Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
1999-12-15
2001-05-15
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S413000, C219S393000, C219S396000, C219S391000
Reexamination Certificate
active
06232584
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to cooking ovens, and more particularly to a self-cleaning system for an oven which is capable of automatically eliminating food soils accumulated on its walls by a pyrolytic process at a high temperature.
2. Description of the Related Art
It is well known, as disclosed in U.S. Pat. Nos. 3,962,561 and 4,481,404, that cooking ovens such as electric ovens, gas ovens and convection microwave ovens can not only be used for normal cooking but also can pyrolytically eliminate food soils attached to its walls during the normal cooking. The pyrolytic elimination can be effected by heating and maintaining the cooking chamber at a high cleaning temperature—such as between 800° F. -850° F. —for one to four hours. As soils are pyrolytically degraded, exhaust products are produced such as water vapor, carbon monoxide, carbon dioxide and others including partially combusted or degraded soil particles which produce smoke and odors. It is known that a catalyst, located in the exhaust duct of an oven, can be used to further degrade or oxidize the partially combusted products, thereby minimizing smoke and odors that are exhausted into the ambient atmosphere—typically a kitchen.
The typical self clean cycle is effected by having a user select a self clean option. Initiation of the self clean cycle will set a high control temperature for the oven, cause the oven door to be locked immediately or at some predetermined time or temperature and proceed to heat the oven cavity to a relatively high temperature for a predetermined time before ending the heating cycle, allowing cooling to occur and then releasing the door lock as an end to the self clean cycle.
The cleaning time actually needed to pyrolytically clean a cooking chamber greatly depends on the amount of food soils in the cooking chamber. In the case of light food soils, the soil-elimination is sufficiently effected with a relatively short cleaning period, such as a cleaning time of about one hour (about ½ hour for heating-up and about ½ hour for cooling-off). On the other hand, in the case of heavy food soils, the chamber temperature must be maintained at the cleaning temperature for about three hours. As a result, the cleaning time is about four hours for a worst case/heavy food soil condition (about ½ hours for heating-up, about three hours for keeping the cleaning temperature and about ½ hours for cooling-off).
In order to ensure that the self clean cycle adequately cleans the oven chamber, the self clean time period is commonly determined by assuming a worst case cycle. Accordingly, the predetermined self cleaning cycle time is generally set at about 4 hours. Setting the self clean cycle under a worst case analysis wastefully consumes energy and unnecessarily requires long cleaning periods.
To address this problem of wasteful energy use during self clean, there have been some past attempts to monitor the progress of a self clean cycle and to control the duration of a self clean cycle to only the time actually needed to degrade and remove soils from the oven chamber. For example, U.S. Pat. No. 4,954,694, discloses a system wherein a gas sensor monitors the exhaust gases produced during a self clean cycle and determines the self clean heating time in response to the exhaust gas component variation.
SUMMARY OF THE INVENTION
The present invention is directed to an oven system which is capable of monitoring the progress of a self clean operation and controlling the duration of the self clean operation in response to sensed conditions. In particular, the present invention takes advantage of the operation of a catalyst positioned within an oven exhaust passage for oxidizing smoke and odors which result from the self clean operation. It has been observed that heat is generated as a result of the exothermic chemical reactions which occur on the catalyst surface as the catalyst stimulates the oxidation of partially combusted soil products pyrolytically cleaned from the oven cavity. As the exothermic chemical reaction occurs on the catalyst, the surface temperature of the catalyst and the temperature of the exhaust gases after they pass through the catalyst are greater than the temperature of the exhaust gases before they enter the catalyst area. The amount of heat generated by the catalyst and its corresponding increase in temperature is related to the amount of material being combusted within the oven cavity. If combustion of soils within the cavity is occurring, heat is generated on the catalyst whereas, upon completion of soil combustion, heat is no longer generated on the catalyst. It should be noted that upon completion of soil combustion, cleaning may still be occurring but since combustion is complete, there is nothing left to react on the catalyst.
Accordingly, a method and apparatus is provided for operating a self cleaning oven wherein the monitoring of exothermic chemical reactions within a catalyst can be used to determine when the combustion of food material is complete, in order to terminate a self cleaning cycle.
More particularly, the present invention is directed to a self cleaning oven having an oven cavity or cooking chamber and a heating device for supplying heat into the oven cavity. An exhaust passage extends from the cooking chamber and leads to the ambient atmosphere. A catalyst is disposed in the exhaust passage. A first temperature sensor senses the catalyst inlet temperature and a second temperature sensor senses the catalyst surface or outlet temperature. A controller controls the oven in accord with a method of operation that includes accepting an input to begin a self cleaning operation. The heating device is then controlled to heat and maintain the oven cavity at an oven clean temperature suitable for oven cleaning. The catalyst inlet temperature (T
i
) and the catalyst surface or outlet temperature (T
o
) are sensed. The self clean cycle is terminated a predetermined time after the catalyst outlet temperature (T
o
) has exceeded and then fallen below the catalyst inlet temperature (T
i
).
The present invention may include initially setting a timer to control the length of the self clean cycle equal to a full cycle value (t
fc
). The controller monitors to determine when the oven cavity has reached the oven clean temperature. If the catalyst outlet temperature (T
o
) is not greater than the catalyst inlet temperature (T
i
) before the oven cavity reaches the oven clean temperature, the timer is re-set to a shortened self clean time period (t
s
), less than the full cycle valve and the self clean cycle is terminated when the timer counts down the shortened self clean period.
Additionally, the controller may re-set the timer equal to a run out period (t
ro
), less than the full cycle valve, if the catalyst outlet temperature (T
o
) exceeds the catalyst inlet temperature (T
i
) after the oven clean temperature has been established and then falls below the catalyst inlet temperature (T
i
). In such case, the self clean cycle is terminated when the timer counts down the run out period (t
ro
).
REFERENCES:
patent: 3962561 (1976-06-01), Maitenaz
patent: 4481404 (1984-11-01), Thomas et al.
patent: 4775777 (1988-10-01), Sinn
patent: 4852544 (1989-08-01), Williams et al.
patent: 4954694 (1990-09-01), Nagai et al.
patent: 5026971 (1991-06-01), Payne et al.
patent: 5083010 (1992-01-01), Henry et al.
patent: 5286943 (1994-02-01), Has
patent: 5343020 (1994-08-01), Waigand et al.
patent: 5826520 (1998-10-01), Mainord
patent: 196 06 571 (1997-08-01), None
patent: 878667A2 (1998-11-01), None
Pwu Jeffrey
Rice Robert O.
Roth Thomas J.
Van Winkle Joel M.
Walberg Teresa
LandOfFree
System for controlling a self cleaning oven having catalyst... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System for controlling a self cleaning oven having catalyst..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System for controlling a self cleaning oven having catalyst... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2506157