Heating Plate with Cooking Oil Ignition Prevention for Electric Cooking Apparatus

Abstract

An electric heating plate for electric cooking apparatuses is provided with the capability to prevent unintended ignition of cooking oil. The heating plate includes an electric heating conductor as the heat source and a temperature controller electrically connected with the heating conductor, sensing the temperature of the cooking vessel, controlling the heating plate output power, and limiting the temperature of the cooking oil in the cooking vessel. With this heating plate, the electric cooking apparatus will be able to prevent cooking oil ignition during cooking, while the minimum cooking temperature for a daily cooking is still maintained.

Claims

1. A heating plate for electric cooking apparatuses, comprising: an electric heating conductor; a temperature controller installed on the heating plate and electrically connected with the heating conductor; the temperature controller, comprising: a temperature transfer device (the device), touching the cooking vessel for transferring temperature of the cooking vessel to the control unit, and a control unit for adjusting the output power of the heating plate; the control unit compares the transferred temperature with predetermined upper and lower temperature limits derived from an established relationship between the transferred temperature and the cooking oil temperature during cooking, whereby, under the rated power of the heating plate, when the transferred temperature reaches the upper temperature limit, the control unit reduces output power of the heating plate, and when the transferred temperature reaches the lower temperature limit, the control unit increases output power of the heating plate, such that the cooking oil temperature within the cooking vessel is limited in a controlled cycle and kept below the cooking oil ignition point while still maintains the minimum temperature for daily cooking.

2. The heating plate according to claim 1, wherein the upper temperature limit is determined based on the cooking oil ignition point and the established relationship between the transferred temperature to the control unit by the device and the cooking oil temperature within the cooking vessel, which takes into account the device design and placement, the control unit type, the heating plate output power, the cooking vessel type, whereby the upper temperature limit is reached when the maximum cooking oil temperature in the cooking vessel approaches but never reaches the cooking oil ignition point.

3. The heating plate according to claim 1, wherein the lower temperature limit is determined based on the minimum temperature required for daily cooking and the established relationship between the transferred temperature and the cooking oil temperature within the cooking vessel, whereby the lower temperature limit is reached when the cooking oil temperature in the cooking vessel reaches the minimum temperature required for daily cooking.

4. The heating plate according to claim 1, wherein the lower end of the device is mounted on the sensing part of the control unit, which is placed in a cold area away from the heating conductor and the cooking vessel; the top end of the device is raised higher than the heating plate by an elastic mechanism, making a solid, direct contact between the device's top end and the cooking vessel; whereby during cooking, the device's top end heated by the cooking vessel, the device's lower end in the cold area, and the other part of the device insulated by the heat insolation layer form a heat pipe effect ensuring a highly efficient temperature transfer from the cooking vessel to the control unit.

5. The heating plate according to claim 1, wherein a multi-layer heat insulation/reflection is placed between the heating conductor and the control unit to reduce the air temperature around the control unit, and to improve the energy efficiency of the heating plate.

6. The heating plate according to claim 1, wherein the heating plate is raised to increase airflow under the plate to reduce the air temperature around the control unit.

7. The heating plate according to claim 1, wherein the heating plate has a rated output power between 750 W and 3500 W.

8. The heating plate according to claim 1, wherein the control unit of the temperature controller is an ON/OFF switch.

9. The heating plate according to claim 1, wherein the control unit of the temperature controller is a set of relays which controls the output power of the heating plate by multi step adjustment.

10. The heating plate according to claim 1, wherein the control unit of the temperature controller is configured to adjust the input voltage of the heating plate by using a silicon-controlled rectifier (SCR) to achieve output power adjustments.

