Abstract:
A flowmeter for liquids has a measuring housing, which encloses and rotatably mounts an impeller, said measuring housing comprising a one-piece supply pipe and discharge pipe, wherein the impeller is eccentrically arranged in the discharge pipe after a nozzle-forming constriction. A sensor encoder is associated with the impeller and a sensor which responds to the sensor encoder is provided on the measuring housing for determining the amount of liquid flowing through the measuring housing on the basis of the revolutions of the impeller. The outer diameter corresponding to the impeller is smaller than the nominal inner diameter of the discharge pipe, enabling it to be pushed into the one-piece pipe.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a flowmeter for liquids, having a measuring housing which encloses and rotatably mounts an impeller, a supply pipe, a discharge pipe, at least one sensor encoder which is assigned to the impeller, and a sensor which is provided on the measuring housing and responds to the sensor encoder and has the purpose of determining the amount of liquid flowing through the measuring housing on the basis of the revolutions of the impeller. 
       PRIOR ART 
       [0002]    A flowmeter having a number of features of the type mentioned at the beginning is known from GB 2,382,661. This patent application uses a sensor for detecting the Hall effect with a corresponding magnet which is assigned to the impeller. In this context, this magnet is, in particular in contrast with older models, removed from the path of the liquid since such an arrangement has, according to the information in this document, a negative influence on the device as such and makes it difficult to replace the magnets. 
         [0003]    In GB 2 382 661 the magnet is arranged outside the course of the liquid. 
         [0004]    In EP 2 166 316, which is based on this British document as prior art, an inflow connector, which is integrally molded onto the measuring housing, is used to enclose therein as an additional element a nozzle pipe which forms a nozzle duct. 
         [0005]    Although the cited documents operate satisfactorily on the basis of the measuring principle of the Hall effect, they are less suitable in their dimensions for applications with very restricted space as a result of the cylindrical measuring housing with an integrally molded-on connector. 
         [0006]    A flowmeter having the features of the type mentioned at the beginning is known from EP 2 154 490. Here, the measuring housing is a pipe which surrounds the supply pipe and the discharge pipe in one piece and in which a nozzle-forming constriction is arranged eccentrically between the supply pipe and the discharge pipe. The impeller is rotatably mounted in the discharge pipe which is widened for the measuring housing, wherein the impeller is approximately twice as big as the diameter of the supply pipe and discharge pipe. A constriction of the one-piece pipe is provided centrally. The disadvantage of this prior art is therefore, inter alia, that the space required for the measuring housing which projects over the outer diameter of the pipe composed of supply pipe and discharge pipe is large and therefore the circular dimension determined by the cross section composed of supply pipe and/or discharge pipe projects out. 
         [0007]    Similar flowmeters are known from WO2011/055362 A1 and FR2 428 827 A1. 
       SUMMARY OF THE INVENTION 
       [0008]    Taking this prior art as a starting point, the invention is based on the object of configuring a flowmeter of the type mentioned at the beginning to be smaller and to be capable of being more easily positioned. In particular, an object of the invention is to specify a space-saving flowmeter which can easily be installed in the lines of a hot beverage or cold beverage preparation device. In this context a further object of the present invention is to connect the necessary electrical and electronic systems as a control unit in a compact fashion and without requiring additional space, for example by clipping on the measuring housing pipe with this control unit. 
         [0009]    A further object of the present invention is to simplify the assembly of the flowmeter and to use fewer parts. 
         [0010]    These objects are achieved according to the invention for a flowmeter of the type mentioned at the beginning having, inter alia, the features of claim  1 , in which the flowmeter for liquids has a measuring housing which encloses and rotatably mounts an impeller, in which the measuring housing itself is composed of a supply pipe and a discharge pipe. In this context, at least one sensor encoder which is assigned to the impeller and a sensor which is provided on the measuring housing and responds to the sensor encoder and has the purpose of determining the amount of liquid flowing through the measuring housing on the basis of the revolutions of the impeller are provided. The measuring housing is a pipe which comprises the supply pipe and the discharge pipe in one piece and in which a nozzle-forming constriction is arranged eccentrically between the supply pipe and the discharge pipe. The impeller is rotatably mounted in the discharge pipe downstream of the nozzle-forming constriction. In this context, the outer diameter corresponding to the impeller is smaller than the nominal inner diameter of the discharge pipe. 
