotary compressor delivery chambers are continuously being formed and dissolved by the two rotors  10 ,  20 ; however only one delivery chamber  4  is discussed below by way of example. In addition, an area of enlarged volume V is formed in the area between the rotors  10 ,  20 , i.e. an area in which the volume between adjacent vanes is enlarged on rotation of the rotors  10 ,  20  and in this way delivery medium is drawn in.  
         [0031]     The inflow of the delivery medium into the rotary compressor  1  takes place on an inflow side  4 ′ via inflow openings  30 , which are provided in such a way that inflow into the rotary compressor takes place at least partially axially. As is clear from  FIG. 2 , the inflow openings  30  are each defined on one side by a control edge  32 , the shape of which corresponds to that of a vane portion which passes in front of the control edge  32  when the rotary compressor  1  is in operation. Although in the present embodiment a fixed control edge  32  is illustrated, the geometry of the control edge  32  may be adjustable, in particular even during operation of the rotary compressor  1 .  
         [0032]     During operation of the rotary compressor, the delivery medium flows through the respective delivery chamber  4  in the longitudinal direction from an inflow side  4 ′ to an outlet side  4 ″, i.e. from the side facing the observer in  FIG. 2  to the side remote from the observer in  FIG. 2 . For the purpose of clarification, the ends of the vanes or splines located on the inflow side are designated  12 ′,  14 ′,  16 ′,  22 ′,  24 ′,  26 ′, while the ends of the vanes arranged on the opposite side are designated  12 ″,  14 ″,  16 ″,  22 ″,  24 ″,  26 ″ (see also  FIG. 1 ).  
         [0033]     Operation of the rotary compressor  1  according to the invention is described in detail below with reference to FIGS.  3  to  6 , which each show a schematic sectional view of the rotary compressor  1  shown in  FIG. 2  in different operating phases, wherein the section is taken along the edge of the rotors  10  and  20  facing the observer in  FIG. 2 . In the individual views, the outlines of the ends of the rotors  10 ,  12  facing the observer are illustrated with continuous lines, while the outlines of the ends of the rotors  10 ,  20  remote from the observer are illustrated with broken lines.  
         [0034]      FIG. 3  shows “Phase I”, in which delivery medium is drawn into the rotary compressor  1  in the area of enlarged volume V, said medium subsequently being discharged on the delivery side in the area of a discharge opening A. The direction of rotation of the rotors  10 ,  20  is indicated in  FIG. 3  and the subsequent FIGS.  4  to  6  by two arrows, i.e. the rotor  10  rotates anticlockwise while the rotor  20  rotates clockwise.  
         [0035]     The beginning of the next “Phase II” is illustrated schematically in  FIG. 4 . Phase II is initiated in that the delivery chamber  4 , which is formed between the splines  12 ,  14  of the rotor  10  and the internal wall  2 ′ of the housing  2 , is separated from the area of enlarged volume V. This separation takes place in that the rear end  14 ″ of the rotor spline  14  comes to rest against or form a seal with the internal housing wall  2 ′ at the point indicated in  FIG. 4  by a suction-side apex angle f S , so separating the delivery chamber  4  from the area of enlarged volume V. Through the rapid separation of the delivery chamber  4  from the area of enlarged volume V, a gas-dynamic pulse is generated in the delivery chamber  4  at approximately the time illustrated in  FIG. 4 .  
         [0036]     Separation of the delivery chamber  4  from the area of enlarged volume V takes place over a period in which the rotors  10 ,  20  each pass through a rotation angle of the size of the angle of twist β, said period thus decreasing as the speed increases. The separation time may therefore be defined for example as follows for purely axial inflow: 
 
separation time  t   T =angle of twist β/(6*speed  n ). 
 
