Abstract:
A simple, highly reliable automatic motor driven oven door latch for an oven self-cleaning operation. To ensure that the motor has operated correctly and has not stopped in a null position, the motor is provided with a start pulse and the location of the latch or locking member of the latching mechanism is monitored to guarantee that the locking member has moved to the correct position. If the locking member has not moved to the correct position, then the motor is provided with another start pulse and the location of the latch or locking member of the latching mechanism again is monitored to again ensure that the locking member has moved to the correct position. This sequence can be repeated on opening and closing of the latching mechanism a desired number of times to guarantee that the locking member has moved to the correct position when locking or releasing the oven door.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to ovens or ranges and, in particular, to a motor driven door latch for self-cleaning ovens or ranges. 
   2. Discussion of the Prior Art 
   So-called self-cleaning or pyrolytic ovens or ranges (hereinafter ovens for simplicity) require high temperatures to burn or vaporize the cooking residues left in the oven chamber. It is conventional to add a locking latch device to the oven to lock the door closed during the self-cleaning operation to prevent accidental or inadvertent opening of the door by a user. In general these latch devices include some type of moving a latch arm into engagement with the oven door to lock the door closed for the self-cleaning operation. The latch device is released upon the completion of the self-cleaning operation, which is generally either time based or based upon the sensed temperature in the oven. 
   One attempt to eliminate this inadvertent opening of the oven door included a manual actuated latch, such as an actuating handle or a lever to rotate the latch to the closed or latched position. There are a number of types of such manual devices and some include bolt type mechanisms. 
   Later attempts to provide the latching mechanism, include various types of automatic or electrically operated motor or solenoid driven latch mechanisms. These mechanisms often are expensive and can be unreliable. Reliability of the locking latch mechanism is of great concern due to the high cleaning temperatures in the oven and consequently also is a UL requirement. 
   It would be desirable to provide an automatic motor driven door latch for an oven, which is simple, inexpensive and highly reliable. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention provides a simple, highly reliable automatic motor driven oven door latch for an oven self-cleaning operation. The present invention also substantially eliminates the danger of a mistaken opening of the oven due to a failed latch operation, which does not fully engage in the locked position. 
   The oven door latch utilizes an asynchronously driven motor for reducing costs in the latching mechanism. To ensure that the motor has operated correctly and has not stopped in a null position, the motor is provided with a start pulse and the location of the latch or locking member of the latching mechanism is monitored to guarantee that the locking member has moved to the correct position. If the locking member has not moved to the correct position, then the motor is provided with another start pulse and the location of the latch or locking member of the latching mechanism again is monitored to guarantee that the locking member has moved to the correct position. This sequence can be repeated on opening and closing of the latching mechanism to guarantee that the locking member has moved to the correct position when opening or closing. 
   The present invention will now be explained in greater detail herein below in terms of an embodiment with reference to the drawings. The drawings illustrate a schematic and diagrammatic representation of the essential components of a motor driven oven door latch, as it can be arranged in an oven according to the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a perspective view of a gas oven in which the motor driven oven door latch of the present invention can be utilized. 
       FIG. 2  illustrates a front plan view of the oven of  FIG. 1  including a schematic illustration of one location of the door latch of the present invention. 
       FIG. 3  illustrates a side plan view of the oven of  FIG. 1  including a schematic illustration of one location of the door latch of the present invention. 
       FIG. 4  illustrates a top plan view of the oven of  FIG. 1  including a schematic illustration of one location of the door latch of the present invention. 
       FIG. 5  illustrates a top plan view of one embodiment of the door latch of the present invention in an unlocked or open position. 
       FIG. 6  illustrates a top plan view of the embodiment of the door latch of  FIG. 5  in a locked or closed position. 
       FIG. 7  illustrates a top plan view of another embodiment of the door latch of the present invention in an unlocked or open position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIGS. 1–4 , a gas oven  10  includes a gas range  12  and an associated control panel  14  for the burners of the oven or range  10 . The type of cooking apparatus, generally referred to as an oven or range is not significant and can be an electric or gas or dual fuel oven (oven is used for ease of reference hereinafter) and a free standing range as illustrated or a built in oven (not illustrated). The oven  10  includes a frame  16 , with an oven chamber  18  in the lower portion thereof below the gas range  12  as is conventional when such a range  12  is included in the oven  10 . The oven chamber  18  is closed by an oven door  20 , which generally includes or can include a window  22  for the user to view the inside of the chamber  18 , such as to view food cooking in the chamber  18 . The operation of the oven chamber  18  is controlled by the user utilizing a second control panel  24 . The self-cleaning operation of the oven chamber  18  is controlled by operation of the control panel  24  as hereinafter described. 