         [0011]    The sensor is advantageously a Hall sensor. 
         [0012]    The impeller advantageously has, in the plan view in the axial pipe direction an outer face in each rotational position, such that the impeller fits into the free space provided by the inner pipe, wherein the impeller has two side walls, on each of which a bearing element is provided axially in the center, said bearing element being assigned to a rotary bearing which is assigned to the discharge pipe. The axis of the rotary bearing is perpendicular to the longitudinal axis of the pipe, and the sensor is advantageously attached perpendicularly with respect to the two specified axes above or below the pipe. 
         [0013]    The bearing is advantageously composed of in each case a bearing cone at the ends of the rotational axis, which bearing cones engage in corresponding openings as a rotary bearing in or in front of the wall of the discharge pipe. 
         [0014]    The flowmeter can be provided with a bearing cage, for which purpose at least two attachment elements, for example guide fins, are provided in the discharge pipe, onto which guide fins the bearing cage for the impeller can be fitted. These elements serve as guide elements or positioning elements and protect the cage against rotation and serve likewise to position it. This bearing cage is advantageously secured in its axial position by means of ratchet pawls. 
         [0015]    The bearing cage can be composed of a ring on which bearing arms which lie opposite one another are integrally formed, said bearing arms protruding essentially at a right angle from the ring. Deviation from the right angle can be dependent, in particular, on the tightening of the injection mold. The bearings can be provided in these bearing arms. The bearing arms are advantageously pushed forward in the direction of the constriction, with the result that the ring is arranged downstream. In principle, the bearing is also possible in the opposite direction, but the first-mentioned solution is preferred. 
         [0016]    The impeller can have three or four blades. The number is basically not restricted; there can therefore be four, six, eight, nine, ten blades or some other number of blades. In this context, the impeller can be an injection molded part, wherein it is composed of a permanently magnetic injection molded plastic, at least in one blade. This can be achieved by means of 2 k injection molding material. The entire impeller can also be formed from the permanently magnetic injection molded plastic since the changes in the magnetic field are determined by the blades which are remote from the axis. 
         [0017]    In another embodiment, the impeller can be an injection molded part, wherein at least one blade has a permanent magnet which is at least partially enclosed by injection molding. 
         [0018]    As a result, the flowmeter is arranged completely in the essentially tubular measuring housing and therefore the measuring housing is a “measuring pipe”, no additional space is required for the connection of the switching unit and the measuring housing pipe in a hot beverage or cold beverage preparation device since said measuring pipe can easily be inserted into a corresponding compatible switching unit which has releasable or non-releasable latching elements, such as a hose or pipe into a pipe clip. 
         [0019]    Further embodiments are given in the dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Preferred embodiments of the invention are described below with reference to the drawings which are merely for the sake of explanation and are not to be interpreted as being restrictive. In the drawings: 
           [0021]      FIG. 1  shows a partially cut-away perspective view of a flowmeter according to an exemplary embodiment of the invention; 
           [0022]      FIG. 2  shows a sectional view of the section in  FIG. 1 ; 
           [0023]      FIG. 3  shows a perspective view of an impeller according to the exemplary embodiment in  FIG. 1 ; 
           [0024]      FIG. 4  shows a perspective view of an alternative impeller for an exemplary embodiment according to  FIG. 1 ; 
           [0025]      FIG. 5  shows a bearing cage for an impeller according to  FIG. 3  or  4  for a flowmeter according to  FIG. 1 ; 
           [0026]      FIG. 6  shows a partially cut-away perspective view of an alternative pipe for a flowmeter according to a further exemplary embodiment of the invention; 
           [0027]      FIG. 7  shows a partially cut-away perspective view of an alternative pipe with an inserted impeller for a flowmeter according to a further exemplary embodiment of the invention; 
           [0028]      FIG. 8  shows a perspective view of the sensor housing of the flowmeter according to  FIG. 1 ; 
           [0029]      FIG. 9  shows a further perspective view of the sensor housing according to  FIG. 8 ; 
           [0030]      FIG. 10  shows a perspective view of the measuring housing of the flowmeter according to  FIG. 1 ; 
           [0031]      FIG. 11  shows a cross section through a measuring housing having a throughflow restrictor inserted into the discharge pipe; 
           [0032]      FIG. 12  shows a perspective view of the throughflow restrictor from  FIG. 11 ; 
           [0033]      FIG. 13  shows a plan view of the throughflow restrictor from  FIG. 11 ; 
           [0034]      FIG. 14  shows a cross section through a measuring housing having a throughflow restrictor fitted onto the discharge pipe; 
