Abstract:
Ejector with driver gas comprising at least one primary nozzle branch ( 12 ) with a driver nozzle ( 36 ) having a cross-sectional narrowing and an adjacent receiving nozzle ( 32 ), wherein a suction line ( 24 ) terminates in the narrowing, characterized by at least one connectable secondary nozzle branch ( 14 ) having a driver nozzle ( 38 ) with a cross-sectional narrowing and an adjacent receiving nozzle ( 34 ), wherein the narrowing of the secondary nozzle branch ( 14 ) is connected to a suction line ( 24 ) when the secondary nozzle branch ( 14 ) is opened, and with a closing instrument ( 20 ) connected upstream, with respect to the flow direction of the gas propellant, of the at least one secondary nozzle branch ( 14 ) to connect and disconnect the secondary nozzle branch ( 14 ) in dependence on the inlet pressure of the driver gas entering the ejector ( 20 ).

Description:
[0001]    This application claims Paris Convention priority of DE 102 50 532.2 filed Oct. 29, 2002 the complete disclosure of which is hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    The invention concerns a gas driven ejector, i.e. a jet pump, for generating underpressure, with at least one primary nozzle branch having a driver nozzle with a cross-sectional narrowing, an adjacent receiving nozzle, and a suction line connected to the narrowing.  
           [0003]    Conventional ejectors or jet pumps of this type function according to the Venturi principle. The filtered and lubricant-free compressed gas flows via a connecting sleeve and a pressuring gas feed line into the ejector and reaches the driver nozzle where the flow velocity of the compressed air serving as the driver gas is increased to supersonic speed in the narrowing. After exiting the driver nozzle, the air expands and flows into a diffuser and from there, optionally via a sound absorber, to the outside thereby producing a vacuum in a chamber surrounding the driver nozzle with air being pumped via a suction line feeding into the chamber. The pumped air and the driver gas introduced into the ejector both exit the ejector via the expansion section.  
           [0004]    With respect to other vacuum pumps, these jet vacuum pumps advantageously have no rotating parts and maintenance and wear are therefore minimum. Moreover, they cannot explode since they function purely pneumatically. In addition, their construction is simple and they can be installed at any location. They do not generate heat and can be connected and disconnected at any time to save energy. Moreover, the vacuum can be generated quickly using short lines between e.g. a suction gripper and the ejector. The compact construction, the low weight and the ability to combine several functions in one device play an important economic role in the field of construction, work preparation, purchasing, mechanical processing, assembly, putting into operation and spare part supply.  
           [0005]    In view of the above, it is the underlying purpose of the invention to provide a gas propulsion ejector which ensures good suction performance in a straightforward manner with low driver gas consumption.  
         SUMMARY OF THE INVENTION  
         [0006]    This object is achieved in accordance with the invention in that at least one connectable secondary nozzle branch is provided which has a driver nozzle with a narrowing and an adjacent receiving nozzle, wherein the narrowing of the secondary nozzle branch is connected to a suction line when the nozzle branch is connected, with a closing instrument being disposed upstream of the at least one secondary nozzle branch to connect/disconnect the secondary nozzle branch in dependence on the input pressure of the driver gas in the ejector.  
           [0007]    In accordance with an embodiment of the invention, the second nozzle branch, e.g. the secondary nozzle branch, is only connected when the inlet pressure is high. The second Venturi nozzle is then activated to provide a very high suction capacity and associated high vacuum. In this case, both Venturi nozzle suction capacities are combined to evacuate e.g. the feed line to a suction gripper. Since the second Venturi nozzle is connected only when required, no driver gas is wasted. In this fashion, the modular connection of one or more additional Venturi nozzles individually adjusts the suction performance while providing sufficient flow velocity at high as well as low required suction performance to always ensure safe operation of the evacuation process.  
           [0008]    Alternatively, the secondary nozzle branch may be connected when the inlet pressure is below a certain switching pressure. In this case, both nozzle branches are used only when the inlet pressures are low and evacuation takes place only via one nozzle branch, i.e. the primary nozzle branch when the inlet pressure is high.  
