Patent Publication Number: US-2013247778-A1

Title: Enhanced safety for electrical appliances such as toasters

Description:
This application claims benefit of U.S. provisional application Ser. No. 61/615,215, filed Mar. 24, 2012. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a circuit arrangement which provides enhanced safety for electrical appliances such as toasters. 
     BACKGROUND OF THE INVENTION 
     Protective circuit arrangements have been provided in the past to protect electrical devices such as electrical appliances and personnel or users of the devices when undesirable conditions develop within the device. Examples of such arrangements are set forth in the applicant&#39;s prior U.S. Pat. No. 6,525,914—Protection System for Devices Connected to an Alternating Current Electrical Power Supply, and U.S. Pat. No. 6,829,123—Device Safety System and Method. While the systems set forth in these patents various levels and types of protection for electrical devices, they are because of the number and type of electrical components involved and assemble costs, quite expensive when considered as a part of the overall cost of the device in which they are provided for protection. 
     Manufacturers of electrical appliances are continually trying to reduce the cost of manufacturing the appliances. As the cost of manufacturing the appliance decreases, the relative cost of protective circuit arrangements such as those set forth in the above mentioned patents becomes much greater, such that the manufacture becomes more reluctant to include them in the appliance. Rather than not include protective arrangements in an appliance, it is desirable to provide protection in a relatively less costly way. 
     While electrical appliances are designed to be reliable and safe to use, unsafe conditions can develop such as due to a failure in a component of the appliance, or due to miss-use of the appliance. For instance, an electrical toaster may present the following unsafe conditions. The elevator carriage may become jammed in the down position, thereby keeping the electrical heating elements activated. Excessive leakage currents from metal parts to electrically live parts such as the elements, may develop, such as caused by a build up of crumbs and grease between the metal parts and electrically live parts. Fire or flames developing within the toaster. A contact being made between the metal frame and electrically live parts by person sticking a metal object, such as a knife into the toaster. It is therefore desirability to include automatic protective features in certain consumer appliances that will contribute to both the protection of property and consumer safety. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of this invention to provide enhanced safety to consumer appliances, such as a toaster at a cost that will allow the general market product sales price be at a level the average consumer can afford. It is a further object of this invention to provide the maximum amount of safety at the lowest possible cost. 
     In accordance with this invention enhanced safety features are provided to toasters and other electrical appliances. Power is removed from the appliance, when a fire (flame) occurs within the appliance. Removing the power source is essential to limit the time duration in the event of such an occurrence. Further, for elevator type toasters it is important to maintain the elevator carriage in the down position to avoid the spreading of flaming debris outside of the toaster when the elevator carriage pops up. Further, electrical power is removed from the accessible live parts of the appliance when excessive electrical leakage currents occur, or an electrically conductive contact is established between the metal frame and live parts. Further, an audible or visual alarm may be provided in the event of any of the above mentioned situations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a prior art schematic circuit diagram for a pop-up toaster; 
         FIG. 2  is a prior art schematic circuit diagram for a pop-up toaster provided with an alternative power disconnect relay 
         FIG. 3  is a circuit block diagram of the enhanced safety system for an electrical appliance in accordance with this invention; and 
         FIG. 4  is a detailed schematic circuit diagram for a pop-up toaster in accordance with a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In setting forth the detailed description of the drawings, the same numerals will be used for corresponding elements in the figures. 
     Referring to  FIG. 1 , a basic prior art toaster electrical circuit is shown. The circuit includes a plug  2  for connecting to an AC power source. Electrical heating elements  4  of the toaster are connected to the power source when the contacts  6  of a power switch  8  are closed. To initiate use of the toaster, the contacts  6  are closed, thereby energizing the heating elements  4  and a timer control  10 . The opening of the contacts  6 , by the power switch  8  is initiated by the release of the toaster elevator carriage by the timer control  10 . The contacts  6  or the power switch  8  are mechanically or electrically locked in the closed position until the release of the toaster elevator carriage provides an input to the switch  8  to open the contacts  6 . 
     Referring to  FIG. 2 , again a basic diagram of a typical “pop up” toaster is shown. The toast elevator carriage may be held down mechanically by a solenoid, or electrically by use of an electromagnet. Again, the carriage pop up release is controlled by the timer control  10 . Contacts  12  of alternative power disconnect relay  14  are closed during normal operation of the appliance and open in response to a fault condition thereby removing power to the heater elements. 
     The addition of the alternative power disconnect relay  14  is necessary to ensure that the heater element power source will be removed under fault conditions in particular when the elevator carriage is maintained in the latched position, such as when a fire is initiated in the toaster compartment. Popping up of the elevator carriage could result in the distribution of flaming debris outside of the toaster. An example of another adverse condition would be that of a jammed down elevator carriage. Without the opening of the contacts over-heating and ignition of a fire in the toaster or of surrounding material would result. Upon detecting an adverse condition, an input signal is provided to the alternative power disconnect relay  14 , to open the contacts  12 , thereby removing power from the heating element  4 . While the heating element  4  is de-activated, the power switch  8  remains activated, thereby preventing the release of the carriage, and the adverse consequences that could result from the release. 