   One central location of the door latch of the present invention, designated generally by a dashed line representation  26  is generally illustrated, not to scale, in  FIGS. 2–4 . The central location  26  is generally the most conventional location for a latch mechanism, generally represented by the reference numeral  30 . (Referring now to  FIGS. 5 and 6  the operation and details of the motor driven oven door latch or latch mechanism  30  (hereinafter door latch) of the present invention is illustrated. The door latch  30  preferably is mounted on a plate or frame  32 , of no particular shape or configuration. The plate  32  then is fixedly mounted (not illustrated) to the oven frame  16  in the location  26 . The oven door  20  is partially illustrated and includes an inner surface or wall  34  shown only as a line for illustration purposes. The inner surface or wall  34  includes a locking slot  36  in a middle region thereof. The door latch  30  includes a latch or lock arm  38  pivotably mounted by a bolt or pin  40  to the plate  32 . The lock arm  38  includes a hook or L-shaped member  42  which is aligned with and movably fits through the locking slot  36  to allow the door  20  to be opened and closed in a non-cleaning mode of operation. 
   When the door  20  is in the closed position, as illustrated in  FIG. 6 , a pin  44  which is biased by a spring  46  into the extended position when the door  20  is open, is depressed by the wall  34  and indicates to the oven  10  that the door  20  is closed. The location of the pin  44  also can conveniently be utilized to operate a light (not illustrated) in the oven chamber  18 , turning on when the door  20  is opened to release the pin  44  and turning off when the door  20  is closed and the pin  44  is depressed. Once this indication is received by the control panel  24 , then the self-clean operation can be initiated by the user. The latch  30  also could include an interlock mechanism, which will not allow the latch  30  to operate unless the door  20  is in the closed position. 
   When the self-clean operation is initiated, the lock arm  38  hook  42  is moved rearwardly and downwardly (as illustrated for reference in  FIGS. 5 and 6 ) to engage an inside edge  48  of the locking slot  36 , as illustrated in  FIG. 6 . This locks the door  20  in a closed position for the duration of the self-cleaning mode of operation. When the operation is ended, the lock arm  38  hook  42  is moved outwardly and upwardly (as illustrated for reference in  FIGS. 5 and 6 ) to release the inside edge  48  of the locking slot  36  to a position where the latch  30  moves freely into and out of the slot  36 , as illustrated in  FIG. 5 . This releases the door for normal opening and closing by the operator. The shape and configuration of the hook  42  is not critical and can vary as desired as long as the locking latch function is maintained by the configuration of the hook  42  and the door edge  48  or other door structure to which the hook  42  will engage. 
   An asynchronously driven motor  50  is mounted to the plate  32  on the opposite side or back side as illustrated in  FIGS. 5 and 6 . The asynchronously driven motor is chosen, because it is very inexpensive, but could be replaced by a DC motor for speed of operation or a stepper motor if desired. A cam  52  made of heat resistant material is molded or otherwise mounted to the motor shaft (not illustrated) and extends through an aperture or opening  54  in the plate  32 . Referring to  FIG. 5 , the unlatched or door released position is illustrated for the door latch  30 . The cam  52  includes an offset arm or hook  56  pivotally mounted to the cam  52  at a first end  58  and pivotally mounted to an opening  60  in the lock arm  38  opposite the hook  42  in a second end  62  of the arm  56 . The open position is monitored by the control panel  24  by the state of a switch  64 . The switch  64  also is selected to meet the necessary temperature rating and can be any type of switch, which provides the required functions. The cam  52  rotates as the motor  50  is actuated and includes a cam portion  68 , which rotates and depresses an actuation pin  66  in the switch  64  when the lock arm  38  is in the fully released or open position. The control panel  24  monitors the switch  64  after the motor  50  is actuated to ensure that the pin  66  is moved to actuate the switch  64  to ensure that the motor  50  is not stuck in a null position. If after actuation the switch  64  is not activated by the pin  66 , then the motor  50  is pulsed again until the switch  64  is activated by the cam surface  68  to guarantee that the latch  30  and the door  20  have been released. 
