Abstract:
An improved self-cleaning oven ( 10 ) is provided having an assembly ( 12 ) to control the cleaning cycle time of the oven ( 10 ) depending upon the degree of oven contamination and soil present therein. The assembly ( 12 ) includes a measuring chamber ( 16 ) as well as a passageway ( 18 ) communicating the interior ( 14 ) of the oven ( 10 ) and the chamber ( 16 ). A smoke detector ( 32 ) (preferably an infrared smoke detector) is associated with the chamber ( 16 ) and is coupled with a controller ( 20 ) so as to measure a parameter of smoke passing through the chamber during at least a portion of the cleaning cycle. This parameter is then used to determine the proper duration of the cleaning cycle. In preferred forms, measuring chamber ( 16   a ) is equipped with an ambient air inlet ( 52 ) and outlet ( 54 ) so as to draw an ambient air stream through the chamber ( 16   a ) between the smoke detector ( 32 ) and the oven gas stream.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is broadly concerned with improved self-cleaning ovens including an assembly to control the duration of the high-temperature oven cleaning cycles. More particularly, the invention pertains to such ovens, cycle controlling assemblies and methods wherein a parameter of at least a portion of the smoke generated during an oven cleaning cycle is measured and the duration of the cleaning cycle is determined in response to such measurement. 
     2. Description of the Prior Art 
     Many household and industrial ovens are equipped with self-cleaning cycles. When an oven is soiled, the user initiates a cleaning cycle, which involves heating of the oven to a very high temperature (e.g., 800° F.) so as to sublimate the oven contaminants. Conventional cleaning cycles operate for a preset period of 2-4 hours so as to insure that all such contaminants are removed from oven surfaces. During the course of a cleaning cycle, smoke is generated as the contaminants char and are sublimated. Usually the period of greatest smoke is during the initial thirty minutes or so of a cycle. Thereafter, smoke production tails off and becomes less prevalent. 
     A problem with conventional self-cleaning ovens is that the cleaning cycle is conducted for a preset period, regardless of the amount of soil and contaminants in the oven. Thus, the same amount of high temperature operation is carried out for a heavily or lightly soiled oven. This not only unnecessarily takes the oven out of service for longer than may be necessary, but also wastes significant energy. 
     There is accordingly a need in the art for improved self-cleaning ovens which will terminate an oven cleaning cycle after different periods of heating, in a manner commensurate with the level of soil and contaminants in the oven. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the problems outlined above and provides an oven cleaning cycle time-controlling assembly for use with self-cleaning ovens. The cycle time-controlling assembly of the invention operates by measuring a parameter of at least a portion of the smoke generated during an oven cleaning cycle, and by ascertaining the appropriate cycle duration in response to such measurement. 
     The preferred controlling assembly of the invention includes a sensing chamber together with a delivery system (e.g., a passageway) communicating the oven interior and the sensing chamber in order to convey at least a portion of the smoke evolved during the cleaning cycle to the sensing chamber. A smoke detector is associated with the sensing chamber in order to measure the smoke parameter of interest. Advantageously, the smoke detector is a conventional infrared smoke detector which is coupled with an electronic controller, in order to measure the a parameter of smoke generated during at least a portion of the cleaning cycle. 
     An on-off valve may be interposed within the delivery system between the oven and chamber and is also coupled with the controller. During normal oven usage, the valve is closed so as to prevent passage of oven gas to the measuring chamber. The valve is opened during the course of the cleaning cycle to allow passage of oven gas and smoke to the measuring chamber. Also, an in-line smoke filter may be interposed in the delivery system to remove the largest smoke particles. This reduces the rate of smoke contamination of the sensor chamber and other components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a self-cleaning oven with the preferred cleaning cycle time-controlling assembly of the invention coupled thereto; 
     FIG. 2 is a schematic view illustrating the preferred construction of the measuring chamber forming a part of the cleaning cycle time-controlling assembly; 
     FIG. 3 is a schematic representation of the preferred measuring chamber, equipped with spaced openings for drawing ambient air through the measuring chamber during use thereof; and 
     FIG. 4 is a graph of smoke intensity versus time for a typical soiled oven and illustrating the preferred technique for determining the cleaning cycle duration time. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, FIG. 1 illustrates an oven  10  in combination with the cleaning cycle time-controlling assembly  12  of the invention. Broadly speaking, the oven  10  is itself conventional and presents an interior  14 . The oven  10  is of the self-cleaning variety which is controlled by conventional control and timing electronics. The assembly  12  includes a measuring chamber  16  as well as a delivery system  18  which communicates oven interior  14  and the chamber  16 . A controller  20  also forms a part of the assembly  12 . 