           [0035]      FIG. 15  shows a perspective view of the throughflow restrictor from  FIG. 15 ; and 
           [0036]      FIG. 16  shows a plan view of the throughflow restrictor from  FIG. 16 . 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0037]      FIG. 1  shows a partially cut-away perspective view of a flowmeter according to an exemplary embodiment of the invention. A measuring housing  10  is fitted with its discharge pipe  11  into a sensor housing  30 , as will be explained in more detail below. The measuring housing  10  is tubular and is not damaged in any way, which means that it has only two pipe openings  12  and  13 . The supply pipe is denoted by the reference number  12 , and the discharge pipe is denoted by the reference number  13  opposite. 
         [0038]    From the sectional view in  FIG. 2  of the section in  FIG. 1  it can be seen that the discharge pipe  11  has a flange  18 , opposite which an opposing flange  19  is arranged, which opposing flange is fitted in between the outer walls  31  and  32  of the sensor housing. The orientation of the throughflow direction is ensured by the orientation groove  21  on the other side of the opposing flange. The orientation of the pipe  11  in the circumferential direction will be described later in relation to  FIG. 10 . 
         [0039]    The supply pipe  12  and also the discharge pipe  13  have a predetermined inner diameter which is preferably of the same size, for example 4.1 millimeters in the case of an outer diameter of the pipe  11  of 6 millimeters and a length of the same of approximately 3.3 centimeters. Of course, and as already apparent from the approximate data, other sizes are also conceivable depending on the throughflow amount required. The supply pipe  12  constricts to a constriction  14  which acts as a nozzle and which is arranged radially offset with respect to the longitudinal axis of the measuring housing  10 . The longitudinal axis is located in the plane of the drawing in  FIG. 2  at the level of the positioning fin  16  which will be described later. The constriction  14  is reached via two junction faces which have a curve and between which an asymmetrical cone is arranged. The constriction  14  has a diameter which is preferably in the range between 20% and 40% of the nominal diameter of the supply pipe  12 , and in the case of an exemplary embodiment of the type mentioned above this is, for example, 1.33 millimeters. The constriction  14  is arranged in such a way that it does not contain the longitudinal axis of the inner pipe. At the same time, it is provided with a small step  24  (see  FIG. 6  or  7 ) with respect to the rear wall  15  in the region of the discharge pipe  13 , with the result that the direction of the jet impinges on an impeller or turbine  50  which is fitted into the measuring housing  10 . The corresponding impact face  54  is denoted in the perspective view of the impeller  50  in  FIGS. 3 and 4 . This step  24  can also be omitted in other exemplary embodiments which are not shown in the figures. 
         [0040]    In  FIG. 1 , the measuring housing  10  is fitted into a recess  35  in the sensor housing  30 . The sensor housing  30  without the measuring housing  10  is illustrated in greater detail in  FIGS. 8 and 9 ; the measuring housing without the sensor housing  30  is illustrated in greater detail in  FIG. 10 . 
         [0041]    The bearing of the measuring housing  10  in the sensor housing  30  in the axial direction is ensured by the flanges  18  and  19 , which bear against the side walls  31  and  32  of the sensor housing from the outside. From the lower side a tongue  33  is provided in the sensor housing  30 , which tongue engages behind a corresponding fin in the outer pipe  11  and therefore leaves the measuring housing  10  and the sensor housing  30  in two different parts, which ensures the division of the course of the liquid from the sensor  90 . The sensor  90  is a Hall sensor, which is arranged in the radial extension of the axis of the vertical impeller  50 . In the illustrated exemplary embodiment, said sensor  90  is fitted into a corresponding slot  36  in the sensor housing  30  and is preferably sealed with an insulating silicone. For this purpose, a connecting opening  44  is provided on the upper side of the sensor housing  30 , through which connecting opening  44  this insulating material can be injection molded into the cavity which accommodates the sensor  90 . 
         [0042]    The sectional drawing in  FIG. 2  illustrates a positioning fin  16  in the pipe on the discharge side  13 , which positioning fin  16  is provided from almost the end of the discharge pipe  13  as far as the region of the axis of the impeller. In the illustrated exemplary embodiment here there are two fins  16  which are arranged on both sides of the discharge pipe  16  at an angle of 180° with respect to one another. In other exemplary embodiments, there can also be three fins  16  with an angular spacing of 120° or four fins with a spacing of 90°. 
         [0043]    There are then four ratchet pawls  17  associated with the two fins  16 , said ratchet pawls  17  being arranged in pairs at a small angle of 40° with respect to one another. 
