Abstract:
A turbine type flow meter has a four-vaned plastic torpedo-shaped turbine mounted by portions of the plastic turbine within a housing between first and second bearings. The turbine supports a pair of magnets of the Neodymium-Iron-Boron type which rotate with the turbine. An upstream portion of the housing incorporates a sensor cavity, which is sealed from a flow cavity containing the turbine. A connector and an attached printed circuit board with a Hall effect sensor is mounted within the sensor cavity closely spaced from the rotating magnets. The sensor housing is constructed from two parts. Each part of the housing incorporates mating structures that are designed for joining by spin welding.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to water flow monitors in general and in particular to flow monitors employing a turbine. 
     Measuring the flow of a fluid in a pipe can be difficult, depending on the level of accuracy required. A positive displacement pump is probably the most accurate conventional approach; however, such pumps are costly, cause a significant pressure drop and are relatively bulky. Simple paddlewheel type sensors may be of low-cost and have little resistance to the flow of fluid, but may suffer from a lack of accuracy over a wide range of fluid flow rates, particularly at low or very high flow rates. 
     Precision flow instruments employ a turbine that passes substantially all the flow. However, bearing friction can seriously impede accuracy at higher flow velocities. The typical solution is to over-design the bearings which support the flow turbine, with the result being a relatively expensive instrument not suitable for use in many commercial and consumer applications, such as boilers, shower pumps, and tank filling applications. Flow monitoring with relative precision is necessary for residential and commercial water meters. Flow monitoring can also detect problems within waterflow systems, and can allow modulation of water flow velocities with greater precision. Flow monitoring can be important in hot water heating systems where monitoring flow assures balanced heating. Flow monitoring can also be used to increase energy efficiency by, for example coordinating water flow with burner activation in a boiler. Monitoring of fluid flow through a pump can assure that adequate fluid flows are present for pump cooling and avoiding cavitation at the pump impeller. 
     What is needed is a turbine type flow monitor that is low-cost, relatively accurate, creates a relatively low-pressure drop, and is resistant to leaks. 
     SUMMARY OF THE INVENTION 
     The turbine type flow meter of the present invention has an in-line housing in which a four-vaned torpedo-shaped turbine is between a first bearing spaced along the axis of flow from a second bearing. The bearings are supported by a plurality of axially extending spokes. The turbine supports a pair of magnets that rotate with the turbine. An upstream portion of the housing incorporates a sensor cavity that is sealed from a flow cavity formed by the flow meter. The sensor cavity is closely spaced from the rotating magnets positioned on the turbine. Positioned within the sensor cavity is a printed circuit board on which a Hall effect sensor is mounted. A connector mounted to the circuit board extends from the sensor cavity. The circuit board is mounted within the sensor cavity so that the Hall effect sensor is positioned close to the rotating magnets of the turbine. A temperature sensor may also be mounted on the circuit board and the circuit board may be potted within the sensor cavity with polyurethane or epoxy. 
     The sensor housing is constructed from two parts: a first upstream part containing the sensor cavity, and a second downstream part containing the downstream bearing. Both the upstream part of the housing and the downstream part of the housing incorporate pipe fittings to allow the turbine housing to be readily positioned along a fluid flow pipe. The upstream housing and the downstream housing incorporate mating structures that are designed for joining by spin welding. 
     It is a feature of the present invention to provide a fluid flow sensor of low cost. 
     It is a further feature of the present invention to provide a fluid flow sensor, which monitors fluid temperature in addition to fluid flow rate. 
     It is a still further feature of the present invention to provide a fluid flow sensor, which is accurate at low fluid velocities. 
     It is a yet further feature of the present invention to provide a fluid flow sensor, which occupies little additional volume beyond the volume, occupied by the fluid piping. 
     Further features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation cross-sectional view of the device of this invention partially broken away to show spin forming a joint. 
     FIG. 2 is a front elevation cross-sectional view of the device of FIG. 1 taken along section line  2 — 2 . 
