Abstract:
A handheld device comprising a motor for generating an airflow through the device, the motor including: a frame for supporting a rotor assembly and a stator assembly, the frame including an inner wall and an outer wall and a plurality of diffuser vanes extending between the inner wall and outer wall; a rotor assembly including a shaft, a magnet, a bearing assembly and an impeller; and a stator assembly including a bobbin, a stator core and a winding wound around the bobbin; the frame being formed of zinc and the impeller being formed of aluminium.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of United Kingdom Application No. 1521893.6, filed Dec. 11, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a handheld product comprising a motor. 
       BACKGROUND OF THE INVENTION 
       [0003]    When developing a handheld product, it is important to consider a number of factors that will affect the end-user. For example, the size and weight of the product must be kept down in order that a user is able to handle the product easily, and that the product does not cause discomfort to the user during use. Another important consideration is that of noise. It is preferable that a handheld product does not produce a level of noise that is unpleasant and/or uncomfortable during use. What is more, excessive noise could potentially be damaging to a user&#39;s hearing if the product is used regularly over a long period of time. It is often the case that additional soundproofing, for example foam, is included in a product in order to maintain an acceptable level of noise generated by the product. Alternatively, the motor can be run at a lower power to reduce the level of noise that it generates. Of course, neither of these solutions are particularly desirable. Additional components or materials such as foam will increase the cost of the product, and running the motor at a lower power will negatively affect the performance of the product. 
         [0004]    In handheld products which contain motors, it is often the motor that contributes the most towards the weight of the overall product and also towards the noise of the product during use. In smaller, handheld products, it is usual for many components of the motor to be formed of plastics which are more lightweight than other alternative materials. 
       SUMMARY OF THE INVENTION 
       [0005]    Aspects of this invention provide a handheld product comprising a motor for generating an airflow through the product, the motor comprising: a frame for supporting a rotor assembly and a stator assembly, the frame comprising an inner wall and an outer wall and a plurality of diffuser vanes extending between the inner wall and outer wall; a rotor assembly comprising a shaft, a magnet, a bearing assembly and an impeller; and a stator assembly comprising a bobbin, a stator core and a winding wound round the bobbin; the frame being formed of zinc and the impeller being formed of aluminium. 
         [0006]    As a result, the frame, being formed of zinc which is an acoustically dull material, is able to absorb some of the frequencies generated by the motor during use, and in particular the acoustic frequencies. This reduces the level of noise from the motor, and in turn reduces the overall noise generated by the handheld product during use. What is more, by forming the impeller from aluminium, which is an extremely light and strong material, this helps to counteract the additional weight included into the motor due to the use of zinc to form the frame. Therefore there is a synergistic effect in the use of zinc in the frame and aluminium in the impeller. The combination of the aluminium impeller and the zinc frame affords the motor improved acoustic characteristics, but without compromising the overall weight of the motor. Therefore, a handheld product can be achieved that is quieter during use, but without a significant increase to the weight of the overall product. 
         [0007]    The magnet and the impeller may be fixed to the shaft either side of the bearing assembly. This allows the rotor assembly to be evenly balanced, and reduces the forces acting on the bearing assembly during use. This can extend the life of the motor. 
         [0008]    The impeller may be an axial impeller. The frame may be formed from zinc by one or a combination of die-casting and machining. The outer wall of the frame may be substantially cylindrical and may have a substantially uniform internal diameter. 
         [0009]    The bearing assembly may be mounted within the inner wall of the frame. This allows the inner wall to act as a protective sleeve for the bearing assembly. As such, no additional sleeve is required, and so the cost, weight and size of the motor can be reduced. 
         [0010]    The impeller may be formed of machined aluminium, and may comprise a plurality of blades positioned radially around an inner hub. The inner hub of the impeller may comprises a recess. Accordingly, the weight of the impeller can be further reduced, and as such further counteracting the additional weight caused by the zinc frame. 
         [0011]    The impeller may comprise 13 blades. As such, the blades of the impeller will generate a frequency during use that is high enough to be outside the typical hearing range of a human. Accordingly, the acoustic impact of the motor, and therefore the overall product, can be reduced. 
         [0012]    During use, the rotor may spin at a speed of between 75 and 110 krpm to generate airflow through the product. This generates the desired level of air flow through the product, but exerts large forces on the impeller. However, being made of aluminium, the impeller is capable of withstanding these large forces. 
         [0013]    The handheld product may be a hair care appliance, and may be one of a hair dryer, or a hot styling brush. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    In order that the present invention may be more readily understood, embodiments of the invention will now be described, by way of example, with reference to the following accompanying drawings, in which: 
           [0015]      FIG. 1  is a handheld product in the form of a hair dryer; 
           [0016]      FIG. 2  is a cross section through the hair dryer of  FIG. 1 ; 
           [0017]      FIG. 3  is an exploded perspective view of a motor; 
           [0018]      FIG. 4  shows a cross section through a frame of the motor of  FIG. 3 ; 
           [0019]      FIG. 5  shows a cross section through a rotor assembly of the motor of  FIG. 3 ; 
           [0020]      FIG. 6  is an axial impeller; and 
           [0021]      FIG. 7  shows a cross section through a partly assembled motor such as that shown in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIGS. 1 and 2  show a handheld product, represented by hair dryer  1 .  FIG. 2  is a schematic illustration of a cross section through the hair dryer  1 . The hair dryer  1  has a body  2  through which air is expelled, and a handle  3  attached to the body  2  by which a user can hold the hair dryer  1  as shown in  FIG. 2 . The handle  3  comprises an air intake  4  at an end of the handle  3  opposite the body  2 . A motor  5  is located within the handle  3  such that it is positioned next to, or at least close to, the air intake  4 . A filter or other filtering means (not shown) may be provided at the air intake  4 , or between the air intake  4  and the motor  5 , to prevent foreign objects which may be entrained in the airflow, such as hair or dust, from entering the motor  5 . 