         [0044]    The fins  16  are provided to interact with the bearing arm grooves  63  of the bearing cage  60 , which is illustrated in more detail in  FIG. 5 . The bearing cage  60  is fitted into the outer pipe  11  from the discharge pipe side  13  until it comes to rest behind the ratchet pawl  17 . In the exemplary embodiment illustrated here, two ratchet pawls  17  are injection molded in the discharge pipe  13  as a bump and are at an angle of 90° with respect to the positioning fin  16 . In the case of three positioning fins with an angular spacing of 120°, for example three catches  17  can be provided with an angular spacing of 60° with respect to the fins  16 . The positioning fins  16  can also have a bump or form an elevation, which becomes ever smaller, over the inner diameter, with the result that they can also assume the securing function for the cage  60 . 
         [0045]    The exemplary bearing cage  60  which is illustrated in  FIG. 5  has a ring  61  whose outer wall  69  has a diameter which fits into the inner diameter of the discharge pipe  13 . Two bearing arms  62  which lie opposite one another are injection molded in one piece onto the ring  61 , said bearing arms  62  having the abovementioned bearing arm grooves  63  on their outer side and ending in a run-up projection  64  at which there is only the groove  63  and there are no longer any guiding side walls. The bearing arms are of such a length that they advantageously either abut against the end wall of the constriction  14  in the discharge pipe  13  and therefore ensure the axial position of the bearing cage  60  with respect to the catches  17 , or that they abut against a wall which correspondingly protrudes from the constriction  14  as a stop. 
         [0046]    Bearing openings  66  which are lower than the guide grooves  65  leading to them are provided on the inside of the bearing arms  62 , at locations lying opposite one another. These guide grooves  65  permit the impeller  50  to be fitted in by the run-up projection  64 , for example according to  FIG. 3  or  4 . 
         [0047]      FIG. 3  shows a perspective view of an impeller  50  according to the exemplary embodiment in  FIG. 1 . The impeller  50  has four blades  51  which are each configured as a trapezium in the front view. They therefore have an outer face  52  which is adjoined on both sides by an beveled face  53 , with the result that the impeller fits into the free space predefined by the inner pipe. Two side walls  55  are provided laterally, and rising from said side walls in the center is a bearing cone  56  which starts from a widened cone base. The termination of the bearing cone  56  is a rounded cone tip. 
         [0048]    The impeller  50  according to  FIG. 3  therefore has four impact faces  54 . 
         [0049]    In principle it would also be possible to provide a three-bladed impeller  50 . Impellers with two blades have fewer preferred properties as an embodiment. Impellers with four and more blades are further alternative embodiments. 
         [0050]    The impeller  50  according to  FIG. 3  is an injection molded part composed of a magnet embedded in plastic, such as the material HF14/22 from Schrammberg (MS-Schrammberg GmbH &amp; Co. KG in DE-870713 Schrammberg-Sulgen). Another magnetic material which is embedded by injection molding and can be processed using an injection molding method is the Clerablent product from Barloc Plastics GmbH from DE-51766 Engelskirchen, wherein the material comprises ferrite-filled compounds based on a wide variety of different thermoplastics for manufacturing magnetic functional parts. 
         [0051]    In another exemplary embodiment according to  FIG. 4 , an alternative impeller  150  is illustrated. Identical features are characterized in all the figures in each case with the same reference symbols, and similar features are characterized by similar reference symbols. The impeller  150  also has four blades  51  and impact faces  54 , wherein such an impact face has a cast-on depression  153  here. For reasons of symmetry, two cast-on depressions  153  are provided on the faces lying opposite one another on each blade  51 , that is to say twice. 
         [0052]    The bearing cone  56  with its rounded tip is configured in the same way as the exemplary embodiment according to  FIG. 3 ; however, the plastic which is used for the impeller here is a customary non-magnetic injection molded plastic. The magnetic components which are necessary to operate the Hall sensor are implemented by magnets  160 , inserted in the injection molding, in two further blades. These further blades  151  therefore have walls  161  which are enclosed by injection molding laterally around the magnets  160 , while the outer face  152  corresponds in principle to the face  52  of the other blades  51 . 
         [0053]    Both types of impellers  50  or  150  can be inserted into the cage  60  and the latter is subsequently pushed forward behind the catches  17 . 
         [0054]    Instead of the cone  56  and the bearing opening  66 , this bearing can also be implemented in an inverted fashion, in particular when a bearing cage  60  is used, that is to say that the openings are provided in the side walls  55  and the cones are implemented as elevated portions instead of the openings  66  in the side arms  62 . It is also possible to have a raised portion on one side of the turbine and a depression on the other. 
