Abstract:
A food processor has a container, a working piece for processing food material in the container, and a motor assembly for driving the working piece. The motor assembly includes an electric motor and a speed reduction gear unit connected between the motor and the working piece. The speed reduction gear unit includes a damper for isolating the motor from vibrations from the working piece.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 201110289057.4 filed in The People&#39;s Republic of China on Sep. 26, 2011. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a food processor and in particular, to a motor assembly for the food processor. 
       BACKGROUND OF THE INVENTION 
       [0003]    US2003/0145737A1 discloses a bread maker which includes a casing, a mixing rod, a baking oven, a bread making chamber unit, and an electrical heating tube. The mixing rod is driven by a motor unit. The motor unit includes an alternating current motor and a speed reduction gear unit. The speed reduction gear unit comprises a transmission gear and a gear case. The transmission gear is engaged with a gear shaft of the motor. The power of the motor is transmitted to a rotating fork which in turn rotates the mixing rod. The above bread maker has some disadvantages. Firstly, the height of the bread maker is relatively large. Secondly, the vibration on the mixing rod will be transmitted to the shaft of the motor, which brings negative influence on the performance of the motor. 
       SUMMARY OF THE INVENTION 
       [0004]    In one aspect thereof, the present invention provides a motor assembly, comprising an electric motor and a speed reduction gear unit driven by the motor, the speed reduction gear unit comprising a main shaft and an output unit, wherein the main shaft comprises a metal body and an thermal insulating portion formed on the metal body, the output unit being at least partly sleeved on the thermal insulating portion to prevent heat on the output unit from being transmitted to the metal body. 
         [0005]    Preferably, the thermal insulating portion is over-molded on the metal body. 
         [0006]    Preferably, the output unit comprises a first member and a second member engaged with the first member, the second member being made of metal and sleeved on the thermal insulating portion. 
         [0007]    Preferably, the first member is made of low heat resistant material. 
         [0008]    Preferably, a sealing ring is received inside the first member and tightly sleeved on the main shaft. 
         [0009]    In a second aspect thereof, the present invention provides a food processor, comprising: a container; a working piece for processing food material in the container; and a motor assembly for driving the working piece, the motor assembly comprising an electric motor and a speed reduction gear unit connected between the motor and the working piece; wherein the speed reduction gear unit comprises a damper for isolating the motor from vibrations from the working piece. 
         [0010]    Preferably, the speed reduction gear unit further comprises a stationary main shaft, and a toothed wheel and an output unit which are rotatably sleeved on the main shaft, the damper being axially arranged between the toothed wheel and the output unit and transmitting the rotation of the toothed wheel to the output unit. 
         [0011]    Preferably, the motor has a worm shaft and the toothed wheel is engaged with the worm shaft. 
         [0012]    Preferably, the main shaft comprises a metal body and a thermal insulating portion on the metal body, the output unit being at least partly sleeved on the thermal insulating portion. 
         [0013]    Preferably, the output unit comprises a first member and a second member separately formed and engaged with the first member, the second member being made of metal and sleeved on the thermal insulating portion, and the toothed wheel is made of low heat resistant material. 
         [0014]    Preferably, the first member is coupled to the damper. 
         [0015]    Preferably, a sealing ring is received inside the first member and tightly sleeved on the main shaft. 
         [0016]    Preferably, a plurality of small protrusions project from one axial end surface of the damper facing the output unit to contact an adjacent axial end surface of the output unit. 
         [0017]    Preferably, a sealing ring is received inside the first member and tightly sleeved on the main shaft. 
         [0018]    In a third aspect thereof, the present invention provides a bread maker, comprising: a casing; a container arranged in the casing; a baking chamber with a heater for heating the container; a kneading tool rotatably disposed in the container for kneading bread material; and a motor assembly comprising an electric motor and a speed reduction gear unit connected between the motor and the kneading tool; wherein the motor has a worm shaft, and the speed reduction gear unit has a worm wheel and a main shaft, the worm wheel being sleeved on the main shaft and engaged with the worm shaft. 
