Abstract:
Systems and methods for bypassing a centrifugal switch are disclosed. The systems may include a bypass relay operatively connected to the heating element and configured to bypass the centrifugal switch prior to the drum reversing rotational direction, and allow the heating element to remain energized during the drum reversing rotational direction. The centrifugal switch bypass circuit further includes a relay hold circuit operatively connected to the bypass relay and configured to cause the bypass relay to continue bypassing the centrifugal switch during the drum reversing rotational direction. The method may include, once the drum begins reversing the rotational direction, utilizing a bypass relay to bypassing the centrifugal switch. Finally, the method may include utilizing a relay hold circuit to cause the bypass relay to continue bypassing the centrifugal switch during reversal of the rotational direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to U.S. patent application having Ser. No. 12/325,221 titled “Dryer With Reverse Tumble Action” filed Nov. 30, 2008 and U.S. patent application having Ser. No. 12/325,219titled “Dryer With Stationary Drying Cycle” filed Nov. 30, 2008. 
     FIELD OF INVENTION 
     Embodiments of the present invention relate to bypass switches. More specifically, embodiments of the present invention relate to systems and methods for bypassing centrifugal switches found in dryers. 
     BACKGROUND OF THE INVENTION 
     Centrifugal switches are a safety feature that prevents the heating element from operating when the drum is not rotating. Currently, dryers use centrifugal switches to ensure that the heating element does not operate when the drying compartment (i.e. drum) is not rotating. Generally, centrifugal switches used in dryers are normally open and as the drum reaches a minimum rotation speed, the switches are “thrown” to the closed position, thereby completing the circuit and allowed the heating element to receive power. Should the drum stop rotating or the rotation speed fall below the minimum rotation speed, the centrifugal switch returns to the normally open position, thereby breaking the circuit and cutting power to the heating element. 
     There is a long restart time for gas heating elements. In other words, after power has been cut from the heating elements, there is a long delay in returning the heating element to the same heat output as before the power was cut. For reversible dryers the long restart time presents a significant problem for dryers in which the drum shall change directions multiple times throughout a drying cycle. The restart time can add significant time to the drying cycle. For electric dryers the centrifugal switch typically carries higher current and reversible dryers would cause unnecessary activation and deactivation (i.e. “short cycling”) of the heating element. This would in return reduce the useful life (i.e. reliability) of the centrifugal switch. Simple removing or totally bypassing the centrifugal switch is not an option because removing or totally bypassing the centrifugal switch would remove an important safety feature that prevents runaway heating element conditions. That is, removing the centrifugal switch may lead to the heating element being energized when the drum is stationary for extended periods of time. 
     Having the above identified problems in mind, there exists a need for a dryer having a configuration that would allow the heating element to remain energized when the drum slows and reverses rotational direction while still preventing the heating elements from remaining energized while the drum is stationary for extended periods of time. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Consistent with embodiments of the present invention, dryer centrifugal switch bypass circuits for a dryer having a reverse tumbling action are disclosed. The dryer comprises a drum, a motor, a centrifugal switch, and a heating element. The centrifugal switch bypass circuit comprises a bypass relay operatively connected to the heating element and configured to bypass the centrifugal switch prior to the drum reversing rotational direction, and allow the heating element to remain energized during rotational direction reversal. The centrifugal switch bypass circuit further includes a relay hold circuit operatively connected to the bypass relay and configured to cause the bypass relay to continue bypassing the centrifugal switch during rotational direction reversal. 
     Still consistent with embodiments of the present invention, methods for bypassing a centrifugal switch are disclosed. The method may include receiving an indication that a drum is reversing rotational direction. The method may further include, once the drum begins reversing the rotational direction, utilizing a bypass relay to bypass the centrifugal switch. Finally, the method may include utilizing a relay hold circuit to cause the bypass relay to continue bypassing the centrifugal switch during reversal of the rotational direction. 
     Various aspects of the invention may include a relay hold circuit. The relay hold circuit may comprise an optocoupler configured to output a first signal and a NPN transistor configured to be activated by the first signal. The relay hold circuit may further include a field effect transistor configured to output a second signal to a first side of a bypass relay coil. Finally, the relay hold circuit may include a controller configured to determine when the bypass relay coil should be closed and provide a ground signal to a second side of the bypass relay coil to close the bypass relay coil when the controller determines that the bypass relay coil should be closed. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Non-limiting and non-exhaustive embodiments are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. 
