Abstract:
A dishwasher which uses a high voltage DC motor to drive a pump. The dishwasher cleans dishes and cooking and eating utensils by the use of a high pressure water spray driven by an electric pump which circulates water. The DC motor may have a built in motor controller to allow the motor to have a soft start, multiple speeds, smooth ramping between speeds and load control. This allows for an energy efficient system and noise prevention.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from provisional U.S. Application 60/646,536, filed Jan. 25, 2005, which is hereby incorporated by reference. This provisional patent application claims no priority. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to dishwashers with pumps driven by electric motors and more specifically to dishwashers having pumps driven by high voltage DC motors. 
     2. Description Of The Background 
     Dishwashers have become a common household appliance. As is well known, implements and utensils used for cooking and eating may be placed inside a special waterproof cabinet so that hot soapy water can be sprayed under high, but controlled, pressure to remove food particles, grease, and other debris from the items placed in the dishwasher. The items then become clean so that they may be reused. 
     Such dishwashers normally include a pump to provide the water spray with a controlled pressure. The water is recirculated by using a coarse filter system. The pumps are normally driven by an electric motor. Currently, most dishwashers use an induction motor, such as a permanent split capacitor motor, to drive the pump, because this type of motor has a reliable construction. 
     While this type of induction motor has been commonly used for many years, there remain some disadvantages to such a motor. First, in view of high energy costs, the efficiency of the motor is an important consideration. This is especially true as dishwashers are used more extensively. Another disadvantage of the induction motor is the audible noise created. Consumers prefer that the dishwasher create as little noise as possible, especially when the dishwasher is run at night. 
     SUMMARY OF THE INVENTION 
     Thus, the present invention provides a dishwasher having a high voltage DC motor in order to avoid the disadvantages of prior art motors. 
     The present invention provides an energy efficient dishwasher. 
     The present invention further provides a dishwasher which has low audible noise. 
     Furthermore, the present invention provides a high efficiency dishwasher having low audible noise. 
     The present invention further provides a dishwasher having a high voltage permanent magnet direct current motor for driving a main water circulation pump. 
     The present invention still further provides a dishwasher with a high voltage permanent magnet direct current motor which is energy efficient and has low noise. 
     These and other advantages are obtained by providing a dishwasher using a high voltage permanent magnet direct current motor for driving a main water circulation pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of a dishwasher according to the present invention; 
         FIG. 2  is a perspective view of a motor for the dishwasher of  FIG. 1 ; 
         FIG. 3  is a view of an alternative motor for the dishwasher of  FIG. 1 : 
         FIG. 4  is an exploded view of the motor of  FIG. 3 ; 
         FIG. 5  is a sectional view of the motor of  FIG. 3 ; 
         FIG. 6  is a view of a further alternative motor of the dishwasher of  FIG. 1  showing a built-in controller. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a dishwasher  10  with a front door  11  open to view various interior features such as the filter  12 , the sump  13 , water wands,  14 ,  15  detergent dispenser  16  and wire racks  17 ,  18  (only partially shown to give a general impression.) The operation of the dishwasher is of a standard technique and will not be described in detail except to explain that water entering the sump is coarsely filtered by the filter and repeatedly sprayed through the water wands onto dishes and other objects to clean them. 
     Shown in hidden outline is the body of the sump  13  in which the water collects after being filtered and an electric pump  19  for circulating the water within the dishwasher from the sump  13  to the wands  14 ,  15 . Also provided but not shown are water fittings, drainage system which may include a separate drain pump, electrical supply and a controller for controlling operation and timing of the function performed by the dishwasher. 
     The sump  13  is similar to a bowl for collecting the water from the inside of the washing cavity  20  and has an outlet connected to an inlet of the pump  19 . The pump  19  has an impeller driven within a pump chamber by an electric motor. The pump may include a macerator for reducing the size of large food particles. 
       FIG. 2  shows a first embodiment of the electric pump  19  used in the dishwasher  10 . The pump includes a pump section  22  driven by an electric motor  21 .  FIG. 2  does not show the fan cover which has been removed. The motor is a single speed, high voltage permanent magnet direct current (HVDC) motor. The motor has a 2-pole permanent magnet stator and a 24 pole wound rotor. The motor has a single speed preferably operating at 3600 rpm or higher and being connected to the mains electrical supply through a rectifier circuit, but without a transformer. Thus, the motor voltage is 120 volts DC when used in a U.S. domestic dishwasher. Preferably, the motor has an expected life of 5,000 hours of operation. The motor has an efficiency of more than 65% and preferably 70% or more. 
     It would also be possible that the single speed motor of the first embodiment shown in  FIG. 2  could be operated in the two speed mode by selectively supplying current to the motor through a half bridge rectifier or a full wave rectifier. 
