Abstract:
A motor assembly, especially for home appliances such as a cleaner, has an electric motor and a cooling system. The motor may be a fractional horsepower universal motor with a stator and a rotor. The cooling system has a cooling pipe thermally coupled to an element of the stator, such as a core of the stator and providing a flow path for a liquid to cool the motor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 201010174457.6 filed in The People&#39;s Republic of China on May 11, 2010. 
     FIELD OF THE INVENTION 
     This invention relates to an electric motor assembly and in particular, to a water cooled electric motor for use in home appliances. The power of the motor is preferably not more than 3,000 watts. Preferably, the electric motor is rated as a fractional horsepower motor. 
     BACKGROUND OF THE INVENTION 
     Traditional small electric motors, especially fractional horsepower motors, are usually air cooled by an axial fan mounted on the rotor shaft to generate a flow of air. Because of the fan, the size of the motor is increased and the efficiency of the motor is decreased. 
     Further more, in specified applications, there is not enough space for a channel or passage within the motor or stator for the air flow, preventing the heat from dissipating quickly. 
     Hence there is a desire for a small size electric motor with improved cooling. 
     SUMMARY OF THE INVENTION 
     This is achieved in the present invention by using a liquid cooling system to cool the stator of the motor. 
     Accordingly, in one aspect thereof, the present invention provides a motor assembly comprising an electric motor and a cooling system, the motor comprising a stator and a rotor rotatably mounted to the stator, wherein the cooling system comprises a cooling pipe thermally coupled to an element of the stator and providing a flow path for a liquid. 
     Preferably, the cooling pipe is at least partially embedded in a stator core of the stator. 
     Preferably, the cooling pipe comprises a plurality of straight pipes and a plurality of bent pipes, the bent pipes interconnecting the straight pipes and the straight pipes extending axially and being at least partly embedded in a core of the stator. 
     Alternatively, the motor assembly comprises a thermally conductive ring member disposed around the stator, and the cooling pipe is disposed inside the ring member. 
     Preferably, the cooling pipe is spirally embedded inside the ring member. 
     Preferably, the motor assembly comprises a tank for storing the liquid and a pump arranged to move the liquid through the cooling pipe. 
     Preferably, the motor assembly further comprises at least one spray nozzle arranged to spray the liquid onto a working area after the liquid has passed through the cooling pipe. 
     Preferably, the motor assembly further comprises an electric heating member arranged to heat the liquid from the cooling pipe to a predetermined temperature before being sprayed from the at least one spray nozzle. 
     Preferably, the liquid is water or water mixed with detergent. 
     Preferably, the working area is a roller brush of a cleaner. 
     Preferably, the rated power of the motor is equal to or less than 3,000 watts. 
     Preferably, the motor is a fractional horsepower universal motor. 
     By implementing the invention, the motor is cooled by the liquid coolant such as water inside a cooling pipe that is thermally coupled to the stator. Thus the size of the motor can be decreased without reducing the power of the motor or the power of the motor increased without increasing the size of the motor. In other words, the power density of the motor can be increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment 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. 
         FIG. 1  is a view of a blower incorporating an electric motor according to a first embodiment of the present invention; 
         FIG. 2  is a partially exploded view of a blower incorporating an electric motor according to a second embodiment of the present invention; 
         FIG. 3  is an assembled view of the blower of  FIG. 2  with a part partially sectioned; and 
         FIG. 4  is a schematic representation of a cleaner incorporating an electric motor according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a motor assembly according to a first embodiment of the present invention. The motor assembly is a blower as used for example in a carpet cleaner or vacuum cleaner. The blower has an electric motor driving an impeller  25  which creates the vacuum for the appliance. The motor is a low power universal motor, preferably no more than 3,000 watts. Optionally, the motor is a fractional horsepower motor. The motor comprises a stator and a rotor  22  rotatably mounted to the stator. The stator comprises stator core  11 , stator windings wound about teeth  12  of the stator core, brush gear disposed at one end of the stator core, and support members such as bearing brackets  13  mounted at respective ends of the stator core for rotatably supporting the rotor. The rotor comprises a shaft  21 , rotor core mounted to the rotor shaft, a commutator  23  fixed to the rotor shaft adjacent to the rotor core, and rotor windings wound about teeth of the rotor core and electrically connected to segments of the commutator. Bearings  14  are mounted to respective support members for supporting the rotor shaft  21 . The load in the form of the impeller  25  is fixed onto one end of the shaft  21 . 