         FIG. 1  depicts a control diagram for an electric dryer consistent with embodiments of the invention; 
         FIG. 2  depicts a control diagram for a gas dryer consistent with embodiments of the invention; 
         FIG. 3  depicts a wire diagram for a centrifugal switch bypass circuit consistent with embodiments of the invention; and 
         FIG. 4  depicts a simulation for the wiring diagram of  FIG. 3  consistent with embodiments of the invention. 
     
    
    
     GENERAL DESCRIPTION 
     Reference may be made throughout this specification to “one embodiment,” “an embodiment,” “embodiments,” “an aspect,” or “aspects” meaning that a particular described feature, structure, or characteristic may be included in at least one embodiment of the present invention. Thus, usage of such phrases may refer to more than just one embodiment or aspect. In addition, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments or aspects. Furthermore, reference to a single item may mean a single item or a plurality of items, just as reference to a plurality of items may mean a single item. Moreover, use of the term “and” when incorporated into a list is intended to imply that all the elements of the list, a single item of the list, or any combination of items in the list has been contemplated. Throughout this specification, electricity, power, and current may be used interchangeably. 
     Throughout this specification the centrifugal switch will be assumed to be a “normally open” switch and a rotating drum will be said to “throw” or “close” the centrifugal switch. However, it is contemplated that the centrifugal switch may be a “normally closed” switch and a rotating drum may be said to “open” the centrifugal switch. Whether a normally open or normally closed centrifugal switch is implemented, the desired result is that during drum rotation, the centrifugal switch allows the heating element to be activated. In addition, stating a drum is “not rotating” or any equivalent term implies that the drum is either stationary or rotating at a speed too slow to cause a centrifugal switch to be in the closed position. 
     During a drying cycle the drum may reverse rotational direction multiple times throughout the drying cycle. As a safety measure, centrifugal switches are utilized to deactivate a dryer&#39;s heating element when the drum is not rotating. Embodiments of the present invention utilize circuitry, as opposed to a purely software solution, for bypassing a centrifugal switch when reversing the rotational direction of the drum. The circuitry includes components that may create a time constant within the circuit that may limit the amount of time the bypass circuit may be allowed to bypass the centrifugal switch. Furthermore, the circuitry may monitor the rotation of the drum and override the time limit created by the time constant. Most importantly, the circuitry removes the dependence on software for providing the only failsafe to prevent the heating elements from activating when the drum fails to rotate or rotates slower than the required rotation speed. 
     DETAILED DESCRIPTION 
     Various embodiments are described more fully below with reference to the accompanying drawings, which form a part hereof, and which show specific embodiments of the invention. However, embodiments may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Accordingly, the following detailed description is, therefore, not to be taken in a limiting sense. 
     Referring now to the figures,  FIG. 1  depicts a control diagram for an electric dryer depicting a control side and a dryer side consistent with embodiments of the invention. Typically an electric dryer operates at 240 VAC with two hot wires (120 VAC each) as indicated by reference numerals  102  and  104  and one neutral wire, as indicated by reference numeral  106 , powering the dryer. Upon entering the dryer electricity flows through an outlet safety backup  108  and an inlet safety  110 . Outlet safety backup  108  and inlet safety  110  are thermostats used to cut power to the dryer should temperatures within the dryer exceed predetermined limits. After the electricity travels through outlet safety backup  108  and inlet safety  110 , it travels to a triac driver  112  and an inner coil relay  114 . After exiting inner coil relay  114 , electricity may flow to an inner heater coil  116  and after exiting triac driver  112 , electricity may flow to a heater triac  118  and to an outer heater coil  120 . 
     In order to achieve the required 240 VAC, electricity from hot wire  104  must travel through a centrifugal switch  122 . Centrifugal switch  122  may be a single pole double throw switch. In other aspects of the invention centrifugal switch  122  may be a single pole single throw switch. When the drum is not rotating centrifugal switch  122  is open and inner heating coil  116  and outer heating coil  120  do not receive the required 240 VAC needed for operation. Plus, neutral  106  is open preventing current from flowing between hot wire  102  and ground. Once the drum is rotating, centrifugal switch  122  is “thrown” thereby completing the circuit and allowing the dryer to operate as normal. 
