Hair dryer heater section providing uniform outlet air temperature distribution
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to hairdrying appliances. More particularly, the invention relates to heater sections used in hair dryers for generating heat. 
     2. Description of the Prior Art 
     Hair dryers for drying hair generally comprise a motor for driving a fan to blow air past heated coils of resistance wire. The motor, fan and resistance wire are included in a dryer housing which may be attached to a handle and the hot air is blown out of a nozzle in one end of the housing. 
     The heater sections of prior art dryers generally comprise resistance wire spirally wrapped about an electrically insulated support frame made of, for example, mica boards and axially interposed in the air stream generated by the fan. One such heater section using coils of wire wrapped around a support board is shown in U.S. Pat. No. 4,260,875 assigned to the assignee hereof. In this type of construction the motor is mounted upstream from the support frame. Another type of heater section comprises a single continuous length of sinusoidally shaped resistance wire (as opposed to a coil) spirally wrapped around a similar frame. In these embodiments the frame consists of a conventional crossed pair of mica boards. The radially distal edges of the mica boards are notched in a saw-tooth pattern to receive the wire which is then connected at predetermined points along its length to a current source. The wire may obviously be connected to the current source at each end to generate the maximum heating ability and various portions of the wire may be connected to a current source by means of taps interposed along the length of the wire. 
     Another type of known heater section utilizing spirally wound, sinusoidally shaped wire includes a hollow cylinder axially aligned with the air flow and having a plurality of insulating boards radially extending from the external surface of the cylinder with the wire wound around the exposed edges of the insulating boards. In this embodiment the motor is situated within the cylinder with the motor output shaft and attached fan extending from one end of the cylinder. 
     Both of the aforementioned types of heater sections are inefficient in the distribution of heat at the nozzle output of the hair dryer. Because the resistance wire is essentially concentrically wound about the axis of the hair dryer near the interior of the housing, the air coming out of the nozzle is relatively cool along the axis and extremely hot near the edge of the nozzle. This type of unbalanced temperature distribution occurs in conventional coiled resistance wire heaters as well as those utilizing sinusoidally shaped wire wound about a cylindrical core. 
     The extremely high tenperatures near the edges of the nozzle create an obvious safety hazard. Such an uneven temperature distribution also necessitates careful selection of the material of the nozzle to enable it to sufficiently withstand such extreme temperatures (on the order of 250° C.). Moreover, such an inefficient temperature distribution necessitiates operating the resistance wire at an unacceptably high level of current in order to produce an acceptable overall temperature output from the hair dryer. This necessarily shortens the life of the heater section. 
     While the aforementioned U.S. Pat. No. 4,260,875 discloses the use of apertures in the mica boards in order to enhance air circulation within the dryer housing, this air circulation is helpful to more uniformly distribute temperature at the nozzle output, but nevertheless insufficient to efficiently distribute output temperature. 
     Consequently, it is an object of this invention to provide a heater secton capable of outputting an air flow having a more uniform temperature distribution. Also, it is another object to provide a heater section capable of generating sufficient amounts of heat at lower average operating currents and temperatures of resistance wire. 
     SUMMARY OF THE INVENTION 
     The aforementioned objects are accomplished by a heater section constructed in accordance with the principles of the present invention which comprises a spirally wound sinusoidally shaped resistance wire, wound about an axially aligned frustoconical/cylindrical motor shroud provided with perforated insulating boards radially extending from its external surface. The motor shroud has a cylindrical portion which is provided with internal, radially extending ribs for receiving the fan motor, the ribs producing a space between the internal surface of the shroud and the motor housing for enabling cooling air to blow past the motor as the main air stream is blown past the resistance wire. The downstream end of the cylindrical portion of the motor shroud is provided with a frustoconical extension for enhancing turbulance within the heater section to facilitate heat distribution at the nozzle opening. The perforations in the individual insulating boards enable circulatin of the heated air spirally about the motor shroud thereby also facilitating heat distribution. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cut away side elevational view of a heater section constructed in accordance with the principles of this invention shown adjacent a fan and dryer housing. The resistance wire is only partially shown for clarity. 
     FIG. 2 is a front view of FIG. 1 taken along line 2--2 wherein the dryer housing and all but a portion of the first loop of resistance wire have been omitted for clarity. 
     FIG. 3 is a side elevational view of a portion of FIG. 1 showing the frustoconical/cylindrical motor shroud without the insulating boards; 
     FIG. 4 is a right side elevationed view of FIG. 3 showing the interior of the motor shroud; 
     FIG. 5 is a cross sectional view of FIG. 3 taken along line 5--5. 
