Abstract:
A flowmeter, in particular for a beverage preparation machine, includes a housing, such as a moulded housing, delimiting a measuring chamber, and a measuring body, such as a moulded body, rotatably mounted in the measuring chamber. The housing and the measuring body are made of at least one of polyoxymethylene, polyformaldehyde or polybutyleneterehpthalate.

Description:
This application is a 371 filing of International Patent Application PCT/EP2010/058690 filed Jun. 21, 2010. 
     FIELD OF THE INVENTION 
     The field of the invention pertains to flowmeters, in particular constitutive materials of flowmeters for beverage preparation machines. 
     For the purpose of the present description, a “beverage” is meant to include any liquid food, such as tea, coffee, hot or cold chocolate, milk, soup, baby food, etc. 
     BACKGROUND ART 
     Certain beverage preparation machines use capsules containing ingredients to be extracted or to be dissolved; for other machines, the ingredients are stored and dosed automatically in the machine or else are added at the time of preparation of the drink. 
     Various beverage machines, such as coffee machines, are arranged to circulate liquid, usually water, from a water source that is cold or heated by heating means, to a mixing or infusion chamber where the beverage is actually prepared by exposing the circulating liquid to a bulk or pre-packaged ingredient, for instance within a capsule. From this chamber, the prepared beverage is usually guided to a beverage dispensing area, for instance to a beverage outlet located above a cup or mug support area comprised or associated with the beverage machine. During or after the preparation process, used ingredients and/or their packaging is evacuated to a collection receptacle. 
     Most coffee machines possess filling means that include a pump for liquid, usually water, which pumps the liquid from a source of water that is cold or indeed heated through heating means, such as a heating resistor, a thermoblock or the like. For instance, U.S. Pat. No. 5,943,472 discloses a water circulation system for such a machine between a water reservoir and a hot water or vapour distribution chamber, for an espresso machine. The circulation system includes valves, a metallic heating tube and a pump that are interconnected with each other and with the reservoir via a plurality of silicone hoses that are joined together by clamping collars. 
     To control the characteristics of the liquid circulated to the mixing or infusion chamber, e.g. quantity and/or speed, such machines typically include a flowmeter. The flowmeters used in such beverage machines are made of food safe materials at least where exposed to the circulating fluid and have to be economically affordable to be used in such machines. 
     For instance, EP 0 841 547 discloses a flowmeter commercialised by DIGMESA which is suitable for beverage preparation machines. This flowmeter has a two-part housing with a bayonet connection, the housing containing an inner measuring chamber with a central fixed shaft extending therethrough for mounting an inner rotatable measuring body with fins that are located in the flow path and that are driven thereby. The flow of liquid passing through the measuring chamber is derived from a measure of the speed of rotation of the rotatable measuring body using a Hall sensor. A drawback of this device lies in the large friction surface between the fixed shaft and the rotating measuring body which changes depending on the orientation of the flowmeter and which also affects the accuracy of the measure of the flow through the chamber. 
     U.S. Pat. No. 4,666,061 discloses a similar flowmeter for beverage dispenser lines for wine, mineral water or beer that can be easily disassembled and reassembled for cleaning. The flowmeter has a two-part housing assembled by a bayonet connector and enclosing a measuring chamber. The chamber contains a centred rotatable measuring body having a rotatable shaft held in pace by a pair of facing diamond point bearings mounted into the housing and extending into the chamber. A drawback of this device lies in the price of the diamond point bearings and the required assembly steps for mounting such point bearings into the housing of the flowmeter. 
     Hence, there is still a need to provide an accurate inexpensive flowmeter, in particular for use in a beverage preparation machine. 
     SUMMARY OF THE INVENTION 
     The invention thus relates to a flowmeter, in particular for a beverage preparation machine. The flowmeter comprises: a housing, such as a moulded housing, delimiting a measuring chamber; and a measuring body, such as a moulded body, rotatably mounted in the measuring chamber. The housing and the measuring body are made of at least one of POM and PBT. 