     In more detail, the measuring chamber  16  is preferably molded from high temperature-rated synthetic resin materials and is in the form of small tubular or box-like enclosure  22  presenting exterior walls  24  as well as an oven gas inlet  26  and an opposed oven gas outlet  28 . The chamber  16  is equipped with a sensor  30  in the form of an infrared smoke detector  32 . The detector  32  includes an infrared light emitting diode (LED)  34  as well as a spaced infrared detector  36 . The LED  34  and detector  36  are placed within the enclosure  22  and are oriented so that smoke passing through the chamber  16  will be detected. As illustrated in FIG. 2, these components are angularly disposed relative to each other so that infrared radiation emitted by LED  34  will be scattered by the smoke (usually containing solid particles and various types of volatile organic compounds (VOCs)), and a portion of such scattered radiation is detected by the detector  36 . 
     It will be understood that the enclosure  22  illustrated in the drawings is of simplified design. In practice, the enclosure may simply be of tubular configuration with a diameter similar to that of the tube  46 , so that the volume of the enclosure is less than that of the delivery system  18 . Also, the chamber may include provision for preventing LED radiation from reaching the IR detector when there is no smoke within the enclosure. Such may include special wall shapes, internal partitions, or IR black coating on the interior of the chamber. Also, the enclosure may have provision for verification for smoke sensor performance, such as a special opening that allows insertion of a calibrated scattering media (such as a simple piece of plastic or fabric) instead of smoke. 
     The controller  20  is connected to the LED  34  and detector  36  for control thereof. Specifically, the controller is electrically coupled to an infrared LED driver  38 , and the output of the latter is connected to LED  34 . An amplifier  40  and analog-to-digital converter  42  are connected in series between the detector  36  and controller  20  as illustrated. The main range controller  44  which is connected to and controls oven  10  is also connected to the controller  20 . 
     The delivery system  18  is preferably in the form of an elongated metallic tube  46  which is connected to oven  10  and to input  26  of the enclosure  22 . An on-off valve  48  is interposed within tube  46  between oven  10  and chamber  16 . The valve is also coupled with controller  20  which controls the on-off operation thereof. 
     Turning next to FIG. 3, a modified measuring chamber  16   a  is illustrated. In this case, enclosure  22  includes the oven gas inlet and outlet  26 ,  28  with the tube  46  coupled to the former. An exhaust tube  50  is connected to oven gas outlet  28 . In this instance however, the enclosure  22  is also provided with a pair of opposed openings  52 ,  54  which are an ambient air inlet and an ambient air outlet respectively. The openings  52 ,  54  are located between the oven gas inlet and outlet  26 ,  28 , and the sensor  30 . 
     During normal use of oven  10  for the baking of foods and the like, assembly  12  does not come into play. That is, the valve  48  remains closed so that oven gases cannot pass through tube  46  to chamber  16 . However, when it is desired to clean oven  10  using the self-cleaning cycle thereof, initiation of the cycle through the main range controller  44  also initiates operation of controller  20 . When this occurs, the valve  48  is opened at a predetermined time, thereby allowing oven gas and a portion of the smoke generated as a result of the cleaning cycle to pass through the tube  46  and thus into and through the chamber  16 . During passage of the oven gas and smoke through the chamber  16 , the smoke detector  32  is operated via controller  20  so as to repeatedly measure the smoke intensity over a period of time. In preferred practice, the quantity of smoke is measured during the initial phase of the oven cleaning cycle, which generates most of the smoke which will be evolved during the cycle. For example, the smoke intensity within chamber  16  during an initial period of the cleaning cycle may be used for controlling the time of the cleaning cycle. 
