Swirler for a fluid flowmeter and method of making same
BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates broadly to fluid flowmeters and is particularly concerned with a novel swirler for a flowmeter and a method of making the same. 
     U.S. Pat. No. 3,616,693 discloses a swirl-type flowmeter containing a swirler of the general type to which the present invention relates. In order to impart the desired swirl to the fluid passing through the flowmeter, immediately adjacent blades of the swirler must be both axially and circumferentially overlapping. While the disclosure of this prior patent fails to address itself to the manner of fabricating the swirler, the drawings thereof suggest that the blades are individually fabricated and then joined to an outer ring which is in turn inserted onto a central hub with each of the blades lodging in a corresponding axial groove in the hub. 
     The present invention is directed to an improvement in the foregoing type of swirler and relates both to the article per se and to the method of its manufacture. An outstanding attribute of the present invention is that the cost of making such a swirler is dramatically reduced. This is because the swirler can be made from two molded plastic parts which are subsequently assembled together. Furthermore, each of the two molded plastic parts can be made by means of simple molding dies. Thus, the invention makes the mass production fabrication of a fluid flowmeter embodying a swirler of this type economically feasible. 
     The accompanying drawings disclose a preferred embodiment of the present invention according to the best mode presently contemplated in carrying out the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view, partly in section, of a fluid flowmeter having a swirler embodying principles of the present invention. 
     FIG. 2 is an axial end view of one of the two elements of the swirler shown in FIG. 1. 
     FIG. 3 is a longitudinal view of the element shown in FIG. 2. 
     FIG. 4 is an axial end view of the second element of the swirler shown in FIG. 1. 
     FIG. 5 is a longitudinal view of the element shown in FIG. 4. 
     FIG. 6 is an exploded view of the two elements illustrating how they are assembled together. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an illustrative, but preferred, embodiment of a fluid flowmeter 10 embodying the present invention which is adapted for use to measure induction airflow into an internal combustion engine as used in a motor vehicle. Flowmeter 10 is provided in the air intake snorkel, or air horn, 12 which projects from the air filter housing 14 and through which air is inducted by the engine, the general direction of airflow being indicated by the arrow A. The swirler 16 embodying principles of the invention is disposed in snorkel 12 at the inlet thereof to impart a swirling motion to the induction air. A sensing probe assembly 18 is located downstream of swirler 16 to detect a characteristic of the swirling air and provide via appropriate circuitry an electrical signal representative of the volumetric flow rate of air through the snorkel. An especially well-suited probe is disclosed in U.S. Pat. No. 3,830,104, assigned to the same assignee as the present application. The improvement provided by the present invention relates specifically to swirler 16. In accordance with principles of the invention, swirler 16 is constructed from two separate elements which are identified by the reference numerals 20 and 22 respectively. Element 20 is shown in detail in FIGS. 2 and 3 while element 22 is shown in detail in FIGS. 4 and 5. Both elements are molded plastic parts which may be fabricated using conventional molding techniques. By way of example glass-filled nylon or polyester are suitable plastics. Element 20 comprises four individual, identical swirling blades 24a, 24b, 24c, 24d, which are uniformly circumferentially arranged about a central hub 26. The radially outer edges of the individual blades are joined at their upstream ends by an integral circular ring 28. As can be seen in FIG. 3 the individual blades project axially downstream of both hub 26 and ring 28. However, as can be seen in FIG. 2, the blades are circumferentially non-overlapping. A circular, conically-rimmed, locating hole 30 is provided in the downstream end of hub 26. Four uniformly, circumferentially arranged locating slots 31 are provided in ring 28 for use in locating the two elements, as will be seen later. 
     Element 22, shown in FIGS. 4 and 5, comprises a plurality of four blades 32a, 32b, 32c and 32d which are uniformly circumferentially arranged around a tapered, hollow central hub 34. Blades 32a, 32b, 32c and 32d are identical to those of element 20 and project slightly axially upstream beyond the upstream end of hub 34 which is provided with a central conical nose 36 adapted to seat on the conically rimmed hole 30 of element 20. As can be seen in FIG. 4 the four blades of element 22 are circumferentially non-overlapping. Four radially directed locating tabs 40 are provided on the blades of element 22 for cooperation with slots 31 in locating the two elements. 
     FIG. 6 illustrates how the elements 20 and 22 are assembled together. The two elements are positioned in substantial axial alignment with each other, with element 22 being disposed in downstream relation to element 20. The two elements are dimensioned with that sufficient circumferential clearance is provided between immediately adjacent blades of element 20 to permit the upstream ends of the blades of element 22 to fit between immediately adjacent blades of element 20 as the two elements are relatively advanced toward each other, for example, as indicated by the arrow 42. As the blades of the two elements are more fully interdigitated, a point is reached where the two elements may then be also relatively rotated as indicated by the arrow 44 to register tabs 40 with slots 31. Final assembly is achieved by lodging tabs 40 into slots 31 (arrow 46) thereby axially and circumferentially locating the two elements with respect to each other. Permanent joining may be accomplished by any suitable means, for example, by means of adhesive, mechanical fasteners, ultrasonic welding etc. As will be apparent from considertion of the drawings, the assembled swirler has the forward, or upstream ends of blades 32a, 32 b, 32c and 32d disposed between hub 26 and ring 28 so that they axially overlap both hub 26 and ring 28 and extend radially therebetween. Also, the portions of blades 24a, 24b, 24c, and 24d which extend axially beyond the hub 26 of their own piece axially overlap and are disposed radially outwardly of hub 34. 
     One principal advantage of the present invention is that the two plastic elements can be molded with maximum dimensional accuracy and maximum production speed. As best seen in FIGS. 2 and 4, neither element 20 nor 22 will create a die interlock condition during molding and hence each can be fabricated using simple, straight parting dies. The two elements can also be assembled together with facility and accuracy. Thus, there has been disclosed a novel swirler and method of making it representing a significant contribution in minimizing the cost of such a device.