     In particular, the housing and the measuring body are respectively made of POM (e.g. polyoxymethylene or polyformaldehyde), as Schulaform 9A, and PBT (e.g. polybutylenterephthalate), such as Tecdur GK30, or vice versa. Hence, the housing may be made of POM and the measuring body of PBT, or the housing may be made of PBT and the measuring body of POM. 
     In so far as the flowmeter is used in a beverage preparation machine, the materials forming the chamber and the rotatable measuring body with the shaft should be food safe. Furthermore, they should have a low friction coefficient and a low abrasion rate and be well controllable in the manufacturing/moulding process so as to achieve high dimensional precision to provide a high quality flowmeter at limited cost. Moreover, these materials should be so controllable in the manufacturing process, e.g. moulding, as to permit the formation of small-sized reliable parts to be able to reduce the size of the device in which such a flowmeter is integrated for use. All these requirements are fulfilled by using the abovementioned materials, in particular in combination. 
     The abrasion rate of the POM material against the PBT material can be of about 0.2 μm/km. The abrasion rate of the PBT material against the POM material is typically of about 0.7 μm/km. Moreover, such POM and PBT materials are food safe. Such an abrasion rate provides a long lifetime for inexpensive moulded flowmeters, e.g. for use in beverage preparation machines. 
     In an advantageous embodiment, the moulded housing and/or the moulded measuring body include a stabilising filler, such as beads, in particular glass beads. In this case, the composite material, including a filler and a POM or PBT binder, can be used to manufacture the corresponding part of the flowmeter. The stabilising filler may represent 10 to 70 vol % of said housing and/or the measuring body ( 3 ), in particular 15 to 50 vol % such as 20 to 40 vol %. 
     The use of a filler material such as beads leads to an increased control of the shrinkage of the composite material when it consolidates during the moulding step. This is particularly desirable for insuring a high dimensional precision of the relatively movable parts and for a proper assembly of the parts. Moreover, the use of beads instead of fibres, e.g. glass fibres, as a filler material provides clean surfaces which can be manufactured with tight tolerances in particular for the bearings. Furthermore, the use of beads as a filler material reduces the friction coefficient and abrasion rate compared to the use fibre material as a filler. The components produced from such a composite material also exhibit a high stability, in particular for the connecting part, as discussed below. 
     Typically, the housing is made of two assembled moulded bodies, the housing having in particular a cup-like body and a cover body. For instance, the cup-like body has a rim and the cover body has a seal lip, the seal lip being force-fitted into the rim, or vice versa, for sealing the cover body on the cup-like body. 
     In an embodiment, the rotatable measuring body has a rotatable shaft extending across the measuring chamber, the shaft being rotatably mounted and positioned in the measuring chamber at opposite extremities of the shaft by point bearings. For instance, the shaft is a rotor or like element with flow intercepting parts such as fins or blades, typically an impeller. Each point bearing may be formed of a protruding part and a cooperating facing counter-part part, in particular a recessed part, associated, respectively, with the housing and an extremity of the rotatable shaft, or vice versa. The protruding part and the counter-part are advantageously integrally formed with their associated moulded housing and moulded rotatable shaft. 
     In one embodiment, the housing comprises facing protrusions extending into the chamber for forming the point bearings. Alternatively, the protrusions may be located on the shaft of the measuring body. It is also possible to provide a mixed configuration, i.e. a first bearing with the protrusion on the shaft and a second (opposite) bearing with the protrusion on the housing. 
     The rotatable shaft typically has a rotation axis that extends between a point bearing located at a cover body of the housing and a facing point bearing located in a cup-like body of the housing. 
     The cup-like body may have a rim forming a reference surface perpendicular to the shaft&#39;s rotation axis, the cover body having an inner face that is urged against the reference surface for precisely setting a spacing between these point bearings so as to hold and allow free rotation of the shaft therebetween. 
     The bodies forming the housing can be assembled by a snap, latch, clamp or hook arrangement, in particular by a bayonet connection. 
     Thus, the manufacturing costs of such flowmeter that does not require a diamond element for the bearing are significantly reduced. The two bearing parts can be formed during a moulding step of the components they are respectively associated with. The bearing parts can be integrally formed with the static support component and with the moving measuring component, respectively, and no separate assembly step is required therefor which limits the production costs. The accuracy of the flowmeter is however largely independent from the orientation of the flowmeter. The protruding part and/or counter-part of each point bearing can be made by fusion/solidification and/or polymerization of materials, usually by moulding these materials. 