     Hot wire  102  also provides power to an optocoupler  124 . Because optocoupler  124  is also connected to centrifugal switch  122 , optocoupler  124  does not receive power until the drum rotates and centrifugal switch  122  is thrown. During operation of the dryer optocoupler  124 , a bypass relay  126 , microcontroller  130 , and a relay hold up circuit  128  operate to keep inner heating coil  116  and outer heating coil  120  activated while the drum reverses its rotational direction. Note that bypass relay  126  may comprise any switching device. 
     To reverse the rotational direction of the drum, a controller may shut down the dryer motor. Once the drum has stopped, the polarity on the motor is reversed to cause the motor (i.e. the drum) to reverse rotation direction. During drum rotation, optocoupler  124  is used to power relay hold up circuit  128 , keeping capacitor  314  discharged. Before the drum begins to slow down in order to change rotational direction, bypass relay  126  bypasses centrifugal switch  122  thereby keeping inner heating coil  116  and outer heating coil  120  activated while the drum reverses its rotational direction. 
     Once the drum has returned to the desired rotation speed, bypass relay  126  opens and power flows through centrifugal switch  122 . If the drum does not reach the desired rotation speed, relay hold up circuit  128  may time out and cause bypass relay  126  to open and prevent or shut down inner heater coil  116  and outer heater coil  120 . The interactions of optocoupler  124 , bypass relay  126 , and relay hold up circuit  128  will be discussed further below with respect to  FIG. 3 . 
     Micropede  130  provides a ground path to a relay coil. Micropede  130  also monitors the state of the centrifugal switch (i.e. open or closed and controls drum rotation/direction and the heating elements via supplementary relays, triacs, etc. 
       FIG. 2  depicts a control diagram for a gas dryer depicting a control side and a dryer side consistent with embodiments of the invention. Typically a gas dryer operates at 120 VAC with one hot wire (120 VAC) as indicated by reference numerals  202  and one neutral wire, as indicated by reference numeral  206 , powering the dryer. Upon entering the dryer electricity flows through an igniter/shutoff valve relay  232 . Once igniter/shutoff valve relay  232  is powered, power flows through an outlet safety backup  208  and an inlet safety  210 . As described above, outlet safety backup  208  and inlet safety  210  are thermostats used to cut power to the dryer should temperatures within the dryer exceed predetermined limits. After the electricity travels through outlet safety backup  208  and inlet safety  210 , it travels to an igniter/shutoff valve module  234 . Note that igniter/shutoff valve module  234  may be a two-stage gas valve. 
     In order to complete the circuit and allow igniter/shutoff valve module  234  to activate, electricity from neutral wire  206  must travel through a centrifugal switch  222 . Centrifugal switch  222  may be a single pole double throw switch. In other aspects of the invention centrifugal switch  122  may be a single pole single throw switch. When the drum is not rotating centrifugal switch  222  is open and igniter/shutoff valve module  234  does not activate because the circuit is broken. Once the drum is rotating, centrifugal switch  222  is “thrown” thereby completing the circuit and allowing the dryer to operate as normal. 
     Hot wire  202  also provides power to an optocoupler  224 . Because optocoupler  224  is also connected to a centrifugal switch  222 , optocoupler  224  does not receive power until the drum rotates and centrifugal switch  222  is thrown. During operation of the dryer optocoupler  224 , a bypass relay  226 , microcontroller  130 , and a relay hold up circuit  228  operate to keep igniter/shutoff valve module  234  activated while the drum reverses its rotational direction. 
     To reverse the rotational direction of the drum, a controller may shut down the dryer motor. Once the drum has stopped, the polarity on the motor is reversed to cause the motor (i.e. the drum) to reverse rotation direction. During drum rotation, optocoupler  224  is used to power relay hold up circuit  228  keeping capacitor  314  discharged. Before the drum begins to slow down in order to change rotational direction, bypass relay  226  bypasses centrifugal switch  222  thereby keeping igniter/shutoff valve module  234  activated while the drum reverses its rotational direction. The interactions of optocoupler  224 , bypass relay  226 , and relay hold up circuit  228  will be discussed further below with respect to  FIG. 3 . 