     Referring to  FIG. 3 , a block diagram of an electrical appliance provided with the added protection in accordance with a preferred embodiment of this invention. The appliance being protected  11 , includes connections  13  to a power supply, the appliance electrical load  15 , and circuit interrupter contacts  17 . The enhanced safety system of this invention shown as  19 , includes a circuit power supply  21 , which is activated from a power supply through connection  13 . A circuit interrupter and alarm  23  includes a coil  25  for actuating the contact of a circuit breaker to remove power from the appropriate components of the appliance to terminate incipient or action dangerous conditions. An alarm  27  is also activated along with the coil  25 . The energization of the coil  25  and alarm  27  is provided by a fault activation switch device  29 . The power supplied to the coil  25  and the alarm  27  by the fault switch device  29 , may vary in magnitude, such that the alarm  27  will be activated at a lower power level than the coil  25 , to given advanced warning of a dangerous condition. As shown in  FIG. 3 , the fault activation switch device  29 , may receive fault signals to activate the coil  25  and the alarm  27 , from a variety of sensors. Sensors shown are a flame sensor  31 , a leakage current sensor  33 , and other sensor  35 . In an alternative circuit arrangement, the coil of alternative power disconnect relay  14  may be normally activated and the coil de-activated with detection of a fault. 
     The flame sensor  31  includes a light responsive element which is positioned in the appliance to detect light indicative of an incipient or actual fault condition. Reflectors, refractors, or other devices may be included in the appliance to direct the light indicative of an incipient or actual fault condition to the light responsive element. 
     The leakage current sensor  33 , configured to sense a leakage current between the live circuit components within the appliance an the metal housing. This leakage current may be due to electrical insulation failure, or the insertion of a metal object in the appliance which establishes a conductive path between live circuit elements and the metal housing. The detection and alarm indication of excessive electrical leakage currents within the appliance could well prevent a serious hazardous event from occurring, and may provide early warning of pending fault conditions such as, insulation failure, carbonized path, and tracking that can lead to dangerous electrical arcing. Further, the build up of grease, crumbs or other electrically conductive substances would provide the consumer user a reason to clean the appliance. 
     The other sensor  35 , is intended to indicate that sensors which could detect other types of incipient or actual dangerous conditions in the appliance may be provided. 
     Referring to  FIG. 4 , a typical basic toaster circuit is shown with details of the added protection and visual display circuit in accordance with a preferred embodiment of this invention. This added protection is provided in the event of: Excessive leakage currents or contact between metal frame and live parts, compartment flame (fire), and a jammed elevator carriage. As in the typical pop up toaster, power is provided to the toaster elements  4  through the closed contacts  6  when the spring loaded elevator carriage is held in the down position by the action of either a mechanical latch or an activated electromagnet. The timer controller  10  will release the elevator carriage to it&#39;s up position when the time period for the toaster setting has been achieved, and will remove power from a solenoid  8 , to open contacts I, removing power from all circuits within the toaster. 
     Referring to the specific circuitry of the preferring embodiment of this invention, a DC power supply includes a diode  16  a capacitor  18 , and a voltage regulator formed by resistor  20  and zener diode  22 , which are standard and well known circuits. 
     In the event of jamming of the elevator carriage in the down position the heating elements  4  may continue to be activated and a fire could result. Should this situation occur, the timer control  10  can be suitably connected to provide a signal to the gate of SCR  26  thus energizing the coil of the alternative power disconnect relay  14  and remove power from the heating elements  4  by opening contacts  12 . 
     If a flame or fire occurs within the toaster compartments a light sensitive resistor or similar light sensitive component  24  positioned within the toaster will detect the scattered or emitted light that is created and gate SCR  26  through a time delay circuit which includes resistor  28 , capacitor  30 , diode  16 , capacitor  18 , zener diode  22 , and resistor  32 , into a conductive state energizing the coil of alternate power disconnect relay  14  and removing the power source from the heating elements  4  by opening contacts  12 . It is important to maintain the elevator carriage in the down position to prevent the spreading of flaming debris. This is accomplished is the case of a mechanically latched solenoid  8  arrangement by removing the power source to solenoid  8  or the timer control  10  when the coil of alternate power disconnect relay  14  is activated. Alternatively, in the case of a solenoid  8  electro magnet arrangement power may be maintained to the coil  8  through a diode  36 , a diode  38  and a resistor  40 . 
     It is also desirable to remove power from the toast if any contact is made between the metal casing of the toaster and electrically live parts. For example, a user of the toaster might try to dislodge a slice of bread with an electrically conductive implement. Removal of the power is accomplished by detecting low level electrical current flow between the metal casing of the toaster and an electrically live part. A contact between the metal casing  44  and an electrically live part is detected by the circuit consisting of resistor  44  and diode  46 . The detection of a low level electrical current through resistor  44  and diode  46  is applied as a forward bias to transistor  42 , thereby providing a gating signal to SCR  26  and energizing the solenoid of alternate power disconnect relay  14 , opening contacts  12  to de-energize the heating elements  4 . 
     To further describe the circuit of the preferred embodiment of this invention, capacitor  47  and resistor  48  provide noise and detection level control. A series circuit of a light emitting diode  50  and a resistor  52  is connected in parallel with alternate power disconnect relay  14 , thereby providing a visual fault display. An audible fault indication could be provided by using a piezo or similar type alarm connected in place of, or in parallel with the light emitting diode  50  and resistor  52 . 
     While a preferred embodiment of the circuit arrangement of this invention which provides enhanced safety for electrical appliances such as toasters has been shown, it should be apparent to those skilled in the art that what has been shown and described is considered at present to be a preferred embodiment of the circuit arrangement and system of this invention. While a preferred embodiment of the circuit arrangement of this invention has been shown and described other circuit arrangements are contemplated by this invention. In accordance with the Patent Statutes, changes may be made in the enhance safety arrangement for electrical appliances of this invention without actually departing from the true spirit and scope of this invention. The appended claims are intended to cover all such changes and modifications which fail in the true spirit and scope of this invention.