     Each of the moulded bodies forming the housing may have a through-opening communicating with the measuring chamber for circulating liquid through such flowmeter. 
     The housing can include a connecting arrangement for disconnectably connecting a sensor device thereto, in particular a Hall sensor device. 
     The invention also relates to a beverage preparation machine having a liquid circulation circuit, in particular a water circulation circuit, that comprises a flowmeter as described above. 
     For instance, the machine is a coffee, tea or soup machine, in particular a machine for preparing within an extraction unit a beverage by passing hot or cold water or another liquid through a capsule or pod containing an ingredient of the beverage to be prepared, such as ground coffee or tea or chocolate or cacao or milk powder. The machine may comprise a brewing unit for housing this ingredient. Typically, the machine includes one or more of a pump, heater, drip tray, ingredient collector, liquid tank and fluid connection system for providing a fluid connection between the liquid tank and the brewing unit, etc. The configuration of a fluid circuit between the liquid reservoir and a heater for such a machine is for example disclosed in greater details in co-pending application PCT/EP08/067072. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the schematic drawings, wherein: 
         FIG. 1  shows an exploded view of a flowmeter according to the invention, the assembled flowmeter being shown in  FIG. 2 ; 
         FIG. 3  illustrates part of an electric connector for such a flowmeter; and 
         FIG. 4  illustrates part of the housing of such a flowmeter. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  illustrate a flowmeter  1  typically for a beverage preparation machine such as a coffee machine. The flowmeter may be mounted in the fluid circuit of the beverage preparation machine as for example described in greater details in PCT/EP09/053368. 
     Flowmeter  1  has a housing formed of two assembled moulded bodies  2 , 4  delimiting an internal generally cylindrical measuring chamber  10 . For example, the housing is formed by injection moulding. 
     Housing  2 , 4  contains a rotatable measuring body  3  in the form of a rotor or impeller. Body  3  has a series of radial members  31 , e.g. fins or blades, on a rotatable shaft  32  extending centrally across the measuring chamber  10 . Shaft  32  has a lower part  33  from which radial members  31  extend and an upper part  34 . Two cavities  35  are provided in upper part  34  for housing a pair of magnets  36  of corresponding shape. Shaft  32  or body  3  may be manufactured by injection moulding as well 
     Flowmeter  1  has upper and lower point bearings for mounting opposite extremities  32 ′, 32 ″ of rotatable shaft  32  in housing bodies  2 , 4 . These point bearings are formed by protrusions of housing  2 , 4  extending into chamber  10  and by recesses in extremities  32 ′, 32 ″ of rotatable shaft  32  forming a positioning counter-part for the protrusion, a lower protrusion in the form of a pin  11  and an upper recess  37  of this type forming part of the lower and upper bearings can be seen in  FIG. 1 . The lower and upper bearings are identical to ensure similar performance in all possible orientations. 
     Protrusions  11  and counter-parts  37  are integrally formed with the moulded housing bodies  2 , 4  and the rotatable shaft  32 , respectively. In other words no additional component is needed for forming the bearing parts of the flowmeter. These may be moulded directly with the respective components, i.e. housing bodies  2 , 4  and shaft  32 . The shaft or even the entire impeller  3  (except magnets  36 ) can be made of POM; housing  2 , 4  can be made of PBT with 30 vol % glass beads as a filler. 
     As illustrated in  FIG. 1 , lower housing body  4  is in the general shape of a cup and upper housing body  2  is in the general shape of a cover. It is understood that the lower and upper orientation merely refer to the particular orientations of the flowmeter as illustrated in the Figures. During use, flowmeter  1  may take any orientation or even change orientation. 
     Rotatable shaft  32  has a rotation axis  3 ′ that extends between a point bearing (not shown) located at cover body  2  and a facing point bearing  11  located in cup-like body  4 . 