         [0019]    Preferably, the kneading tool is coaxial with the main shaft. 
         [0020]    Preferably, the speed reduction gear unit comprises a damper for isolating the motor from vibrations from the kneading tool. 
         [0021]    Preferably, the speed reduction gear unit further comprises an output unit, wherein the main shaft is stationary and the worm wheel and the output unit are rotatably sleeved on the main shaft, and the damper is disposed between the worm wheel and the output unit to transfer the rotation of the worm wheel to the output unit. 
         [0022]    Preferably, the main shaft comprises a metal body and a thermal insulating portion formed on the metal body, the output unit being at least partly sleeved on the thermal insulating portion. 
         [0023]    Preferably, the output unit comprises a first member and a second member separately formed and engaged with the first member, the second member being made of metal and sleeved on the thermal insulating portion, and the worm wheel is made of low heat resistant material, and the first member is coupled to the worm wheel via the damper. 
         [0024]    Preferably, a plurality of small protrusions project from one axial end surface of the damper facing the output unit to contact an adjacent axial end surface of the output unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Preferred embodiments of the invention will now be described, by way of example only, with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labeled with a same reference numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below. 
           [0026]      FIG. 1  is a partially sectioned view of a bread maker in accordance with a preferred embodiment of the present invention; 
           [0027]      FIG. 2  is a view of a motor assembly, being a part of the bread maker of  FIG. 1 ; 
           [0028]      FIG. 3  is an exploded view of a speed reduction gear unit being a part of the motor assembly of  FIG. 2 ; 
           [0029]      FIG. 4  is a sectional view of the motor assembly of  FIG. 2 ; and 
           [0030]      FIG. 5  is another exploded view of the speed reduction gear unit of  FIG. 3 , with a gearbox housing and a gearbox cover omitted. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]      FIG. 1  illustrates a bread maker  10  in accordance with a preferred embodiment of the present invention. The bread maker  10  is shown partially sectioned and includes a casing  12 , a lid (not shown), a container  14  arranged in the casing  12 , a baking chamber  16 , a heater (not shown) arranged with the baking chamber  16  for heating the container  14 , a kneading tool  18  rotatably disposed in the container  14  for kneading bread material, and a motor assembly  20  for driving the kneading tool  18 . 
         [0032]    The motor assembly  20  includes an electric motor  22  and a speed reduction gear unit  30 . Preferably, the electric motor  22  is a high voltage direct current motor. 
         [0033]    The reduction gear unit  30  includes a gearbox housing  32 , a gearbox cover  34 , a worm wheel  40 , an output unit  50 , a damper  60  and a main shaft  70 . The gearbox housing  32  is fixed to the housing  24  of the motor  22  and has a circular recess  36 . The gearbox cover  34  is fixed to the gearbox housing  32  via screws  38 . 
         [0034]    The worm wheel  40  is rotatably received in the recess  36  of the gearbox housing  32  and includes a circular base wall  41  with a central hole, a annular flange  42  axially extending from the outer periphery of the base wall  41 , and a hub  43 . The hub  43  has a shaft sleeve portion  44  coaxially extending from the inner surface of the central hole of the base wall  41  and an outer ring  45  surrounding the shaft sleeve portion  44 . A plurality of teeth are formed on the outer surface of the flange  42  to engage with a worm shaft  26  of the motor  22  such that the motor  22  drives the worm wheel  40  to rotate at a speed lower than the speed of the worm shaft  26 . A plurality of ribs  46  radially extend between the inner surface of the flange  42  and the outer surface of the outer ring  45  of the hub  43 . 
         [0035]    The output unit  50  includes a first member  51  and a second member  52 . The first member  51  has a circular disc  53  with a central hole. The circular disc  53  is received inside the flange  42  of the worm wheel  40 . An inner toothed ring  54  coaxially and integrally extends from one end surface of the circular disc  53  away from the base wall  41  of the worm wheel  40 . The second member  52  includes an outer toothed ring  55  and an output coupling  56  coaxially and integrally extending from one end surface of the outer toothed ring  55  away from the circular disc  53 . The outer toothed ring  55  is received in and engaged with the inner tooth ring  54  such that the second member  52  is able to rotate with the first member  51 . 