           [0009]    In accordance with an embodiment, the closing instrument may be held in a first position via a preloading force which counteracts the inlet pressure of the driver gas. The closing instrument may e.g. be a bistable 2/2 way valve. In this case, the preloading force is provided by a spring which acts e.g. on a piston. Depending on whether the secondary nozzle branch is to be connected at low or high working pressures, the first position is defined as the open or closed position. The stop valve or closing instrument is adapted to the desired switching direction. When the switching pressure is reached, the inlet pressure can switch the closing instrument into a second position with that second position being either that state of the closing instrument with which the secondary branch contributes to the suction performance or that state in which it is disconnected, in dependence on the desired switching direction.  
           [0010]    The two nozzle branches may also have a common feed line which contains the closing instrument. In most cases, the driver gas is pressurized air.  
           [0011]    According to a further embodiment, the primary and the secondary nozzle branch may have a common suction line which may, in particular, be a continuous suction line which communicates with the two nozzle branches. A check valve may be disposed in the suction line between the secondary and primary nozzle branch to prevent leaking of the vacuum generated by the first nozzle branch when the secondary nozzle branch is disconnected. When an underpressure is also generated in the secondary nozzle branch, the check valve opens and the underpressure of the secondary nozzle branch also contributes to the suction performance in the suction line.  
           [0012]    Alternatively, at least the secondary nozzle branch, a further nozzle branch, or a group of nozzle branches may each have its own separate suction line. Towards this end, several suction circuits may be connected or disconnected independently of each other.  
           [0013]    The check valve may preferably be a spring-loaded ball valve. The spring forces may be adjusted such that even a small force is sufficient to overcome the spring. In this case, the check valve may already lift off during low suction performance of the secondary nozzle branch. The low spring force is sufficient, since the stop ball is additionally pressed against the closure seat by the underpressure generated when the first nozzle branch is operated to thereby safely prevent leakage. If the spring has a low spring constant, two nozzle branches of equal suction performance may also be operated, since, in this case, the closing element is in a bistable state and the suction line is opened for the second nozzle branch.  
           [0014]    The secondary nozzle branch may have the same or a different suction performance than the primary nozzle branch and preferably a higher suction performance, since this ensures complete and simple opening of the check valve. By providing different Venturi nozzles of different types or performance classes, the suction performance effected in the suction line and exhaust connection may be varied to permit reliable adjustment of the required underpressure and evacuation time.  
           [0015]    In addition to the above-described two nozzle branches, several primary and secondary nozzle branches, which are connected in parallel, may also be provided, with all primary nozzle branches being connected at the same time and all secondary nozzle branches being connected or disconnected at a common switching pressure. In addition to the secondary nozzle branch, a tertiary or quaternary nozzle branch may be provided which is disconnected or connected at a further switching pressure other than the first switching pressure, to further improve the regulation and control of the suction performance in accordance with the requirements.  
           [0016]    All nozzle branches may be connected to one single suction line, preferably in that the nozzle branches intersect that suction line.  
           [0017]    The check valves may be preferably provided only between branches of different connection pressures. In this manner, no check valves are provided between different primary nozzle branches and only one check valve is provided between a group of primary nozzle branches and a group of secondary nozzle branches. If, in addition to primary and secondary nozzle branches, tertiary nozzle branches are also provided, a check valve may be disposed between the primary and the secondary and tertiary nozzle branches.  
           [0018]    All components and nozzle branches of the ejector can thereby be disposed within a common housing. The housing may consist e.g. of a material block into which all lines are introduced as bores with the nozzles and valves being inserted into the block and fixed therein with remaining openings being closed by caps. This provides particular advantages for maintenance, configuration, and replacement of individual components.  