         [0055]    In a further alternative exemplary embodiment according to  FIG. 6 , a partially cut-away perspective view of an alternative pipe  110  for a flowmeter according to a further exemplary embodiment of the invention is illustrated. The sensor housing  30  which has already been described above and is also illustrated in  FIGS. 8 and 9  can be adopted without modification for this pipe  110  as a measuring housing, since the outer pipe  11  can be correspondingly provided with the flanges  18  and  19 . The supply pipe  12  and the discharge pipe  13  with the constriction  14  as a nozzle between them are configured precisely as in the exemplary embodiment of the pipe  10  according to  FIG. 1 . The rear wall  15  of the constriction is also the same. The bearing openings  166  are also provided in the discharge pipe in the longitudinal direction, said bearing openings  166  being therefore located in the outer pipe  11 , without, however, penetrating it. The dimensions of the cone  56  must then be somewhat longer in order to be suitable for direct use. The bearing cone  56  is then inserted with the correct orientation into the guide groove  112  between the guide fins  111 , wherein it is pushed forward without a large amount of play in the direction of the bearing opening  166 . In this context, it runs up onto a ramp  113 , which reliably prevents the impeller  50  from slipping out after the bearing cone  56  slides into the bearing opening  166 . 
         [0056]      FIG. 7  shows a partially cut-away perspective view of an alternative pipe  210  with an inserted impeller  50  for a flowmeter according to a further exemplary embodiment of the invention. This is also a cage-free solution where the bearing openings are let into a guiding elevated portion  211 , which only has a lateral ramp  213  via which the bearing cones  56  are inserted. For a practical configuration it is possible here for a blade  51  of the impeller  50 , here the blade  51  which is oriented in the longitudinal direction of the discharge pipe  13 , to be secured by pincers and fitted into the pipe  13  in the position illustrated in  FIG. 7  if in the process the measuring pipe to be mounted is deformed selectively with an external force. In addition,  FIG. 7  shows clearly that there is a small step  24  on the rear wall  15 , with the result that the main jet direction which is predefined by the constriction  14  impacts centrally on the impact face  54 . In this alternative solution, the cone would also have to be somewhat longer. 
         [0057]      FIGS. 8 and 9  show a perspective view of the sensor housing  30 .  FIG. 8  clearly shows the receptacle  35  with the receptacle rear wall  34 , in which this receptacle rear wall  34  comprises two separate fins which are formed by the end edges of the side walls  31  and  32 . At the same time, the receptacle  35  has an upper and lower boundary, against which boundaries upper sides  22  or the front or rear side  23  of the discharge pipe  11 , which can be seen in  FIG. 10 , abut. As a result of the steps  45  provided on the receptacle rear wall  34 , there results, through interaction with the locking tongue  33 , a pull-off securing means and, if appropriate, a clamping means of the discharge pipe  11  in the sensor housing  30 . 
         [0058]    The equipping of the housing  30 , to be performed from this side, with the Hall sensor  90  is shown by the reference symbol  36 . On the opposite rear side of the sensor housing  30 , the corresponding plug receptacle  37  can be seen, where electrical contact of the line guide with the Hall sensor contacts is then made. The guide fin  43  ensures correct plugging of the plug into the opening  37 . 
         [0059]    The connecting receptacle  38  contains a locking tongue  39  which protrudes beyond the rear side of the sensor housing  30 , in order to mount the plug housing in a device which requires the flowmeter. A further opening is shown by the reference symbol  36 , which opening is a demolding clearance region for the locking tongue  33  in the injection molding process. 
         [0060]    Finally,  FIG. 10  shows a perspective view of the measuring housing  10  of the flowmeter according to  FIG. 1 . It is to be noted here that the opposing flanges  19  are two non-circular flanges, such as the flange  18 , and that the orientation groove  21  is additionally provided with a bridge  25  in order to ensure the correction installation of the measuring housing in the sensor housing  30 . In order therefore to detect the position of the measuring pipe  10  in the automation of the assembly, the flange is enlarged. The web  25  is then used to detect the position of the constriction/nozzle additionally with respect to the rotation, which web  25  can be detected with an optical sensor during assembly if the device has been installed shifted through 180°. 
         [0061]    The difference between the exemplary embodiments with the bearing cage  60  or without the bearing cage  60  can be summarized as follows. In an exemplary embodiment without a bearing cage  60 , the measuring pipe  11  of the measuring cage  10  or  110  is deformed in such a way that the bearing point is enlarged, with the result that the impeller  50  or  150  can be mounted. As soon as the impeller  50  or  150  is at the assembly position and the bearing cone  56  lies on both sides in the bearing points  166 , this deformation is reversed again, which can be realized through simple removal of the force and elastic deformation. 
