Abstract:
A hair care appliance including a body having an outer wall and an inner wall, a fluid flow path extending from a fluid inlet to a fluid outlet wherein the fluid outlet is at least partially defined by the inner wall, a heater for heating fluid in the fluid flow path and, a thermistor for measuring the temperature of fluid between the heater and the fluid outlet, wherein the thermistor is retained with respect to a housing and the housing forms part of the inner wall. The housing may comprise a base that engages with the inner wall. The housing may further comprise an arm wherein the arm supports the thermistor and extends radially inwards of the inner wall. The housing may comprise two arms and the thermistor is suspended between the two arms. The inner wall may comprise an aperture into which the housing is inserted.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of United Kingdom Application No. 1518642.2, filed Oct. 21, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to a handheld appliance and in particular a hair care appliance such as a hairdryer. 
       BACKGROUND OF THE INVENTION 
       [0003]    Generally, a motor and fan are provided which draw fluid into a body; the fluid may be heated prior to exiting the body. The motor is susceptible to damage from foreign objects such as dirt or hair so conventionally a filter is provided at the fluid inlet to the blower. The fan and heater require power in order to function and this is provided via internal wiring from either a mains power cable or batteries attached to the appliance. 
         [0004]    Conventional hairdryers have control buttons which can change one or more of the flow rate and the temperature of the fluid that exits the hairdryer. However, if the flow rate is increased there is usually a drop in the temperature of the fluid that exits the hairdryer that can be perceived by the user. 
         [0005]    The temperature of the fluid that exits the hairdryer is also affected by other factors. There can be an electrical failure of some sort; alternatively dust and dirt can be pulled into the heater element and if this builds up it can burn and cause an increase in the temperature of the fluid exiting the hairdryer. Obviously, thermal protection is provided in the form of thermal cut outs such as thermal fuses or bi-metallic strips to prevent an excessive increase in temperature but such protection renders the hairdryer inoperable either temporarily or permanently. 
         [0006]    It would be desirable to monitor the temperature and account for thermal fluctuations either due to a change in the flow rate or due to another factor. This provides a better user experience as changes in temperature when the flow rate is changed are minimised. Also, an increase in the temperature without a change in the set flow rate could be used to highlight a possible later problem and prevent the hairdryer becoming inoperable even if for only a short period of time. 
       SUMMARY OF THE INVENTION 
       [0007]    According to a first aspect, the invention provides hair care appliance comprising a body having an outer wall and an inner wall, a fluid flow path extending from a fluid inlet to a fluid outlet wherein the fluid outlet is at least partially defined by the inner wall, a heater for heating fluid in the fluid flow path and, a thermistor for measuring the temperature of fluid between the heater and the fluid outlet, wherein the thermistor is retained with respect to a housing and the housing forms part of the inner wall. 
         [0008]    Having the thermistor downstream of the heater is advantageous compared to having it located within the heater as the thermistor measures the exit temperature of the heater rather than an internal temperature. So, for example if a hot spot is produced within the heater due to an accumulation of dirt and dust this would only be measured if it was located upstream of the thermistor thus, the entire heater is not monitored. 
         [0009]    Preferably, the housing comprises a base that engages with the inner wall. 
         [0010]    It is preferred that the housing further comprises an arm wherein the arm supports the thermistor and extends radially inwards of the inner wall. 
         [0011]    Preferably, the housing comprises two arms and the thermistor is suspended between the two arms. By suspending the thermistor, it is surrounded by the fluid flow so it is not insulated or shielded from the fluid flow and will therefore give a more accurate measure of the actual temperature. 
         [0012]    It is preferred that the inner wall comprises an aperture into which the housing is inserted. This feature is useful for a number of reasons: manufacture is simplified; and repeatability of the positioning of the thermistor is assured for example. 
         [0013]    Preferably, the inner wall comprises a flange which extends at least partially around the aperture. 
         [0014]    It is preferred that the base of the housing comprises a lip which extends radially around the base for engagement with the flange when the housing is positioned correctly with respect to the inner wall. This means that the radial positioning of the thermistor within the heated flow is reliably repeated. 
         [0015]    Preferably, the aperture comprises a stop feature for engagement with the housing when the housing is positioned correctly within the inner wall. 
         [0016]    It is preferred that the stop feature is a recess provided in a wall that defines the aperture. 
         [0017]    Preferably, the housing comprises a cooperating stop feature for engagement with the inner wall when the housing is positioned correctly within the inner wall. 