     In more detail, it will be understood that the smoke detector  32  measures a signal proportional to light scattered from the smoke within the chamber  16 . Data is acquired by iteratively measuring the output signal of the IR detector  36  as I(i), typically every 10 seconds after the cleaning cycle is initiated. In the first step, a I(i) baseline is determined by measuring the detector output signal during the initial no smoke stage of the cleaning cycle. When the detector  36  senses a low predetermined threshold of smoke SO, a time t 1  is noted and a series of smoke intensity S(i) determinations are made. These S(i) values are calculated using the equation S(i)=C×(I(i) measured−I(i) baseline), where C is a scaling coefficient, and I(i) measured is the detector value obtained at each measurement time. These S(i) values are determined until an S(i) value falls below the threshold SO, this being noted as time t 2 . The S(i) values obtained during the time period between times t 1  and t 2  are used to calculate the scattered signal power P, which is the average of the S(i) values determined between t 1  and t 2 . Using the scattered signal power P, the duration of the cleaning cycle time T can be obtained either from a lookup table or using the polynomial function: 
       T=a   0 + a   1 × P+a   2 × P   2 + a   3 × P   3 +. . . 
     where a 0 , a 1  and a 2  are predefined polynomial coefficients. The power of the polynomial is variable but in the typical case is 3. 
     FIG. 4 is a graphic illustration of the preferred technique for measuring S(i) in order to ultimately calculate the duration of cleaning cycle time. As illustrated, during the initial no-smoke period, a baseline of zero is established by the described iterative measurements. After the detector  16  begins to detect smoke and S(i) exceeds the predefined threshold SO, additional measurements of S(i) are iteratively made (e.g., every 1 second) until S(i) falls below the SO threshold. Thereupon, the S(i) values between t 1  and t 2  are averaged to obtain P, and P is used to determine the cleaning cycle duration time. In the FIG. 4 illustration, the threshold SO is set at an S(i) value of approximately 1200, the scaling coefficient C is 1, and the polynomial coefficients are a 0 =−538, a 1 =0.040527273, a 2 =−5.272727E-07 and a 3 =0. It is anticipated that in actual practice the scaling coefficient C will be selected so that the value P is equal to 1 at maximum scattering signal. 
     After the smoke measurement period has elapsed, the controller  20  operates to close valve  48  and also informs the main range controller  44  of the time at which the cleaning cycle is to terminate. Thus, when the oven  10  is heavily soiled, copious amounts of smoke are generated during the t 1 -t 2  measurement period, thus leading to a longer cleaning cycle duration. Of course, when the oven  10  is less soiled, a smaller quantity of smoke will be generated during the t 1 -t 2  period, and a correspondingly shorter cycle time will be used. 
     Where the FIG. 3 sensor  16   a  is used, ambient-derived air is drawn by convection through opening  52  and along the length of the chamber to and through opening  54 . This stream of ambient air is located between the sensor  30  and the oven gas and smoke passing through the sensor. Inasmuch as these flows are essentially laminar in nature, there is very little intermixing of the oven gas and ambient streams. The use of an ambient air stream is this fashion serves to protect the sensor  30  from smoke contamination and buildup of residues thereon. 
     Those skilled in the art will appreciate that the invention is subject to many possible variations. For example, the measuring chamber may be specially sized or configured for a particular oven and cleaning duty. Furthermore, while an infrared smoke detector is preferred for reasons of cost and availability, any other type of known smoke detector could be employed. While the controller  20  is shown as separate from the main range controller  44 , it will be understood that the electronics for the controlling assembly  12  may be built into the main range controller itself. 
     It may also be desirable to add a filter in the line  46  to separate heavy grease and oil components from the smoke entering chamber  16 . This will prevent sensor contamination while still allowing smoke to enter the chamber. Furthermore, while the exhaust from the chamber  16  is shown as a tube  50 , this may be replaced by one or more holes in the chamber body.