         [0023]    During use, the motor  5  generates an airflow through the hair dryer  1 . The motor  5  draws air into the handle  3  through the air intake  4 . Air then passes through the motor  5  and from the handle  3  into the body  2  where is directed towards an air outlet  6 . A heater (not shown), for example in the form of one or more heating elements, may be provided in the hair dryer  1  to heat the air prior to it being expelled from the air outlet  6 . 
         [0024]    A hair dryer  1  is shown as an example in  FIGS. 1 and 2 , however the motor  5  could be used in other handheld products that require the generation of an airflow. For example, the motor  5  could be included in a different hair care appliance: for instance a hot styling brush. 
         [0025]      FIG. 3  is an exploded perspective view of the motor  5 . The motor  5  comprises a frame  10 , a rotor assembly  20  and a stator assembly  40 . A cross section through the frame  10  is shown in  FIG. 4 . The frame  10  comprises an inner wall  11  and an outer wall  12 . A number of diffuser vanes  13  extend between the inner wall  11  and the outer wall  12 . The frame  10  is formed of zinc and can be formed, for example, by machining or die-casting, or a combination of both machining and die-casting. Zinc is an acoustically dull material and so the frame  10  is able to effectively absorb acoustic frequencies generated by the motor  5  during use. The zinc frame  10  therefore acts to reduce the overall level of noise generated by the product  1  during use. 
         [0026]    The rotor assembly  20  comprises a shaft  21 , a magnet  22 , a bearing assembly  23  and an impeller  24 . A cross-section through the rotor assembly  20  is shown in  FIG. 5 . The magnet  22 , bearing assembly  23  and impeller  24  are all fixed directly to the shaft  21  by one or a combination of an interference fit and adhesive. The magnet  22  is a bonded permanent magnet of the sort typically used in permanent magnet brushless motors. In the example shown, the magnet  22  is a four-pole permanent magnet. The bearing assembly  23  comprises a pair of bearings  25   a ,  25   b  and a spring  26  separating the bearings  25   a ,  25   b . The spring  26  acts to pre-load each of the outer races of the bearings  25   a ,  25   b  to reduce wear of the bearings during use. Once the rotor assembly  20  is assembled into the frame  10 , the inner wall  11  of the frame  10  acts as a protective sleeve around the bearing assembly  23 . The outer races of the bearings  25  are fixed to the inside circumference of the inner wall  11  by adhesive. 
         [0027]    The impeller  24  shown in the Figures is an axial impeller with a plurality of blades  27  spaced circumferentially around, and extending radially out from, a central hub  28 . During use, as each blade  27  spins, it creates sound waves at a specific frequency. It is therefore possible to design the impeller in such a way as to reduce its acoustic impact. The impeller  24  shown in  FIGS. 3 and 5  comprises eleven blades. However, the number of blades  27  may differ according to the acoustic requirements of the motor  5  and/or handheld product. For example, an impeller  30  with thirteen blades  27  is shown in  FIG. 6 . During use, due to the higher number of smaller blades  27 , the impeller  30  of  FIG. 6  may generate an acoustic tone that has a higher frequency than the impeller  24  of  FIG. 3  that has only eleven blades  27 . At the expected operating speeds for the motor  5 , the frequency of the tone generated by an impeller  30  with thirteen blades  27  is high enough so as to be outside the typical hearing range of a human. This reduces the acoustic impact of the motor  5  and goes even further to reduce the overall noise generated by the product, i.e. the hair dryer  1 , during use. 
         [0028]    The impeller  24 ,  30  is formed by machining aluminium. Aluminium is a very light material and therefore by using it to form the impeller  24 ,  30  this helps to counteract some of the additional weight included in the motor  5  by using zinc to create the frame  10 . When used in a handheld product such as the hair dryer  1  of  FIGS. 1 and 2 , or another hair care product, the motor  5  will typically be run at rotational speeds of around 75 to 110 krpm. The magnitude of the forces acting on the impeller  24 ,  30  at these high speeds are very great. Thankfully, despite being light, aluminium is also very strong and so the impeller  24 ,  30  is capable of withstanding the large forces subjected to it when it rotates at high speed. 
         [0029]      FIG. 5  shows that the hub  28  of the impeller  24  comprises a recess  29  in the downstream side of the hub. By having a recess  29 , this further decreases the weight of the impeller  24 ,  30 , which counteracts even more of the weight added by using zinc to form the frame  10 . In addition, the recess  29  is annular and provides a cavity into which an axially extending portion or protrusion of the inner wall of the frame can extend. This creates a labyrinth seal inside the hub  28  of the impeller  24  which prevents foreign objects, such as hair and dust, from entering into the bearing assembly  23  which could damage the rotor assembly and significantly reduce the lifetime of the motor. The labyrinth seal can be seen in  FIG. 7  which shows a cross section through the assembled frame  10  and rotor assembly  20 . The labyrinth seal is highlighted at area S.  FIG. 7  shows how the inner wall  11  of the frame  10  acts as a protective sleeve around the bearing assembly  23 , as previously described. 
         [0030]    Whilst particular embodiments have thus far been described, it will be understood that various modifications may be made without departing from the scope of the invention as defined by the claims.