         [0036]    The damper  60  is made of resiliently deformable material such as rubber and is axially disposed between the worm wheel  40  and the output unit  50 . The damper  60  has a circular ring configuration and includes a plurality of main parts  61  spaced in the circumferential direction and a plurality of openings  62  formed in the main parts  61 . Inner radial ends of adjacent main parts  61  are connected to each other via a bridge  63 . The damper  60  is arranged between the outer surface of the outer ring  45  of the hub  43  and the inner surface of the flange  42  with each main part  61  being arranged between adjacent ribs  46  of the worm wheel  40  such that the damper  60  rotates with the worm wheel  40 . A plurality of pins  57  project from the axial end surface of the circular disc  53  remote from the inner toothed ring  54  and are disposed in the openings  62  in the main parts  61  such that rotation of the damper  60  is able to cause rotation of the circular disc  53 . Preferably, a plurality of small protrusions  64  project from axial end surfaces of the main parts  61  facing the circular disc  53  such that the contact area between the damper  60  and the circular disc  53  is reduced to balance the noise and vibration between them. 
         [0037]    The main shaft  70  is perpendicular to the worm shaft  26  of the motor  22  and fixed to the gearbox housing  32 . Preferably, the gearbox housing  32  is over-molded on the main shaft. The worm wheel  40 , the first member  51 , and the second member  52  are coaxial with and rotatably sleeved on the main shaft  70 . The inner toothed ring  54  of the first member  51  and the second member  52  pass through a through hole of the gearbox cover  34 . An intermediate coupling  19  directly or indirectly connected with the kneading tool  18  is coupled to the output coupling  56  of the second member  52  to transmit the rotation of the reduction gear unit  30  to the kneading tool  18 . 
         [0038]    Preferably, the worm wheel  40  is made of low heat resistant material such as resin. Preferably, the first member  51  is made of a resin which can withstand higher temperatures. The second member  52  is made of metal. The main shaft  70  comprises a metal body  72  and a thermal insulating portion  74  formed on one end of the metal body  72  adjacent the output unit  50 . The first member  51  and the second member  52  are sleeved on the thermal insulating portion  74 . Preferably, the thermal insulating portion  74  is made of heat resistant plastic, for example, a thermosetting plastic and over-molded on the metal body  72 . An aperture  76  for discharging the gas generated during the forming of the thermal insulation portion  74  is formed in the thermal insulating portion  74 . A sealing ring  37  is received inside the circular disc  53  and tightly sleeved on the main shaft  70 . 
         [0039]    In this embodiment, the cost and weight of the motor assembly  20  are relatively low as the worm wheel  40  and the first member  51  are made of resin. Moreover, the worm wheel  40 , which is of low heat resistant material, will not be negatively influenced by heat from the kneading tool  18  as heat transmitted to the second member  52  from the kneading tool  18  via the intermediate coupling  19  is not transmitted to the worm wheel  40  because of the thermal insulating portion  74 . Thirdly, the motor  22  is isolated from vibrations generated by the kneading tool  18  as the vibrations can be absorbed by the damper  60 . Fourthly, the motor assembly  20  has a compact structure in the axial direction of the main shaft  70  such that the height of the bread maker  10  can be reduced. 
         [0040]    A low heat resistance material is generally considered to be a material which can only withstand temperatures up to about 100° C. As an example, the preferred material of the worm wheel  40  is polyoxymethylene (POM), which can withstand a maximum temperature of 75° C. The preferred material of the first member  51  and the thermal insulating portion  74 , is glass fiber filled Nylon 66 (PA66+GF) or glass fiber filled polyphthal amide (PPA+GF), which can withstand 250° C. 
         [0041]    In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items. 
         [0042]    Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow. 
         [0043]    For example, it should be understood that the motor assembly  20  may be applied to other types of food processors besides bread makers.