         [0018]    It is preferred that the base of the housing comprises a strut adapted to extend into the aperture and the strut comprises the cooperating stop feature. 
         [0019]    Preferably, the cooperating stop feature comprises a protrusion adapted to fit within the aperture. 
         [0020]    It is preferred that the strut extends between a pair of arms that extend from the base of the housing. 
         [0021]    Preferably, the thermistor is electrically connected to a control circuit via wiring which extends within the housing. 
         [0022]    It is preferred that the wiring extends from the housing to a printed circuit board (PCB) and the wiring is connected to the PCB via a connector. 
         [0023]    Preferably, the heater comprises a heater element and a wall which extends radially around the outer periphery of the heater element. This wall is preferably made from an insulating material such as Mica. 
         [0024]    It is preferred that the wiring extends along an outer periphery of the wall to the PCB. The wall thermally insulates the wiring. 
         [0025]    Preferably, the inner wall comprises a pair of lips which extend around the inner wall at a distal end of the inner wall from the fluid outlet. 
         [0026]    It is preferred that the pair of lips is adapted to engage with the wall. 
         [0027]    Preferably, the inner wall comprises at least one channel for accommodating the wiring, the at least one channel extending from an end of the inner wall distal from the fluid outlet. This both locates the wiring in a repeatable and known position and it allows the wiring to be recessed into the inner wall providing a degree of protection during manufacture and assembly and a small space saving. 
         [0028]    It is preferred that the at least one channel extends from an aperture in the inner wall wherein said aperture retains the housing within the inner wall. 
         [0029]    Preferably, the PCB is housed within the body and between the PCB and the heater a baffle is provided. 
         [0030]    It is preferred that the baffle comprises a channel for guiding the wiring along a surface of the baffle. This both locates the wiring in a repeatable and known position and it allows the wiring to be recessed into the inner wall providing a degree of protection during manufacture and assembly and a small space saving. 
         [0031]    Preferably, the baffle comprises a retaining clip for retaining the wiring within the channel. 
         [0032]    It is preferred that the retaining clip extends at least partially across the channel. 
         [0033]    Preferably, the appliance is a hairdryer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0035]      FIG. 1  shows a hairdryer in which a thermistor according to the invention may be used; 
           [0036]      FIG. 2  shows a cross section through the hairdryer of  FIG. 1 ; 
           [0037]      FIG. 3  shows an isometric view of a thermistor according to the invention; 
           [0038]      FIG. 4  shows a front isometric view of the thermistor of  FIG. 3  in situ with respect to a heater assembly; 
           [0039]      FIG. 5  shows a front isometric view of the thermistor of  FIG. 3  in situ with respect to the internal structure of the hairdryer body; 
           [0040]      FIG. 6 a    shows a partial cross section through the inner wall of the body of the hairdryer of  FIG. 1 ; and 
           [0041]      FIG. 6 b    shows a partial cross section through the inner wall showing the thermistor in position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0042]      FIGS. 1 and 2  show an example of hairdryer  10  with a handle  20  and a body  30  suitable for use with a thermistor according to the invention. The handle has a first end  22  which is connected to the body  30  and a second end  24  distal from the body  30  and which includes a primary fluid inlet  40 . Power is supplied to the hairdryer  10  via a cable  50 . At a distal end of the cable  50  from the hairdryer  10  a plug (not shown) is provided, the plug may provide electrical connection to mains power or to a battery pack for example. 
         [0043]    The handle  20  has an outer wall  200  which extends from the body  30  towards a distal end  24  of the handle. At the distal end  24  of the handle an end wall  210  extends across the outer wall  200 . The cable  50  enters the hairdryer through this end wall  210 . The primary fluid inlet  40  in the handle  20  includes first apertures that extend around and along  42  the outer wall  200  of the handle in a series of rows and/or columns that extend from the distal end  24  of the handle  20  and second apertures that extend across  46  and through the end wall  210  of the handle  20 . The first and second apertures form an initial filter for the primary fluid inlet and help to prevent hair and other foreign objects from entering. Ideally, a second finer filter  44  is provided. The cable  50  is located approximately in the middle of the end wall  210  so extends from the centre of the handle  20 . The handle  20  has a longitudinal axis X-X along which the outer wall  200  extends from the body  30  towards the distal end  24 . 