     Cup-like body  4  has a rim  41  forming a reference surface  42  perpendicular to rotation axis, cover body  2  having an inner face  22  that is urged on reference surface  42  for precisely setting a spacing between the point bearings  11  so as to hold and allow free rotation of shaft  32  therebetween. 
     Furthermore rim  41  has an upright inner surface  43  cooperating with a corresponding seal lip  23  of cover body  2  for sealing cover body  2  on cup body  4  by force-fitting of lip  23  into the rim  41 . This assembly is shown in greater details in the cross-section of  FIG. 4 , in which the same numeric references designate the same elements. A hatched part  23 ′ illustrates the deformation of lip  23  due to the force fitting. In a variation, lip  23  and rim  41  may be welded, e.g. by ultrasonic welding, in which case hating  23 ′ would illustrate the welded portions. 
     Cup-like body  4  has four spaced apart hooks  45  that are evenly distributed on rim  41  and that cooperate with corresponding passages  25  and hook retaining parts  26  at the periphery of cover body  2  to form a bayonet connection. As the locking movement of cover body  2  on cup body  4  is in a plane perpendicular to shaft  32  and rotational axis  3 ′, the spacing between the point bearings is not affected by this locking. This spacing is entirely determined by the geometry (and position) of reference surface  42  so that tight tolerances for the bearings can be provided even though they are formed by moulding and not by additional diamonds. 
     Each of the moulded bodies  2 , 4  has a through-opening communicating with measuring chamber  10  for circulating liquid through such flowmeter. A tubular inlet  47  is provided in cup-like body  4  and a tubular outlet  27  is provided in cover body  2 . The inlet and the outlet could of course be switched. Moreover, the inlet and the outlet could be located on the same moulded body. 
     Furthermore, cover body  2  has a socket  28  with a cavity  29  for receiving a sensor plug  5  as shown in  FIG. 2 , the plug itself being illustrated in greater details in  FIG. 3  in which the same numeric references designate the same elements. 
     Sensor plug  5  has a housing  51  which may be closed with a lid or otherwise sealed (not shown). Housing  51  has a pair of front hooks  52  for securing plug  5  in cavity  29  and delimits an inner chamber  53 . 
     Chamber  53  contains a Hall sensor on a PCB  54  with cables  55  for connection to a control unit (not shown), for instance of a beverage preparation machine such as a coffee machine. To achieve a safe insulation of the PCB from any liquid circulating via chamber  10 , a triple barrier is provided: the walls of socket  28  in cover body  2 , housing  51  of plug  5  and a Kapton or other polyimide foil around PCB  54 , whereby PCB  54  with the Hall sensor is safely sealed. 
     The Hall sensor, PCB  54 , housing  51  and cavity  29  are so arranged and positioned that when plug  5  is secured in socket  28 , the Hall sensor is situated above extremity  32 ″ with magnets  36 . 
     PCB  54  may be formed as part of a main board of the control unit to which cables  55  are connected. Hence, PCB  54  may be manufactured together with the control unit and then separated therefrom, e.g. cut away or broken off along a weakened line, before or after assembly of plug  5  before or after connection of cables  55 , and then secured with plug  5  into socket  28 . Hence, the manufacturing of the sensor device and its control unit can be simplified and optimised. In some embodiment, the flowmeter may even be mounted directly onto the main board so that PCB  54  is an integral part of the main board and remains an integral part of the main board of the control unit, for instance as illustrated in greater details in WO 2009/043865 and in PCT/EP09/053368. 
     During use of flowmeter  1 , liquid is circulated from inlet  47  to outlet  27  via chamber  10 . The flow of liquid will be intercepted by blades  31  thus driving shaft  32  in rotation about axis  3 ′ between the point bearings at extremities  32 ′, 32 ″ of shaft  32 . The speed of rotation of shaft  32  will be proportional to the flow of liquid in chamber  10  and driving measuring body  3 . By rotating shaft  32 , magnets  36  are rotated adjacent to the Hall sensor on PCB  54  that will detect the rotating magnetic field generated by the magnets and convert it into a corresponding electric signal having a frequency corresponding to the speed of rotation of shaft  32 . The information regarding the flow of liquid will then be communicated to a control unit via cables  55 .