         [0062]    On the other hand, when the bearing cage is used, the impeller  50  is firstly mounted in this bearing cage  60  and subsequently fitted into the pipe  11  from the discharge side  13 . The axial assembly takes place here by means of the four catches  17 . It is also in principle possible to provide only two catches  17 . A sprung part, which is realized with the half-round grooves  68 , is provided on the bearing cage  60  itself for fitting in via the four catches  17 . The rotational position itself, that is to say the positioning of the impeller with the correct orientation, is defined by means of the lateral webs which correspond to grooves in the bearing cage  60 . 
         [0063]    The measuring pipe  11  has the said constriction  14  as a nozzle on the supply pipe side  12 , with which nozzle the measuring range is defined. Various nozzle diameters bring about changes in the flow speed of the throughflow liquids. In addition, the device can be adapted to a change in the flow speed to be measured. 
         [0064]    The rotating magnetic field in the case of the rotating impeller  50  is detected by a Hall effect sensor which is fitted into the opening  36  in the housing  30 . Here, in addition to the presented plug solution, with the opposing plug in direct contact on the connection of the Hall effect sensor, it is also possible to provide a cable or direct mounting of the printed circuit board. The separation between the housing  30  and the pipe  10  serves additionally as a double insulation layer. 
         [0065]    In order to keep the contact point of the bearing of the impeller  50  at the smallest possible diameter, preferably two different cone angles are used. In the case of the bearing journal, the angle of the cone  56  with respect to the rotational axis is, for example 40°, whereas the bearing shell, formed by the bearing opening  66 , has a simple angle with respect to the rotational axis of 45°. 
         [0066]    When a magnet  160  enclosed by injection molding is used in the case of the impeller  150 , only one pair of magnet poles is used. This makes it possible to limit the pulse number, which in the case of the size of a model specimen with the dimensions mentioned in the exemplary embodiment gives rise to a throughflow rate of approximately one liter per minute and 22′200 pulses as the order of magnitude. 
         [0067]    The pipes  10 ,  110 , housing  30  and bearing cage  60  are advantageously injection molded parts, if appropriate made of a permanently magnetic material in the case of the impeller. 
         [0068]    The diameter of the impeller  50  is somewhat smaller than the inner diameter of the discharge pipe  13  into which it is inserted. In this context, the feature diameter of the impeller  50  means that the impeller  50  has, when viewed radially over outer faces  52  which respectively lie opposite one another, a diameter measured in this way, or this diameter is determined by the distance between the faces  152 . In this context, the circumcircle diameter of the impeller  50  is smaller than the inner diameter, or each inner diameter, of the discharge pipe  13 . This circumcircle diameter defines the outer diameter corresponding to the impeller  50 , even between the faces  52 - 52  and  152 - 152  lying opposite one another through the hub. Said circumcircle diameter is smaller than the nominal inner diameter of the discharge pipe  13 , which means two things. On the one hand, the nominal diameter is the diameter of the discharge pipe  13  (or see below: of the supply pipe  12 ) which this pipe has over a substantial part. In this context, the inserts such as the bearing cage  60  etc. are not considered. As a result of this relatively large nominal diameter, the impeller  50  can be fitted into the measuring housing via this path, which provides advantages in respect of the tightness and the termination with respect to the sensor housing  30 . 
         [0069]    Since, in particular, the supply pipe  12  advantageously has a diameter which is similar to or the same as the discharge pipe  13 , the diameter of the impeller  50  is also smaller than the inner diameter of the supply pipe  12 . It is therefore possible to specify a single-piece supply pipe/discharge pipe  12 / 13 , as illustrated in section in  FIG. 6 , which has essentially a cylindrical outer shape, as illustrated in  FIG. 10 , which is interrupted merely by connecting fins and connecting flanges, and an identical outer diameter is provided onto which the connecting hoses (not illustrated) can be fitted. There is, in particular, no measuring housing  110  protruding beyond the diameter, as defined above, of the impeller  50 . This results in a reduced space requirement for the measuring housing  110  in contrast to the designs in the prior art. This measuring housing  110  can then be fitted laterally into a recess  35  in the sensor housing  30  and locked and, in particular, clipped in, which permits very simple and space-saving routing of the hose which then surrounds the sensor and leads in and out, with the measuring housing  110  located between them. 
         [0070]      FIG. 11  shows a cross section through an exemplary embodiment of a measuring housing  10  with an impeller  50 , wherein a throughflow restrictor  300  is inserted into the discharge pipe  13  itself.  FIG. 12  shows a perspective view of the throughflow restrictor  13  from  FIG. 11 , and  FIG. 13  shows a plan view thereof. 