     FIG. 3 is a front elevation cross-sectional view of the device of FIG. 1 taken along section line  3 — 3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1-3 wherein like numbers refer to similar parts, a flow sensor  20  is shown in FIG.  1 . The flow sensor  20  has a housing  22  that comprises an upstream portion  24 , which incorporates a sensor cavity  26 , and a downstream portion  28 , which are joined by spin welding. The upstream housing portion  24  has an upstream bearing cup  30  supported in the center of a flow passageway  32  by a series of radial spokes  34  that position the bearing cup  30  in the center of the flow passageway  32 . Fluid flows along the passageway  32  as indicated by arrows  33  while the radial spokes  34  allow substantially unobstructed fluid flow along the passageway  32 . Similarly, the downstream housing portion  28  has a downstream bearing cup  36  that is also supported by radial spokes  38  which support the downstream bearing cup  36  in the center of the flow passageway  32 . The downstream bearing cup  36  is surrounded by a centering cone  39 . 
     A turbine body  40  rotates about an axis  41  defined between an upstream trunnion  42  and a downstream trunnion  44 , which are received within the upstream bearing cup  30 , and the downstream bearing cup  36  respectively. The upstream trunnion  42  and downstream trunnion  44  are integrally formed with the turbine body, thus avoiding the need for a metal bearing shaft. Between the upstream trunnion  42  and the downstream trunnion  44  extends a plastic turbine shaft  46 . The shaft  46  has an upstream tapered section  48  which extends from the upstream trunnion  42 , a central cylindrical section  50 , and a rearward conical portion  52 , which terminates in the downstream trunnion  44 . Two magnets  54  are press fit within internally cylindrical cups  56  that extend radially outwardly from the upstream tapered section  48 . The magnets  54  are cylindrical, with the axis of the magnet cylinder positioned to periodically point at the Hall effect sensor. The magnets are preferably of the Neodymium-Iron-Boron type that has a high field strength. The high field strength and the position and shape of the magnets allows the use of a Hall effect sensor which can detect rapid rotation of the magnets  54  on the turbine body  40 . The magnets  54  may be sealed with polyurethane or epoxy to protect them from a fluid flowing through the sensor  20 . The magnets  54  may also be sealed within the material forming the turbine body  40  by the process of overmolding or insert molding. 
     Four equally spaced blades  58  are positioned about the central cylindrical section  50  of the turbine body  40 . Each blade  58  is divided into two portions approximately equally long in the axial direction. The upstream portion  60  is angled with respect to the axis  41  twenty degrees (0.35 radians), and the downstream portion  62  is angled with respect to the axis  41  six degrees (0.105 radians). Both portions of the blades  58  are more nearly parallel to the axis  41  of the turbine body  40 , than is the case with fan type turbine flow sensors. The blades  58  extending along the turbine body are more parallel than not to the axis  41 , in contrast to paddlewheel type turbine blades. 
     As shown in FIG. 2, a circuit board  64  is positioned within the sensor cavity  26 . A Hall effect sensor  66  is mounted on the circuit board, and a resistor  68  is connected across the output of the Hall effect sensor to increase the voltage output. The circuit board  64  is positioned so the magnets  54  pass closely by the Hall effect Sensor  66 . In addition, a temperature sensor  70  may also be located on the circuit board  64 . A connector  72  is joined to the circuit board and extends from the sensor cavity  26  as shown in FIG.  2 . The connector  72  adapts the sensor  20  to function with customer-supplied monitoring circuits. 
     The sensor cavity  26  is separated from the flow passageway  32  by a relatively thin but impermeable wall  74 . The cavity  26  may be filled with potting compound such as epoxy or polyurethane. The sensor housing  22  including the impermeable wall  74  is constructed of Modified PPO (Noryl®) or PPS (Polyphenylene sulphide) PPO (Modified Polyphenylene Oxide). These materials and the potting compound are relatively conductive of heat, and thus the temperature sensor  70  will be relatively accurate and will relatively rapidly perceive a temperature change in the fluid flowing through the flow sensor  20 . Monitoring water temperature can be useful in boiler feed situations as well as hot water heating systems. In addition, the accuracy of the flow meter can be increased by correcting for temperature induced density variations in water flowing through the sensor  20 . 
     The turbine body  40  with integrally formed trunnions  42 ,  44  will preferably be made of a plastic with a low coefficient of friction to minimize bearing friction. Examples of suitable materials are POM (polyacetal engineering polymers) with 1-5 percent-added Polytetrafluoroethylene (PTFE) to reduce friction and wear between components. 
