Temperature limiting arrangement for a glass-ceramic cooktop appliance

In a household cooking appliance of the type having a ceramic glass-ceramic cooking surface for supporting loads to be heated, and at least one radiant heating unit disposed beneath the glass-ceramic cooking surface to heat loads supported thereon, a power control system comprising:

• user actuable input selection means for enabling the user to select one of a plurality of power settings for the heating unit;
• temperature sensing means for sensing the temperature of the glass-ceramic support surface proximate the heating unit., and
• power control means responsive to said input selection means and said temperature sensing means, and operative to operate the heating unit at a steady state power level corresponding to the user selected power setting;
• said power control means including means for comparing the sensed glass-ceramic temperature to a first predetermined reference temperature, means for measuring the rate of change of the sensed glass-ceramic temperature;
• means for comparing the rate of change of the sensed glass-ceramic temperature to a positive reference rate of change representative of an abnormal load condition on the glass-ceramic cooking surface, means for comparing the measured glass-ceramic temperature to a second reference temperature higher than said first reference temperature, representative of an undesirably high glass-ceramic temperature and means for comparing the measured rate of change to a negative reference rate of change when the sensed temperature exceeds said second reference value;
• said power control means being operative to operate the heating unit at a power level lower than the steady state power level associated with the user selected power setting when said sensed temperature is greater than said first reference temperature and said positive reference rate of change, or when said sensed temperature is greater than said second reference temperature and the measured rate is less negative than the negative reference rate of change, the lower power level being determined as a function of the sensed glass-ceramic temperature, the measured rate of change and the user selected power setting;
• whereby as the glass-ceramic is heating up, the power is lowered when the temperature rate of change indicates the existence of an abnormal load condition characterized by an undesirably rapid increase in temperature, and the power level applied to the heating unit is also lowered if the temperature of the glass-ceramic is at an undesirably high temperature and is not decreasing at a satisfactory rate.

An electronic controller for a household cooking appliance of the type having a glass-ceramic cooking surface for supporting loads to be heated, and at least one radiant heating unit disposed beneath the glass-ceramic cooking surface to heat loads supported thereon, user actuable input selection means for enabling the user to select one of a plurality of power settings for the heating unit, and temperature sensing means for sensing the temperature of the glass-ceramic support surface proximate the heating unit, said electronic controller comprising:

• power control means responsive to the input selection means and the temperature sensing means, operative to apply a steady state power level corresponding to the user selected power setting to the heating unit;
• means for determining the rate of change of the sensed glass-ceramic temperature;
• and
• means for monitoring the glass-ceramic temperature and the temperature rate of change to detect an abnormal thermal load condition on the glass-ceramic cooking surface;
• said power control means being further operative in response to detection of an abnormal load condition to operate the heating unit at a power level lower than the steady state power level associated with the user selected power setting, said lower level being determined as a function of the sensed glass-ceramic temperature, the temperature rate of change, and the user selected power setting, to limit the temperature of glass-ceramic cooking surface so as to avoid damage by excessive temperatures resulting from abnormal thermal load conditions on the cooking surface.

A method of controlling power in a cooking appliance of the type having a radiant heating unit disposed beneath a glass-ceramic cooking surface with means for sensing the temperature of the glass-ceramic cooking surface proximate the heating unit, user actuable input selection means for enabling the user to select from a plurality of power settings for the heating unit, said power control method comprising the steps of:

• operating the electric heating unit at a steady state power level corresponding to the user selected power setting;
• periodically measuring the glass-ceramic cooking surface temperature and comparing the measured temperature to a threshold reference temperature;
• when the measured temperature is above the threshold temperature, periodically computing the rate of change of the measured temperature and comparing the computed rate to a reference rate representing an abnormal load condition on the cooking surface., and
• when the measured rate is greater than the reference rate, reducing the power level applied to the heating unit as a function of the measured glass-ceramic temperature, the measured rate of change of the glass-ceramic temperature, and the user selected power setting to protect the glass-ceramic cooking surface from excessive temperatures.