         [0071]    The throughflow restrictor  300  has, on its side facing the impeller  50 , a reducing cone  302  which reduces the diameter of the inner pipe of the discharge pipe  13  to the size of the throughflow opening  304 . The size of the throughflow opening  304  is of the order of magnitude of the opening remaining on the supply pipe side  12  downstream of the reducing cone  29  there. The measuring range of the measuring device is defined with the constriction  14  there as a nozzle. On this side, the measuring accuracy is increased by avoiding rebound effects as a result of the pump action. 
         [0072]    Reference is briefly made to  FIG. 14 , which shows four of the total of eight positioning knobs  301  in cross section, on which positioning knobs  301  the throughflow restrictor is attached. In this context, the throughflow restrictor  300  is secured axially in the pipe by means of radial pressure and by means of the knobs  301 . 
         [0073]    The throughflow restrictor  300  has a perimeter wall  312  which is tailored in a closely fitting fashion to the inner diameter of the discharge pipe  13 . Said perimeter wall  312  has two grooves  310  lying opposite one another for receiving the locking elements. For the sake of simpler insertion into the discharge pipe  13 , the perimeter wall  312  is beveled at least at the insertion side  313 . On the side pointing towards the discharge, a depression  320  which extends laterally with respect to the groove  310  is provided, said depression  320  being in the illustrated exemplary embodiment here an injection point of the injection molded part. A fin  330 , which facilitates handling of the throughflow restrictor  300  by engagement by means of a pincer-shaped object for insertion into the discharge pipe  13  is provided radially with respect to the throughflow opening  304 . 
         [0074]      FIG. 14  shows another exemplary embodiment for assembling a throughflow restrictor  400  on the outside of the discharge pipe  13 .  FIG. 15  shows the throughflow restrictor  400  in the perspective view, and  FIG. 16  in a plan view from the discharge side. 
         [0075]    The throughflow restrictor  400  also has a continuous passage opening  404  similar to the abovementioned throughflow opening  303 . Said passage opening  404  is arranged, in particular centrally, in a wall which connects two sleeves  401  and  402  which adjoin one another and are connected in one piece, to the two side faces  405  and  415  which adjoin the diameter. The wall  405 / 415  is continuous on the discharge side in the advantageously relatively narrow discharge-side sleeve  402  which can have, in particular, the diameter similar to the discharge pipe  13 . Here, the wall which has the throughflow opening  404  is, on both sides, a flat side face, which follows the radius, in contrast to the cone  302  on the inside of the throughflow restrictor  300 . It is possible, even in the case of the throughflow restrictor  300 , to have a smooth, supply-side wall, and a cone in this exemplary embodiment. 
         [0076]    On the discharge side, a tubular sleeve  401  is provided which is larger in the inner diameter and which sits, in particular with a force fit on the outer wall of the discharge pipe  13 . In this context, the discharge pipe  13  abuts against the inner wall  405 , said inner wall  405  forming a shoulder. Provided between the two sleeves  401  and  402  is a shoulder  403  which, however, could also be implemented by a junction. The discharge pipe is seated on the inner wall  411  of the sleeve  401  under stress. 
         [0077]    The throughflow restrictor  300  or  400  is arranged on the discharge side, and the impeller  50  is therefore bounded on both sides by a constriction  14  or  304 / 404 . At the location on the supply side where the nozzle  14  defines the measuring range, the constriction  304 / 404  improves the measurement, since usually when these flowmeters are used the device which pumps the liquid is, as it were, arranged downstream as suction points. This pump operates generally with a certain clocking method which generates a different partial vacuum on the discharge side of the measuring device. This change in partial vacuum can bring about falsification of the measurement result. This influence is reduced by inserting the throughflow restrictor  300 / 400  on the discharge side, in particular because the constriction  14  which determines the throughflow corresponds, as a nozzle which is oriented toward the impeller  50 , to the discharge diameter through the constriction  304 / 404 . 
         [0078]    The element  300  or  400  has been referred to as a throughflow restrictor. It generates a pressure loss at the outlet and therefore a reduced throughflow through its constriction  304  or  404 . The diameter of the opening of the throughflow restrictor is larger than or at least of the order of magnitude of its length in the direction of the pipe. The pump which is located downstream thereof can, however, compensate this pressure loss; the flowmeter is, of course, installed on the suction side of the pump. 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 LIST OF REFERENCE NUMBERS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 Measuring housing 
               