     Referring now to  FIG. 3 ,  FIG. 3  will be described with respect to an electric dryer as described in  FIG. 1 .  FIG. 3  depicts a wire diagram for a centrifugal switch bypass circuit  300  consistent with embodiments of the invention. Centrifugal switch bypass circuit  300  provides a time period in which bypass relay  126  may bypass centrifugal switch  122  to allow the drum to reverse its rotational direction. For discussion purposes, the time period with which  FIG. 3  will be described is six seconds. However, it should be understood that the time period may be longer or shorter than six seconds. In addition, the time period need not be fixed. As will be discussed below, the time period may be controlled by a controller  340 . 
     Centrifugal switch bypass circuit  300  receives 120 VAC from hot wire  104 . During drum rotation, centrifugal switch  122  closes and electricity flows through resistors. While three resistors are shown in  FIG. 3 , in other aspects of the invention a single resistor or multiple resistors of various resistance may be used to achieve a desired resistance. A diode controls the current flow. 
     After flowing through the resistors, current flows to optocoupler  124  which isolates the 120 VAC circuit from the DC low voltage circuits. When centrifugal switch  122  is closed, optocoupler  124  allows a signal  316  (e.g. 5 VDC), which acts as feed back to controller  340 , to indicate that centrifugal switch  122  is closed. In addition, when centrifugal switch  122  is closed, optocoupler  124  allows signal  316  to reach a NPN transistor  310 . Signal  316  activates NPN transistor  310  which allows bypass relay  126  to be activated, thereby bypassing centrifugal switch  122 . When the NPN transistor is on, capacitor  314  is discharged, thereby allowing a field effect transistor (MOSFET) to be in the “on” state and power one side of the by-pass relay. 
     When centrifugal switch  122  is open, signal  316  is not allowed to activate NPN transistor  310 . When NPN transistor  310  is not active a capacitor  314  begins to charge with a signal  318  (e.g. 12 VDC). Once the charge on capacitor  314  reaches a predetermined level, MOSFET  312  is deactivated by signal  318 . In general, once capacitor  314  is charged it deactivates MOSFET  312  which in turn disables bypass relay  126  so that controller  340  cannot control bypass relay  126 . 
     When centrifugal switch  122  is closed, controller  340  has the ability to control bypass relay  126  via a backside connection to bypass relay  126  as indicated by reference numeral  330 . For instance, when the drum is about to reverse its rotational direction, controller  340  closes bypass relay  126  so that inner heating coil  116  and outer heating coil  120  may continue to receive power while the drum reverses and centrifugal switch  122  is open. When centrifugal switch  122  opens capacitor  314  begins charging and once it charges, it deactivates MOSFET  312 . If the drum has not begun to rotate by the time MOSFET  312  is deactivated, centrifugal switch  122  is open and bypass relay  126  opens thereby cutting power to inner heating coil  116  and outer heating coil  120 . 
     In the current example capacitor  314  is a 100 μF capacitor and time delay generated by the RC circuit is six seconds. The time delay may be adjusted by replacing the resistor in the RC circuit with a rheostat and having controller  340  adjusting the rheostat resistance. 
     Turning now to  FIG. 4 ,  FIG. 4  depicts a simulation for the wiring diagram of  FIG. 3  consistent with embodiments of the invention. From 0-1 second centrifugal switch  122  is closed and signal  316  is being allowed to reach NPN transistor  310 . At 1 second, centrifugal switch  122  opens and capacitor  314  begins charging as indicated by reference numeral  406 . After approximately 6 seconds capacitor  314  reaches a predetermined voltage and MOSFET  312  deactivates. When MOSFET  312  deactivates, signal  318  stops and bypass relay  126  opens. At approximately 10 seconds, centrifugal switch  122  closes and capacitor  314  discharges as indicated by reference numeral  406 . Once capacitor  314  drops below a predetermined voltage and MOSFET  312  activates. When MOSFET  312  activates, signal  318  supplies voltage to one side of the bypass relay  126 . The bypass relay  126  is allowed to be activated via the micropede  340 . 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.