         [0037]     The gas-dynamic pulse generated in the delivery chamber  4  is then propagated in the delivery chamber  4  from the side remote from the observer to the side facing the observer (inflow side), approximately at the speed of sound, which is in turn dependent on the temperature and properties of the delivery medium. A transit time t L , which the gas-dynamic pulse requires to pass through the delivery chamber  4  in the longitudinal direction of the delivery chamber, is accordingly: 
 
transit time  t   L =length of delivery chamber 1/speed of sound  a  
 
         [0038]     As Phase II continues, the delivery chamber  4  continues to be connected with the inflow side via the inflow opening  30  (see also  FIG. 2 ), such that delivery medium continues to enter the delivery chamber  4  under the action of the gas-dynamic pulse and the filling level of the delivery chamber  4  is increased continuously.  
         [0039]     With closure of the delivery chamber  4  on the inflow side, the beginning of “Phase III” is reached, which is illustrated schematically in  FIG. 5 . At this point, the inflow-side end  14 ′ of the vane  14  has moved so far past the control edge  32  that the inflow opening  30  is completely closed. The delivery chamber is now completely closed and is conveyed on together with the admitted delivery medium in the direction of rotation, in order to discharge the delivery medium at the discharge opening A. The period of time required from separation of the delivery chamber  4  from the area of enlarged volume V to complete closure of the delivery chamber  4  depends on the closing angle α S  indicated in  FIG. 4  and the speed n and is calculated as follows: 
 
closing time  t   S =closing angle α S /6*speed  n  
 
         [0040]     In “Phase IV” the delivery medium contained in the delivery chamber  4  is finally discharged on the delivery side at the discharge opening A. Phase IV is initiated in that the inflow-side end section  14 ′ of the spline  14  sweeps the line of the delivery-side apex angle f D , such that the delivery chamber  4  in question is connected with the delivery side and the discharge opening A. A position of the rotary compressor during Phase IV is illustrated schematically in  FIG. 6 . In this position, the delivery chamber  4  is connected with the discharge opening A and the delivery medium is discharged continuously through the progressive rotation of the rotors  10 ,  20 . At the same time, of course, similar operations to those described above are taking place in the other delivery chambers.  
         [0041]     The geometry and operating parameters of the rotary compressor  1  according to the invention are such that the above-described gas-dynamic pulse is effectively generated and then utilised to increase the filling level of the respective delivery chamber. To this end, rapid separation of the delivery chamber  4  in question takes place within a separation time t T , which is less than twice the transit time t L  and amounts for example to 1.50 times the transit time t L . Furthermore, the separation time t T  and the transit time t L  are also adjusted to one another in such a way that they lie in the following preferred ranges: 
        0.25&lt;t S /t L &lt;1.75;     preferably 0.50&lt;t S /t L &lt;1.5     particularly preferably 0.75&lt;t S /t L &lt;1.25        
 
         [0045]     As is obvious from the above explanations, the geometric influencing variables, which influence the operating characteristics of the rotary compressor according to the invention, comprise the following variables: 
        length of respective delivery chamber ( 4 ) in longitudinal direction of delivery chamber,     construction and/or arrangement of inflow opening into respective delivery chamber ( 4 ),     angle of twist (β) of rotors ( 10 ,  20 ),     number (n) of vanes or splines ( 12 ,  14 ,  16 ,  22 ,  24 ,  26 ) per rotor.        
 
         [0050]     A schematic sectional view of a modified embodiment of the rotary compressor  1  is shown in  FIG. 7 , in an operating phase corresponding to  FIG. 4 . The embodiment shown in  FIG. 7  differs from the previous embodiment in that the control edge  32  has an outline whose shape approaches that of a vane portion which passes in front of the control edge  32  when the rotary compressor is in operation. As a result of this configuration, the inflow of medium into the respective delivery chamber  4  may be effectively controlled in that large amounts of medium continue to flow into the delivery chamber  4  until the end of the closing time t S , while, at the end of the closing time t S , the delivery chamber  4  is separated as rapidly as possible, in order in this way particularly effectively to prevent “fizzling out” of the gas-dynamic pulse generated in the delivery chamber  4  and to achieve the best possible filling of the delivery chamber  4 . The control edge  32  may also assume a somewhat flatter form, as shown in  FIG. 7 , and may in a preferred embodiment also be adjustable as a function of the operating parameters of the rotary compressor  1 , for example as a function of the operating speed etc.