               
                 11 
                 Outer pipe 
               
               
                 12 
                 Supply pipe 
               
               
                 13 
                 Discharge pipe 
               
               
                 14 
                 Constriction 
               
               
                 15 
                 Rear wall of constriction 
               
               
                 16 
                 Positioning fin 
               
               
                 17 
                 Ratchet pawl 
               
               
                 18 
                 Flange 
               
               
                 19 
                 Opposing flange 
               
               
                 21 
                 Orientation groove 
               
               
                 22 
                 Upper side 
               
               
                 23 
                 Front side/rear side 
               
               
                 29 
                 Reducing cone 
               
               
                 30 
                 Sensor housing 
               
               
                 31 
                 Side wall 
               
               
                 32 
                 Side wall 
               
               
                 33 
                 Locking tongue 
               
               
                 34 
                 Receptacle rear wall 
               
               
                 35 
                 Receptacle 
               
               
                 36 
                 Sensor receptacle 
               
               
                 37 
                 Plug receptacle 
               
               
                 38 
                 Connecting receptacle 
               
               
                 39 
                 Locking tongue 
               
               
                 41 
                 Deformation clearance region 
               
               
                 42 
                 Line guide 
               
               
                 43 
                 Guide fin 
               
               
                 50 
                 Impeller 
               
               
                 51 
                 Blade 
               
               
                 52 
                 Outer face 
               
               
                 53 
                 Beveled face 
               
               
                 54 
                 Impact face 
               
               
                 55 
                 Side wall 
               
               
                 56 
                 Bearing cone 
               
               
                 57 
                 Widened cone base 
               
               
                 58 
                 Round cone tip 
               
               
                 60 
                 Bearing cage 
               
               
                 61 
                 Ring 
               
               
                 62 
                 Bearing arm 
               
               
                 63 
                 Bearing arm groove 
               
               
                 64 
                 Run-up projection 
               
               
                 65 
                 Guiding groove 
               
               
                 66 
                 Bearing opening 
               
               
                 67 
                 Oval breakthrough 
               
               
                 68 
                 Sprung part 
               
               
                 69 
                 Outer wall 
               
               
                 90 
                 Hall sensor 
               
               
                 110 
                 Measuring housing 
               
               
                 111 
                 Guide fin 
               
               
                 112 
                 Guide groove 
               
               
                 113 
                 Ramp 
               
               
                 150 
                 Impeller 
               
               
                 151 
                 Blade 
               
               
                 152 
                 Outer face 
               
               
                 153 
                 Casting depression 
               
               
                 160 
                 Magnet 
               
               
                 161 
                 Lateral injection-molding enclosure 
               
               
                 166 
                 Bearing opening 
               
               
                 210 
                 Measuring housing 
               
               
                 211 
                 Guiding elevated portion 
               
               
                 213 
                 Ramp 
               
               
                 300 
                 Throughflow restrictor 
               
               
                 301 
                 Knob 
               
               
                 302 
                 Reducing cone 
               
               
                 304 
                 Through-opening 
               
               
                 310 
                 Securing groove 
               
               
                 312 
                 Perimeter wall 
               
               
                 313 
                 Beveled portion 
               
               
                 320 
                 Depression 
               
               
                 330 
                 Fin 
               
               
                 400 
                 Throughflow restrictor 
               
               
                 401 
                 Pipe-side sleeve 
               
               
                 402 
                 Discharge-side sleeve 
               
               
                 403 
                 Shoulder 
               
               
                 404 
                 Through-opening 
               
               
                 405 
                 Inner shoulder 
               
               
                 411 
                 Inner wall 
               
               
                 415 
                 Inner shoulder