     The motor is shown attached to the pump section  22 , although only the pump cover  23  is clearly visible. The other end of the motor is normally closed by a fan cover which is removed in  FIG. 2  to show a cooling fan  24  attached to an end of the motor shaft  25 . Also visible is a motor end bracket or end cap  26  supporting a shaft bearing (not visible), brush gear  27  in the form of a pair of cage brushes and a motor terminal connector  28  for connecting the motor to an electrical power source. A second end bracket or end cap  29  is located at the opposite end of the motor and supports a second bearing for the motor shaft. This end cap also forms part of the pump section, dividing the pump chamber from the motor and supports seals for preventing water entering the motor along the motor shaft. 
     The second embodiment of the motor of the present invention is shown in  FIGS. 3 ,  4  and  5 . The construction of the pump and motor is similar to that of  FIG. 2  with the exception that the first end bracket  26  includes a receptacle  52  for the smoothing capacitor  45 , a recess  53  for a thermal cut out switch and a compartment  54  for a full wave bridge rectifier. By using this arrangement, the motor can be connected to a standard AC electrical current which is then converted to DC current by way of the bridge rectifier which is part of the motor section. Thus, the motor can be used with no change to the control module in the dishwasher when it replaces an AC motor. Of course, it would also be possible to modify the dishwasher controller to provide the required DC power to operate in the desired fashion. 
       FIG. 3  is a perspective view of the electric pump with the motor fan cover removed and with the pump cover removed.  FIG. 4  is an exploded view and  FIG. 5  is a sectional view of the pump of  FIG. 3  with the pump cover removed. Details of the construction of the motor and pump section will now be described. The motor  21  is shown with a pump impeller  30  attached to the motor shaft  25 . Adjacent the impeller  30  is part of the pump chamber forming a backing for the impeller  30  and the impeller volute (not shown). The pump cover  23  also houses the macerator  32  which is a metal disc with two integral radially extending blades which rotate with the shaft  25  within a separate chamber  33  in the pump section  22 . Any large food particles which flow into the macerator chamber will be hit by the rotating blades and broken up into small pieces. This prevents larger food particles from clogging the drain pump at the end of the wash cycle. 
     Adjacent the macerator and forming a wall of the pump chamber is the second end cap  29  of the motor. The motor shaft  25  passes through the end cap  29  with a seal assembly  34  disposed between the shaft  25  and the end cap  29  to keep water and other liquids out of the motor. The end cap  29  also supports a bearing  35  for the motor shaft  25 . 
     Next along the shaft  25  is a wound rotor assembly  36 . The rotor assembly comprises a rotor core of laminated steel construction and a commutator  37 , both mounted on the shaft. Rotor windings are wound around poles of the rotor core and terminated on the commutator. The rotor has  24  poles. The rotor assembly is located in working association with a stator  38  comprising two arcuate ceramic permanent magnets  39  fitted to the inside of a metal ring or housing  40 . Around the housing is a second ring of steel known as a keeper ring or flux ring  41 . 
     At the other end of the housing is the first end cap  26  closing off the housing  40  and supporting the other bearing  42  for the shaft  25 . The shaft  25  extends through the end cap  26  and the fan  24  is attached to the end of the shaft  25  to provide a flow of air within the motor to cool it. A cover  43 , not shown in  FIG. 3 , is also provided to protect the fan and has vents  44  for the flow of the cooling air. The end cap  26  also supports the brush gear  27  and motor terminations  28 . The motor terminations may be lead wires but preferably, as shown, the terminations are terminals  28 . The terminals may be connected directly to the brush gear  27  or via a noise suppression component such as a capacitor  45 . 
     The brush gear comprises two cage brushes  46 . The brushes are of the sintered graphite construction with an embedded shunt and may slide directly in passageways formed in the end cap  26  or the passageways may have a metal, preferably brass, liner  47 . Springs  48 , either coil type or torsion type, urge the brushes  46  into sliding contact with the commutator  37 . The contact face of the brushes  46  preferably have a plurality of ridges so as to contact the commutator  37  at a plurality of points to ensure good contact between the commutator  37  and the brush  46 . The commutator surface is preferably polished to provide a smooth rubbing surface between the brush and the commutator to reduce audible noise created by the brushes sliding over the commutator surface. 
     A speed or position sensor may be provided by adding a small ring magnet  49  rotating with the shaft and locating a sensor, such as a Hall sensor  50 , in association with the ring magnet  49  to sense changes in the magnetic field of the ring magnet  49  as the shaft  25  turns. The output signals of magnetic sensors, especially Hall sensors, can be considered as a binary signal. A twelve pole output signal means that the sensor magnet has twelve poles (six pairs of M-S poles), thus producing six or twelve pulses per revolution, depending on the sensor type. The greater the number of poles, the better the resolution of the position or speed sensor. 
     Although a Hall sensor feedback device is used in this embodiment, other feedback devices, such as an optical sensor may be used instead to provide a speed signal to the motor controller. 