           [0019]    Further advantages and features of the invention can be extracted from the disclosure. The drawing gives a detailed description of a particularly preferred embodiment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0020]    [0020]FIG. 1 shows a diagram of connections of an inventive ejector;  
         [0021]    [0021]FIG. 2 shows an exploded view of an inventive ejector; and  
         [0022]    [0022]FIG. 3 shows a section through an inventive ejector. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]    [0023]FIG. 1 shows a circuit diagram of an ejector or jet pump, designated in its entirety with  10 . The ejector  10  has a primary nozzle branch  12  and a secondary nozzle branch  14 . The two nozzle branches are connected to a feed line  16  for a driver gas, wherein in FIG. 1, a common air supply branch  16  branches into the air supply branches  16 ′ and  16 ″ for the primary nozzle branch  12  and the secondary nozzle branch  14 , respectively. The air supply branch  16 ′ for the primary nozzle branch supplies driver gas to a first Venturi arrangement  18  of the first supply branch  12 . A switching valve  20  is disposed in the second air supply branch  16 ″ to pass air to the second Venturi arrangement  22  of the second nozzle branch  14  or to close off the air supply line  16 ″ of the second arrangement  22 .  
         [0024]    The valve  20  is a bistable 2/2 way valve and is explained in more detail below.  
         [0025]    The primary nozzle branch  12  and the secondary nozzle branch  14  are connected to a suction line  24 . One single suction line  24  connects to the two nozzle branches  12 ,  14  in the region of their respective cross-sectional narrowings of the Venturi arrangements  18 ,  22 . A further line, e.g. for a suction gripper, may be evacuated via the suction line  24  which feeds to a suction nozzle  26 . A check valve  28  (a spring-loaded ball valve) is disposed in the suction line  24  between the primary nozzle branch  12  and the secondary nozzle branch  14  to prevent leakage of the vacuum of the first nozzle branch  12  in the event that the secondary nozzle branch is not connected.  
         [0026]    In the circuit of FIG. 1, the ejector  10  is operated only with respect to the primary nozzle branch  12  as soon as it is loaded with driver gas (compressed air). The valve  20  is thereby held in the blocking position. Acceleration of the compressed air to supersonic speed in the primary nozzle branch  12  generates an underpressure in the region of its cross-sectional narrowing in a chamber surrounding the narrowing, through which the suction line  24  is evacuated. The check valve  28  prevents leakage of vacuum in the chamber.  
         [0027]    As soon as the supply pressure in the feed line  16  of the compressed air reaches a predetermined switching pressure for the valve  20 , the second, i.e. secondary nozzle branch  14  is opened. At this moment, the air consumption is doubled, as is the suction volume.  
         [0028]    As soon as the inlet pressure is reduced, the valve  20  switches back to the blocked position.  
         [0029]    A certain switching hysteresis of the valve  20  must thereby be taken into account.  
         [0030]    The switching pressure is thereby predetermined by the valve  20 .  
         [0031]    The structure is explained below using an exploded view of an inventive ejector  10 . The ejector  10  is mounted in a housing  29  and can be fixed through the housing  29  to a base e.g. via mounting locations  30 .  
         [0032]    The two nozzle branches  12  and  14  thereby consist essentially of a receiver nozzle  32  or  34  and a driver nozzle  36  or  38 , which are connected to each other via an O-ring  40  and form the Venturi arrangements  18 ,  22 . The cross-sectional narrowing in the driver nozzle  36  or  38  accelerates the compressed air introduced into the feed line  16  to supersonic speed.  
         [0033]    A check valve  28  comprising a ball  42  as the closing body and a spring  44  with a low spring constant is disposed between the two nozzle branches  12  and  14  in the suction line  24  which connects the two nozzle branches  12  and  14  and which feeds to a suction nozzle  26 . The vacuum generated in the primary nozzle branch  12  is thereby protected from leakage with respect to the secondary nozzle branch.  
         [0034]    The suction line  24  is closed on both sides of the housing  29  through which it penetrates using cover flaps  46 , in particular plastic lids.  