         [0044]    Upstream of the primary fluid inlet  40 , a fan unit  70  is provided. The fan unit  70  includes a fan and a motor. The fan unit  70  draws fluid through the primary fluid inlet  40  towards the body  30  through a primary fluid flow path  400  that extends from the primary fluid inlet  40  and into the body  30  where the handle  20  and the body  30  are joined  90 . The body  30  has a first end  32  and a second end  34 , the primary fluid flow path  400  continues through the body  30  towards the second end  34  of the body, around a heater  80  and to a primary fluid outlet  440  where fluid that is drawn in by the fan unit exits the primary fluid flow path  400 . The primary fluid flow path  400  is non-linear and flows through the handle  20  in a first direction and through the body  30  in a second direction which is orthogonal to the first direction. 
         [0045]    The body  30  includes an outer wall  360  and an inner duct  310 . The primary fluid flow path  400  extends along the body from the junction  90  of the handle  20  and the body  30  between the outer wall  360  and the inner duct  310  towards the primary fluid outlet  440  at the second end  34  of the body  30 . 
         [0046]    An inner wall  260  extends within the outer wall  360 . The inner wall  260  at least partially defines the primary fluid outlet  440  and extends from the second end  34  of the body  30  between the inner duct  310  and the outer wall  360 . 
         [0047]    Another fluid flow path is provided within the body; this flow is not directly processed by the fan unit or the heater but is drawn into the hairdryer by the action of the fan unit producing the primary flow through the hairdryer. This fluid flow is entrained into the hairdryer by the fluid flowing through the primary fluid flow path  400 . 
         [0048]    The first end  32  of the body includes a fluid inlet  320  and the second end  34  of the body includes a fluid outlet  340 . Both the fluid inlet  320  and the fluid outlet  340  are at least partially defined by the inner duct  310  which is an inner wall of the body  30  and extends within and along the body. A fluid flow path  300  extends within the inner duct  310  from the fluid inlet  320  to the fluid outlet  340 . At the first end  32  of the body  30 , a side wall  350  extends between the outer wall  360  and the inner duct  310 . This side wall  350  at least partially defines the fluid inlet  320 . The primary fluid outlet  440  is annular and surrounds the fluid flow path. 
         [0049]    A PCB  75  including the control electronics for the hairdryer is located in the body  30  near the side wall  350  and fluid inlet  320 . The PCB  75  is ring shaped and extends round the inner duct  310  between the inner duct  310  and the outer wall  360 . The PCB  75  is in fluid communication with the primary fluid flow path  400 . The PCB  75  extends about the fluid flow path  300  and is isolated from the fluid flow path  300  by the inner duct  310 . 
         [0050]    The PCB  75  controls parameters such as the temperature of the heater  80  and the speed of rotation of the fan unit  70 . Internal wiring (not shown) electrically connects the PCB  75  to the heater  80  and the fan unit  70  and the cable  50 . Control buttons  62 ,  64  are provided and connected to the PCB  75  to enable a user to select from a range of temperature settings and flow rates for example. 
         [0051]    Downstream of the PCB  75 , is the heater  80  and a PCB baffle  700  is provided between the PCB  75  and the heater  80 . The PCB baffle provides thermal protection for the PCB  75  when the heater  80  switched on amongst other things. 
         [0052]    In use, fluid is drawn into the primary fluid flow path  400  by the action of the fan unit  70 , is optionally heated by the heater  80  and exits from the primary fluid outlet  440 . This processed flow causes fluid to be entrained into the fluid flow path  300  at the fluid inlet  320 . The fluid combines with the processed flow at the second end  34  of the body. In the example shown in  FIG. 2 , the processed flow exits the primary fluid outlet  440  and the hairdryer as an annular flow which surrounds the entrained flow that exits from the hairdryer via the fluid outlet  340 . Thus fluid that is processed by the fan unit and heater is augmented by the entrained flow. 
         [0053]      FIG. 4  shows, the heater  80  having a wall  180  which surrounds the heater element  82  and extends around the external periphery of the heater element  82  providing some thermal protection to the outer wall  360  of the body  30  of the hairdryer  10 . The heater element  82  is supported by a scaffold consisting of an inner tube  84  and a plurality of supporting struts  86  which extend radially between the inner tube  84  and the wall  180  and around which the heater element  82  is wound. 
         [0054]    In the event of a blockage either to the fluid inlet  40  or the fluid outlet  440  of the hairdryer  10 , the heater element  82  could overheat as fluid flow over the heater element  82  would be restricted. To prevent this, a number of safety features are provided. 