     The end caps  26 ,  29  are connected to the stator  38  by locking fingers  51  formed integrally with the stator housing  40 , being bent or otherwise deformed over ridges or projections or steps on the end caps to hold the end caps in place. The fingers preferably extend in a circumferential direction of the stator housing  40 . Flanges  52  or stops on the end caps  26 ,  29  allow the end caps to be inserted into the stator housing  40  to a predetermined axial depth. In addition or in place of the locking fingers, screws may be provided which extend through the stator from one end cap to the other to securely clamp the end caps to the stator. The screws would pass through the circumferential gaps between the two magnets  39 . 
     To reduce exposure of the motor shaft to chemical erosion by the washing chemicals, the motor shaft  25  may include a plastics material cover  56  where the shaft extends within the pump section  22 , covering the shaft from the seal assembly  34  to the impeller and the cover  56  has a molded feature to securely key the impeller  30  to the shaft cover  56 . A screw  57  may be used to secure the impeller  30  to the shaft cover  56  as well or instead of the molded feature of the cover. 
     Also, it can be seen that the motor has a separate socket or set of three terminals  55  which are connected to the speed sensor. The speed sensor is located on the end of the bearing bracket of the first end cap  26 , tucked in underneath the fan  24 . By fitting the magnet to the fan, no additional space is required since it is located in a dead space. It also reduces the number of items to be attached to the shaft. The ring magnet  49  may be fitted to the shaft directly underneath the fan  24  or as a part of the fan  24 . In the cross-section shown in  FIG. 5 , the ring magnet  49  can be seen fixed to an inner surface of the fan  24 , radially inward of the fan blades, therefore effectively not occupying any additional space within the motor. The speed sensor provides feedback to the motor controller allowing the speed of the motor to be controlled. 
     The motor of  FIG. 6 , as an alternative to the motor of  FIG. 2 , is a HVDC motor having a controller  58  built-in and being designed to run at multiple speeds. For example, a simple variation would be a 2 speed motor operable at 2000 rpm and 4000 rpm. The controller  58  would receive signals, either in digital or analog form, from the dishwasher controller to operate at a particular speed. The motor controller then supplies power to the motor to operate the motor at the desired speed. Such control mechanisms allow for the incorporation of special features such as a soft start and smooth change between speeds as well as controlled stopping of the motor. Controlled ramp up of the speed is appreciated to avoid sudden surges in water pressures. Other features which would be possible with the built in controller is a load variable speed control and optional speed/load setting for optimal efficiency and/or noise control. In the motor of  FIG. 6  which is shown in schematic form for simplicity of description, the fan cover  43  has been partially sectioned to show the printed circuit board (PCB)  59  of the motor controller  58 . The fan cover has a plurality of ventilation slots  44  for motor cooling around the periphery of the fan cover  47  and ventilation slots  60  on the end of the cover providing passage of air for cooling of the PCB  59  and its components, thus providing two cooling air flow paths through the fan cover. The two cooling air flow paths may not be completely separate although the PCB  59  can be arranged inside the cover so as to divide the air flow. 
     By using a high voltage DC motor, the energy utilization of the dishwasher is improved. The water circulation pump is the main power consumer of the dishwasher. The PSC motor runs at an efficiency of between 55% to 65% whereas the high voltage DC motor runs at an efficiency of between 65% to 85%. The speed of the motor can be optimized for maximum performance and is not dependent on the frequency of the supply power. The HVDC motor has four to five times higher starting torque and higher torque at lower speeds, meaning that starting can be easier and due to the controller, can be controlled easily to provide a soft start up and smooth ramp up/ramp down between operating speeds to avoid high surge currents. 
     The high starting torque of the HVDC motor is well appreciated for dishwashers which have a fairly high static friction caused by the water seals on the pump shaft and due to the pumps being started under full load. Also, the pumps may be partially blocked by sludge if the machines have not been used for an extended period of time, especially when they have not been properly emptied after the last use. 
     The HVDC motor also provides a quieter dishwasher. Firstly, it does not suffer from the 50/60 Hertz hum which plagues induction motors and which is particularly offensive to normal human hearing. This is appreciated by many users and leads to, at least the perception, of a quieter appliance. 
     The audible noise of the dishwasher increases with the speed of the pump motor. By having greater controllability over the speed of the pump, an even quieter operating mode can be achieved by operating the pump at a lower speed. The cleaning effect can be maintained by operating longer. 
     The HVDC motor also can be made significantly smaller than an equivalent induction motor with the same output power resulting in a smaller, lighter and thus, easier to handle pump/motor unit. 
     The desire for a variable speed comes from the desire for a variable pressure water supply. Varying the speed of the pump is an easy way to achieve this. With a single pump pressure, the cleaning effect is a compromise between delicate objects which can be damaged by high pressure and cooking utensils which require a high pressure to be cleaned properly. The result is often broken delicate crockery and unclean pots and pans. With a variable speed pump, different washing programs can be chosen allowing fine delicate china or even crystal to be cleaned by the same dishwasher that can effectively clean the toughest cooking pans. It also allows shorter cycles by using higher pump speeds and quieter modes by operating at slower pump speeds for longer. By controlling the acceleration as well as the speed, the rate of increase in water pressure can be controlled. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.