         [0035]    In a particularly simple fashion, the housing  29  is not merely a cover for the individual parts but a material block into which the individual recesses for the feed line etc. such as e.g. the suction line and the compressed air lines of the nozzle branches  12 ,  14 , which intersect the suction line, are machined, wherein only components such as the driver nozzle, the receiving nozzle, and the valves are separate and are inserted into and fixed in the housing block. In this fashion, replacement of the individual component or insert is particularly easy. A jet pump  10  of this type can be easily adjusted to different types or performance classes without having to replace the entire jet pump  10 . For cleaning and/or inspection, the individual nozzles  32 - 38  can be easily removed, cleaned or examined and be subsequently re-installed. Faulty individual parts may be particularly easy to replace.  
         [0036]    A 2/2 way valve  20  may be provided in the region of the feed line which comprises a piston  48  which forms a unit together with a piston seal  50  and an O-ring seal  52 . The piston is pressed by a spring  54  in the direction of its longitudinal axis, whose spring constant and bias permits adjustment of the switching point. The O-ring  52  thereby seals the compressed air line of the secondary nozzle branch  14  when the piston  48  is in a closed position, i.e. in its first or resting position.  
         [0037]    The side of the spring  54  facing away from the piston  48  abuts a plug  56  via which the spring bias can be adjusted.  
         [0038]    When the valve  20  is closed, compressed air for the primary nozzle branch  12  can flow unhindered past the switching piston  48 . The switching piston has different cross-sections along its length, with the pressure of the flowing compressed air acting on the piston  48 , via an annular surface of larger cross-section formed at a front side of the piston  48  in the region of the larger cross-section to oppose the loading direction of the spring  54 . The compressive forces of the pressurized air thereby depend on the circular area  51  of the piston  48  at which those forces act as well as on the absolute pressure.  
         [0039]    The smaller cross-sectional surface of the piston  48  which corresponds to a corresponding smaller bore in the housing  28  is thereby disposed in the direction of the second  14  nozzle branch.  
         [0040]    If there is compressed air in the feed line  16 , the piston  48  is loaded with pressure at its surface  51 . This force acts against the bias of the spring  54 . As the pressure is increased and as soon as the force exerted by the compressed air exceeds the spring force, the piston  48  is moved against the spring force in the direction of the plug and up to a predetermined stop. The feed line to the secondary nozzle branch  14  is thereby opened and the secondary nozzle branch contributes to the suction performance. This doubles the air consumption and the suction volume.  
         [0041]    If the supply pressure on the inlet line  16  is reduced, the piston  48  moves back towards the second nozzle branch  14  until the O-ring  52  of the piston seal  50 , piston  48  and O-ring  52  assembly abuts the corresponding bore  53  and the associated surface in the housing block  29  to seal the piston  48  in the position on the conical surface  53 .  
         [0042]    [0042]FIG. 3 shows the ejector  10  of FIG. 2 in an assembled state illustrating the position of the check valve between the nozzle branches  12  and  14 .  
         [0043]    The pressure forces of the compressed air thereby act on the annular surface  51 . The spring force of the spring  54  opposes these pressure forces produced by compressed air. If the pressure forces exceed a switching pressure, the piston  48  is pressed downwards (in the illustration) against the spring  54  and permits passage of compressed air to the second nozzle branch  14 .  
         [0044]    As soon as the second nozzle branch also produces a vacuum, the ball  42  of the check valve is moved against the spring force of the spring  44  by the vacuum in the second nozzle branch  14  and towards the second nozzle branch  14  to open the passage in the suction line  24 , wherein additional vacuum is generated on the suction nozzle  26 , e.g. for a suction gripper. The suction performance of the secondary nozzle branch  14  must be greater than or equal to that of the primary branch  12  in order to hold the check valve  28  in the open position.  
         [0045]    As soon as the pressure in the feed line  16  decreases, and the piston  48  closes the feed line to the second nozzle branch  14 , the ball  42  is pressed back into its valve seat by the force of the spring  44  to close the suction line  24  in the region of the narrowing of the first nozzle branch  12 , thereby preventing leakage.  
         [0046]    In this fashion, a second nozzle branch  14  can be connected only when increased suction performance is required and in all other cases, air consumption can be reduced. The air consumption and suction performance can thereby be efficiently controlled.