     The motor assembly further comprises a cooling pipe  16 . The cooling pipe  16  comprises a plurality of straight pipes  17  and a plurality of bent pipes  18 . The straight pipes  17  extend axially and are partly embedded in the stator core  11 . The straight pipes  17  are made of thermally conductive material such as aluminum or aluminum alloy. The bent pipes  18  serially connect the straight pipes  17 . The bent pipes  18  are made of flexible material such as rubber. In this embodiment, mounting holes are prefabricated in the stator core laminations. The stator core laminations are then laminated along the straight pipes  17 . The outside diameter of the straight pipes  17  is slightly larger than the inner diameter of the mounting holes. In other words, the straight pipes  17  are preferably a press fit with the mounting holes to improve the thermal conductivity between the stator core  11  and the straight pipes  17 . 
     The cooling pipe  16  is filled with coolant for removing the heat. Preferably, the coolant is water driven by a pump (not shown). The pump may be driven by the motor itself, or driven by another motor. Alternatively, a water tank (not shown) is disposed above the stator core  11  and the inlet of the cooling pipe  16  is connected directly to the water tank. In this arrangement the water flows through the cooling pipe  16  under the influence of gravity. 
     In this embodiment, the motor is cooled by the cooling pipe  16  being embedded directly in the core of the stator. Compared to a traditional motor assembly having an axial fan, the size particularly the axial dimension of the motor assembly according to an embodiment of the invention is decreased. 
       FIG. 2  and  FIG. 3  illustrate another motor assembly according to a second embodiment of the present invention. The motor assembly is shown fitted to a blower similar to the blower of  FIG. 1 . In this embodiment, the cooling pipe  16  is not embedded into the stator core  11 . Instead, the cooling pipe  16  is disposed around the stator core  11  in a thermally conductive way, such that the cooling pipe is thermally coupled to the stator core. Specifically, the motor assembly comprises a thermally conductive ring member forming a cooling jacket  15  made of thermally conductive material such as aluminum. The cooling pipe  16  is spirally embedded inside the jacket  15 . The cooling jacket  15  is mounted around the stator core  11 , with thermally conductive silicone filled between the jacket  15  and the stator core  11 , to improve the thermal connection between the stator core  11  and the jacket  15 . The cooling pipe  16  is made of a thermal conductive material. The jacket  15  and the cooling pipe  16  are preferably formed as one single piece by molding. 
     Alternatively, the cooling pipe  16  is wound about the stator core  11  directly. In another alternative embodiment, the stator core  11  is mounted inside a cylindrical metal housing and the cooling pipe  16  is wound about the metal housing. 
       FIG. 4  is a schematic block diagram representing a motor assembly for a cleaner, especially a floor cleaner or carpet cleaner. The cleaner has a spray system for spraying detergent or a detergent mixture. The motor assembly comprises a motor, a cooling pipe for transferring heat from the motor, a water tank, a pump, an electric heating member, at least one nozzle, at least one sensor, and a control circuit etc. The inlet of the cooling pipe  16  is connected to the water tank  31 . The pump  33  is connected to the outlet of the cooling pipe  16 . 
     In use, the water from the tank  31  flows through the pipe  16  where it is heated by the heat of the stator core  11 . Detergent, as indicated by arrow  32 , is introduced into the water flow to produce a detergent mixture. The pump forces the detergent mixture through the spray nozzle  35 , to spray the detergent mixture onto a working area such as the roller brushes  37  of the cleaner. As is generally known, to maximize the cleaning effect of detergent, the detergent mixture should be within a specific temperature range. Therefore, the electric heating member  38  is disposed between the outlet of the cooling pipes  16  and the nozzles  35 , to heat the detergent mixture to the desired temperature. The sensor senses the temperature of the detergent mixture. The water flow and/or the detergent flow and/or the heating element may be controlled by the control circuit to make sure that the detergent mixture is heated to the desired temperature. 
     In this embodiment, heat from the motor is used to heat the water. In other words, the heat of the motor is reused rather than dissipated to the environment. This reduces the energy required by the heating element to heat the detergent mixture. The solution is particularly useful for applications that require the water to be heated to a specific temperature, whereby the energy used by a secondary heating unit can be reduced by warming the water with waste heat from the motor. For instance, the solution can be used in a coffee machine, soy milk maker, cleaner, etc. 
     The motor shown in the embodiments is a universal motor. However, the motor could be a brushless motor having a stator with a stator core and stator windings, or a PMDC motor with a wound rotor and a permanent magnet stator. Preferably, the motor has a power rating of 3,000 watts or less. Ideally the motor is a fractional horsepower motor. 
     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. 
     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.