         [0055]    Referring now to  FIGS. 3, 4, 5, 6   a  and  6   b  a thermistor  220  is retained with respect to a housing  230 . The housing  230  has a base  232  and two arms  234 ,  236  that extend from the base  232 . The thermistor  220  is supported at each end by one of the two arms  234 ,  236 . Electrical wiring  222  that connects the thermistor to a heater control circuit (not shown) is routed through the two arms  234 ,  236  and out of the base  232  to a connector  224  which connects to the PCB  75 . 
         [0056]    In order that the thermistor  220  is reliably positioned with respect to the inner wall  260 , the housing  230  forms part of the inner wall  260 . The housing  230  and inner wall  260  are provided with cooperating features that indicate when the correct position is reached. The inner wall  260  has an aperture  270  into which the housing  230  is inserted. The aperture  270  is defined by a wall  274  which contains a recess  276 . An external surface of the aperture  270  is defined by a flange  272  which extends, in this example around three sides of the aperture  270 . 
         [0057]    The base  230  includes a lip  242  which extends, in this case, around three sides of the base  230 . The lip  242  is designed to engage with the flange  272 . The fourth side of the aperture  270  is defined by a wall  278  that extends orthogonally from the flange  272  thus, the housing  230  can only be inserted into the aperture  270  in one orientation. 
         [0058]    The housing  230  includes a strut  238  which extends from the base  232  between the two arms  234 ,  236 . This strut  238  includes a stop feature, in this case a protrusion  240 . The protrusion  240  is positioned such that when the housing  230  is correctly located with respect to the inner wall  260  the protrusion  240  engages with the recess  276  provided in the wall  274  of the aperture  270 . 
         [0059]    The thermistor  220  has a resistance which changes with temperature so is used to provide a feedback of the actual exit temperature of the heater  80 . Along with the user selected heat and power levels, other factors such as the state of the filter i.e. how dirty the filter is will affect the actual temperature downstream of the heater  80 . The thermistor  220  is positioned within the fluid flow path that exits from the heater  80  and is suspended in the fluid flow path. This is beneficial as the thermistor  220  is open to the fluid flowing past rather than being shielded by a part of the heater structure. 
         [0060]    In order that the thermistor  220  can be reliably and repeatedly positioned within the fluid flow path  400  and with respect to the heater  80 , the inner wall  260  engages with the heater  80 . The inner wall  260  has a pair of lips  262 ,  264  that extend towards the heater  80  and into which the outer wall  180  of the heater  80  is inserted. A radially inner surface  260   a  of the inner wall  260  directs the fluid that exits the heater  80  towards the fluid outlet  440 . 
         [0061]    The radially outer lip  262 , extends over the outer surface  180   a  of the wall  180  and includes a pair of recesses or cut-outs  266 ,  268  for accommodating the wiring  222 . Downstream of the pair of recesses or cut-outs  266 ,  268  an aperture  270  is provided in the inner wall  260 . 
         [0062]    Thus, the housing  230  is reliably positioned with respect to the inner wall  260  and the inner wall  260  is repeatedly positioned with respect to the heater  80 , providing a reliable positioning of the thermistor  220  within the fluid flow path  400  for measurement of the temperature of fluid flowing downstream of the heater  80 . 
         [0063]    The wiring  222  is additionally supported by the PCB baffle  700  via a resilient clip  720  which extends over a recess  722  located at the downstream end of the PCB baffle  700 . The wiring  222  is pushed passed and under the resilient clip  720  into the recess  722  where it remains unless pushed back out. 
         [0064]    The pair of recesses or cut-outs  266 ,  268  in the inner wall  260  provide a channel for the wiring  222 , in which the wiring  222  is at least partially recessed as the wiring  222  travels across from the outer wall  180  of the heater  80  into the housing  230  for the thermistor  220 . This reduces the amount of space required to accommodate the wires and provides some protection when the heater is assembled into the hairdryer. 
         [0065]    The invention has been described in detail with respect to a hairdryer however, it is applicable to any appliance that draws in a fluid and directs the outflow of that fluid from the appliance. 
         [0066]    The fluid that flows through the appliance is generally air, but may be a different combination of gases or gas and can include additives to improve performance of the appliance or the impact the appliance has on an object the output is directed at for example, hair and the styling of that hair. 
         [0067]    The invention is not limited to the detailed description given above. Variations will be apparent to the person skilled in the art. In particular, the heater may be a conventional heater which is trapezoid in shape and wound around a frame formed into a cross shape.