11. A method of applying temperature limiting control on the cooking vessel on an electric heating plate to prevent cooking oil ignition while maintain a desired cooking performance; the method comprises a. testing to establish the temperature transfer relationship among the heating plate surface, the cooking vessel, the cooking oil in the vessel, and the temperature controller during cooking; b. based on said relationship, setting up an upper temperature limit for the temperature controller to limit the maximum cooking oil temperature below the oil ignition point, and setting up a lower temperature limit for the temperature controller to maintain the minimum cooking oil temperature required for daily cooking; c. creating a cold area away from the heating source to place the control unit of the temperature controller; designing a temperature transfer device to transfer the cooking vessel temperature to the control unit; d. comparing the transferred temperature with upper/lower temperature limits; reducing output power of the heating source when the transferred temperature reaches the upper temperature limit; or increasing output power of the heating source when the transferred temperature reaches the lower temperature limit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a cross-sectional view of one embodiment of the heating plate

[0013] FIG. 2 is a top perspective view the of the heating plate shown in FIG. 1

[0014] FIG. 3 is a top perspective view showing another embodiment of the heating plate

[0015] FIG. 4 is a cross-sectional view of the heating plate shown in FIG. 3

[0016] FIG. 5 is a top perspective view of an alternate embodiment of the heating plate

[0017] FIG. 6 is a cross-sectional view of the heating plate shown in FIG. 5

DETAILED DESCRIPTION

[0018] In one embodiment, as shown in FIG. 1 FIG. 2, the heating plate includes heating wire 1, which is in a metallic tube 11 and insulated by Magnesium Oxide powder 12, and a temperature controller composing a temperature transfer device 3 and a control unit 8 connected in series with the coil heating wire 1. The device is made of high thermal-conductivity metal, surrounded by the heat insulation layer 4, and covered by a metal cap 2. The device's lower end is mounted on the temperature sensing part of the control unit, while the control unit is mounted on an elastic mechanism 9, a metal spring leaf, under the plate, away from the heat source, the heating wire and the cooking vessel. Therefore, the control unit and the lower end of the device are in a cold area, in which the temperature is at least 70 C./158 F. lower than the cooking vessel bottom. The temperature controller and the device are raised by the metal spring leaf, wherein the top end of the device is higher than the plate surface. When a cooking vessel is placed on the heating plate, the cooking vessel bottom presses against the top end of the device, making a solid, direct contact between the device's top end and the bottom of the cooking vessel. During cooking, the device's top end heated by the cooking vessel bottom, the device's lower end in a cold area, and the other part of the device insulated by the heat insolation layer form a heat pipe effect, which ensures a highly efficient temperature transfer from the cooking vessel to the control unit.

[0019] A multi-layer heat insulation/reflection pad 6/7 is set between the control unit and the heating wire to reduce the air temperature around the control unit and the device's lower end, making the cold area cooler. The pad reflects the heat from the heating wire to the plate surface. This increases the power efficiency of the heating plate.

[0020] The table below shows an example of this embodiment, wherein the temperature controller includes the device, a 45 mm long, 16 mm diameter rod made of Aluminum6061, and a control unit, Z3-250-200 thermostat made by DongLing. The controller is raised by a stainless-steel spring leaf, 40 mm8 mm0.2 mm, with two ends mounted on the bracket 10. The top end the device is 5 mm higher than the heating plate surface, and the control unit is 35 mm lower than the plate surface. The heating plate is 8 with a power rating of 2400 W. The heat insulation/reflection pad is a 1 mm thick, 150 mm Aluminum disc 6 and 5 mm thick fiberglass insulation layer 7.

TABLE-US-00001 Predetermined temperature Temperature Temperature of Temperature limits in the cooking the cooking vessel transferred to the for control unit oil ( C.) bottom ( C.) control unit ( C.) ( C.) 200 220 140 250 275 200 200, Lower temperature limit 285 305 225 320 340 250 250, Upper temperature limit

[0021] For a cooking under the rated power of the heating plate, when the temperature of the cooking oil approaches 320 C., whereby the temperature transferred to the control unit reaches the upper temperature limit, 250 C., the control unit turns off the power of the heating wire and causes the heating wire to stop generating heat; when the temperature of the cooking oil drops to 250 C., the temperature transferred to the control unit reaches to the lower temperature limit, 200 C., the control unit turns on the power of the heating wire causing the heating wire to generate heat. A controlled temperature cycle for the cooking oil in the cooking vessel is formed; the temperature of the cooking oil is limited below 320 C., which is below the cooking oil ignition point, and the minimum cooking oil temperature is kept above 250 C., the cooking oil boiling point, to maintain a desired cooking performance.