     The turbine body  40  is designed for minimal fluid resistance while at the same time good performance at low velocities. This is accomplished by streamlining the cylindrical cups  56 , which hold the magnets  54 , so that the cups  56  are given a teardrop shape by upstream portions  76 . The upstream portion  60  of the turbine blades  58  extend to nearly completely encompass the radial diameter of a central volume  78  between the upstream bearing cup  30  and the downstream bearing cup  36 . More importantly, the blades extend beyond the flow passageway  32  defined between an inlet  80  at the upstream radial spokes  34 , and an outlet  81  defined by the downstream radial spokes  38 . The upstream portion  60  of the turbine blades also has a relatively large angle of attack of twenty degrees to assure rotation of the turbine body  40  at low flow rates. At the same time, a relatively small angle of attack of six degrees of the downstream portion  62  of the blades  58  help the blades function at high velocity while still allowing a considerable clear area along the turbine within the flow passageway  32  as shown in FIG.  2 . 
     The precision with which the flow sensor  20  operates can be increased by combining temperature compensation together with calibration that accounts for increased frictional losses at higher flow rates. 
     The simplicity of the flow sensor  20  is increased by joining the upstream housing portion  24  to the downstream housing portion  28  by spin welding. Spin welding allows the rapid and high-quality joining of two parts where the mating portions are circular, as seen in the lower portion of FIG. 1 in which the upstream housing  24  has been broken away and a mating structure separated from the receiving structure on the downstream portion  28 . As is understood by those skilled in the art, a spin weld joint such as shown in FIG. 1 may have a number of configurations conforming to the rules which have been developed to provide reliable spin wild joints. 
     The structure as shown in FIG. 1 has a conical ring  82  which has a cone angle which is slightly smaller than the cone angle of a conical groove  84 , and a cone height which is slightly higher than the depth of the grooves  84 . Two U-shaped grooves  86  are formed on the radially outwardly extending sides of the conical ring  82  and conical groove  84 . The two U-shaped grooves  86  define a flash  87  retaining structure, which prevents the flash  87  formed during the spin welding process from extending beyond the housing  22 . The spin formed joint  88  should not result in any inwardly extending flash, and a gap  90  exists between the blades  58  and the housing inner wall  92 . 
     The welding process is accomplished by holding the upstream portion  24  of the housing  22  so that the conical ring  82  points upwardly, and positioning the turbine body  40  with the upstream trunnion  42  in the upstream bearing cup  30 . The turbine body  40  may be held with a mechanical or a magnetic fixture that holds the turbine body  40  in the vertical position. The downstream portion  28  of the housing is rapidly rotated and driven down against the upstream portion  24  the housing, the centering cone  39  which surrounds the downstream bearing cup  36 , may facilitate the downstream trunnion  44  entering into the bearing cup  36 . 
     The flow sensor  20  is easily integrated directly with a pipe and utilizes only a little more space than the pipe alone. The upstream housing portion  24  has a pipe section  94  that can be bonded, retained in a compression fitting or push fit back on to join the flow sensor  20  to a pipe. Similarly, the downstream portion  28  has a pipe section  96  which may be bonded, retained in a compression fitting, or push fit to a downstream pipe. 
     It should be understood that the flow sensor  20  may be designed for use with pipes of various sizes. In particular, the flow sensor illustrated in FIG. 1 is designed to mate with a pipe having an exterior diameter of 15 mm, which is received within the pipe section  94 , and the pipe section  96 . A flow sensor having a scale to join with a 15-mm exterior diameter pipe employs magnets having a diameter of 3 mm and a height of 5 mm. 
     A standard is defined by BS EN 60529 for the notation of the level of protection provided by enclosures of electrical equipment against the environment. The sensor housing  22 , with the encapsulated sensor and the overall construction of the flow sensor  20  allows a sensor in accordance with this disclosure to be built to the IP67 standard. To further test the sensor  20  to assure no leaks are present, a test pressure of approximately 15 atmospheres may be applied to test the integrity of the spin weld. 
     It should be understood that the Hall effect sensor  66  may be a standard digital pulsing type, analog sensor, or a latching sensor depending on the end user. It should also be understood that other magnetic field sensors such as a Giant Magnetoresistive (GMR) device. In addition, for low turbine speeds a reed switch could be used. The high-strength magnets, particularly the Neodymium-Iron-Boron type, make practical using a Hall effect sensor to monitor high turbine rotation speeds. 
     Typically all materials which come into contact with water, within the sensor  20  will meet the various regulatory requirements (e.g. in England, the Water Regulatory Council) for materials coming into contact with potable water. 
     It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces all such modified forms thereof as come within the scope of the following claims.