     FIG. 6 is an diagrammatic plan view of a single insulating board. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1 there is shown a heater section 10 constructed in accordance with the principles of this invention. Heater section 10 includes sinusoidally shaped resistance wire 11 and is shown in proper relationship within a hair dryer 12 having a handle 13, base portion 14 and nozzle shroud or housing 16. It will be understood that dryer 12 may be either battery operated or provided with a cord (not shown) for connection to a source of electrical power. Handle 13 may be provided with conventional on/off, fan speed and heat level switches (not shown). Base portion 14 comprises of a conventional fan assembly 18 which has a plurality of fan blades 20 and is secured to output shaft 22 of motor 24 (shown in phantom). A fixed vane assembly 26 which has a plurality of vanes 28 secured to base portion 14 is situated downstream of fan 18. Vane assembly 26 has an axially aligned bore 30 for receiving and holding motor 24 therein. 
     Nozzle portion 16 has a cylindrical portion 32 integrally formed with a frustoconical portion 34. The internal surface of portions 32 and 34 generally follow the contour of the resistance wire support frame 36. Nozzle portion 16 has a nozzle opening 38 having a grill 40 integrally formed into nozzle portion 16. As will be understood below, the ability of the invention to generate satisfactory output air temperature at relatively low current levels enables the resistance wire to operate at lower temperatures therefore enabling use of nozzle portion 16 without a protective internal sleeve which is generally required in prior art dryers. 
     Heater section 10 comprises hollow support frame 36 which has a cylindrical portion 50 and a frustoconical portion 52 axially aligned and secured to the downstream end of portion 50. The relationship of frame 36 to the other portions of dryer 12 is best seen in FIG. 1. It will be noted that heater section 10 is aligned adjacent to base portion 14, downstream of fan 18. Motor 24, as stated above, is held within bore 30 and extends axially from base portion 14 into the interior of support frame 36. 
     Support frame 36 is best seen by reference to FIGS. 2 and 3-5. In the preferred embodiment support frame 36 is made in a one-piece molded configuration of a suitable high-temperature plastic material. The exterior surface of frame 36 is provided with a plurality of radially extending axially aligned ribs 54 each of which is provided with a longitudinal radially outwardly facing groove 56. Each groove 56 is for receiving the end of insulating mica board 60, each board being provided with apertures 62 and 64 and having a predetermined number of notches 66 along the radially distal edge of each board. As will be best seen in FIG. 2, the sinusoidally shaped resistance wire is wound about the radially distal edges of all the insulating boards and the notches 66 serve to retain the wire in position. (Note that, for clarity, the spirally wound wire is only partially shown in FIG. 1 and is shown in FIG. 2 only along a portion of the smallest loop.) 
     It will be noted that the radially distal edge of each insulating board 60, best seen in FIG. 6, is shaped so that the wire, when wound about all the boards, generally conforms to a segmented cylindrical surface having a segmented frustoconical surface downstream thereof. The size of each insulating board is chosen such that the surface formed by the resistance wire is within a predetermined distance 67 from the nozzle portion 16. 
     Referring now to FIG. 3 there is shown another side elevational view of support frame 36 showing the individual ribs 54 and a thermostat mounting post 68 axially extending parallel to the ribs 54. As will be appreciated by those skilled in the art from FIGS. 2 and 3 the thermostat mounting post 68 is situated and shaped in such a way (generally a trapezoidal cross-section) as to facilitate mounting thermostate 69 on support frame 36 before or after the wire has been wound on the frame. Aperture 70 enables a wire lead (not shown) to be connected from one end of thermostat 69 (best seen in FIG. 1) to the electrical circuit in a manner well known to those skilled in the art. 
     Referring now to FIGS. 4 and 5 it will be noted that the internal surface of support frame 36 is provided with a plurality of radially inwardly extending ribs 74. All of the ribs 74 cooperate to form a compression fit about the external cylindrical housing of motor 26 shown in phantom in FIG. 4 when support frame 36 is placed into its operating position. It will be noted that a plurality of apertures 76 are formed between the internal surface of support frame 36 and motor 26. As will be noted by reference to FIGS. 1 and 5, unheated air blown by fan 18 passes through apertures 76 and out aperture 77 and has a cooling effect on motor 26. 
     As will be noted from FIG. 6 each of the individual insulating boards 60 includes apertures 62 and 64 as well as a rectanglar cut-out 78 and a substantially hemispherical cut-out 80. Notch 78 is provided to receive a small retaining plate 82 (best seen in FIG. 1) adhesively bonded to the radially distal edge of each rib 54 to hold boards 56 in place. Cut-outs 80 are provided to enhance circulation at the down stream of heater section 10. 
     For clarity, most electrical connections, wire leads and taps necessary to connect wire 11, motor 26 and thermostat 69 to a source of power have been omitted. In the preferred embodiment shown wire 11 is actually comprised of two parallel wire strands 11a and 11b, each connected at one end to terminal connections 88 and 89, respectively, via crimped end tabs 90. This parallel construction facilitates variations of heat output from the dryer. Terminal connections 88 and 89 and the other ends of wires 11a and 11b are connected by means not shown in a conventional manner so as to produce a functional heater. Various taps, also not shown, may be crimped to either wire 11a and 11b at predetermined points to also facilitate production of various heat levels. 
     It will be understood by those skilled in the art that numerous modifications and improvements may be made to the preferred embodiment disclosed herein without departing from the spirit and scope thereof.