[0022] In another embodiment, as shown in FIG. 3 and FIG. 4. whereby, a temperature controller composing the device 3 made of high thermal-conductivity metal, surrounded by the heat insulation layer 4, and covered by a metal cap 2. The device forms a L shape cantilever working as an elastic mechanism to push the top end of the device higher than the plate surface. The device's lower end is mounted on the temperature sensing part of the control unit 8, which is placed under the heating plate and away from the heating source, the heating wire and the cooking vessel. Therefore, the control unit and the lower end of the device are in a cold area. When a cooking vessel is placed on the heating plate, the cooking vessel presses against the top end of the device, making a solid, direct contact between the device's top end and the bottom of the cooking vessel. During cooking, the device's top end heated by the cooking vessel bottom, the device's lower end in a cold area, and the other part of the device insulated by the heat insolation layer form a heat pipe effect, which ensures a highly efficient temperature transfer from the cooking vessel to the control unit.

[0023] The table below shows an example for this embodiment, where the device is 60 mm long (45 mm vertical+15 mm horizontal), 6 mm diameter L shape cantilever made of Aluminum5052, and covered by 5 mm thick fiberglass insulation. The control unit is a thermostat, DongLing Z3-225-210, and placed 35 mm lower than the plate surface. The heating plate is 8 with a power rating of 2400 W.

TABLE-US-00002 Predetermined temperature Temperature Temperature of Temperature limits for in the cooking the cooking vessel transferred to the control unit oil ( C.) bottom ( C.) control unit ( C.) ( C.) 200 220 180 250 265 210 210, Lower temperature limit 285 310 190 320 340 225 225, Upper temperature limit

[0024] For a cooking under the rated power of the heating plate, the upper and lower limits of the control unit are accordingly set to control the bottom temperature of cooking vessel to maintain a desired cooking performance while not exceeding the cooking oil ignition temperature.

[0025] In an alternate embodiment, as shown in FIG. 5 and FIG. 6, the temperature controller including a control unit 8 and a disc temperature transfer device 3. The lower end of device is mounted on the control unit, while the control unit is mounted on an elastic device 9 lifting the temperature controller above the heating plate surface. When the cooking vessel is placed on the heating plate, the temperature controller is depressed by the bottom of the cooking vessel to the same level as the heating plate. This makes a solid, direct contact between the temperature transfer device and the bottom of the cooking vessel, and ensures a real-time temperature transfer from the cooking vessel bottom to the control unit.

[0026] The table below shows an example of this embodiment, wherein the device is 5 mm long, 20 mm diameter rod made of Aluminum 5052, and lifted 5 mm higher than the heating plate. The control unit, a bi-metal thermostat Y23-16-315-245 made by DongLing, is mounted on a high temperature stainless steel spring, YPmetel NGW002-10-0.15. The plate is 8 with a power rating of 2400 W.

TABLE-US-00003 Predetermined temperature Temperature Temperature of Temperature limits for in the cooking the cooking vessel transferred to the control unit oil ( C.) bottom ( C.) control unit ( C.) ( C.) 200 220 185 250 260 245 245, Lower temperature limit 300 315 280 320 340 315 315, Upper temperature limit

[0027] For a cooking under the rated power of the heating plate, the upper and lower limits of the control unit are accordingly set to control the bottom temperature of cooking vessel to maintain a desired cooking performance while not exceeding the cooking oil ignition temperature.

[0028] In some embodiments, the heating plate is raised by 520 mm to achieve better airflow under the plate to further reduce the air temperature around the control unit and the low end of the device. In some embodiments, the heating plate may have a rated output power between 750 W and 3500 W.

[0029] In some embodiments, the electric heating conductor may be made of metal, nonmetallic heat conduction material, or mixed metal and nonmetallic material.

[0030] In some embodiments, the control unit of the temperature controller may be a thermostat based ON/OFF switch.

[0031] In some embodiments, the control unit of the temperature controller may also be a set of relays which controls the output power of the heating plate by multi step adjustment.

[0032] In some embodiments, the control unit of the temperature controller can adjust the input voltage of the heating plate by using a silicon-controlled rectifier (SCR) to achieve power adjustments.

[0033] A number of preferred embodiments have been fully described above with reference to the drawing figures. The scope of the claims should not be limited by the preferred embodiments and examples but should be given the broadest interpretation consistent with the description as a whole.