   When the self-clean operation is initiated, the lock arm  38  is moved into the locked position as illustrated in  FIG. 6  by the rotation of the motor  50  (which in the example illustrated is counter-clockwise). As the cam portion  68  rotates away from the switch  64 , the pin  66  is released and the switch  64  is unactivated. If upon pulsing the motor  50 , the switch  64  remains activated, then the cam surface  68  has not rotated and the motor  50  then is pulsed again. Once the switch  64  is unactivated, then the control panel  24  monitors a second switch  70 , which also has an actuation pin  72  like the switch  64 . Once the pin  72  is depressed by the cam surface  68 , then the switch  70  is activated signalling the control panel  24  that the hook  42  is engaged with the slot edge  48  and the door  20  is locked for the self-cleaning operation. The lock arm  38  can include a bias spring  74  to aid in the rotation of the arm  38 . The motor  50  is energized and then if the switch  64  remains activated, the motor is de-energized for a period and then re-energized to provide a second pulse to the motor  50 . The motor  50  can receive a set number of pulses, such as five (5) before the oven  10  will generate an alarm through the control panel  24  to indicate a motor failure. 
   In another embodiment (not separately illustrated for this description, but see  FIG. 7 ), the self-clean operation also can be accomplished with the door latch  30 , but with only one switch, such as the switch  70  for example. In this embodiment, for example purposes, the door latch  30  includes the same mechanism as illustrated in  FIGS. 5 and 6 , with  FIG. 6  used for descriptive purposes. Again, when the self-clean operation is initiated, the lock arm  38  is moved into the locked position as illustrated in  FIG. 6  by the rotation of the motor  50  (which in the example illustrated is counter-clockwise). The control panel  24  monitors the switch  70  and the actuation pin  72 . Once the pin  72  is depressed by the cam surface  68 , then the switch  70  is activated signalling the control panel  24  that the hook  42  is engaged with the slot edge  48  and the door  20  is locked for the self-cleaning operation. The open position also is monitored by the control panel  24  by the state of a switch  70 . When the self-clean operation is terminated the door latch  30  is released. Once the pin  72  is released from the cam surface  68  as the motor  50  rotates, then the switch  70  is deactivated signalling the control panel  24  that the hook  42  is released from the slot edge  48  and the door  20  is open for regular operation of the oven  10 . 
   Referring to  FIG. 7 , the unlatched or door released position is illustrated for a further embodiment of a door latch  80  of the present invention. While the door latch  30  is placed generally in the central location  26  at the front of the oven  10  adjacent the door  20 , such location is hotter than a more remote location at the rear of the oven  10 , which allows the components of the door latch  80  to be cheaper, since they have a lesser heat rating than the components of the door latch  30 . To accomplish this more preferable location, the latch  80  is still desired to latch the door  20  in the slot  36  in the central location  26 . The active motor and switch elements however are located in a back location of the oven  10  indicated by the dashed line  82 , in  FIGS. 3 and 4 . The latch  80  again includes similar elements to the single switch embodiment just described with respect to the switch  70 . 
   The latch  80  however includes an enlongated plate or frame  82 , such as formed from sheet metal with ribs or upraised edges for structural strength (not illustrated). This allows an active element end  84  to be mounted in the cooler temperature location  82  and a passive element end  86  to be mounted in the front latch location  26 . Also, preferably the plate  82  is mounted at an angle across the oven  10  as illustrated in  FIGS. 4 and 7 . The latch  80  then includes an elongated arm  88  to connect the operative elements in the two locations  26  and  82 . The end  84  includes a switch  90  similar in function to the switches  64  and  70 , but having a lower temperature rating. The switch  90  includes an activation pin  92 , here shown activated by a cam surface  94  of a cam  96 , all similar to the same components in the latch  30 . The cam  96  is mounted to a shaft  98  of a motor  100  mounted on the opposite side of the plate  82  adjacent an aperture or opening  102 . 
   The arm  88  is pivotably mounted to the cam  96  at a first end  104  and at a second end  106  to a lock arm  108 . The lock arm  108  has a hook  110  which latches to the edge  48  in the slot  36  as the arm  108  is rotated in a direction A, in the same manner as the hook  42  of the lock arm  38 . The lock arm  108  is pivotally mounted to the plate  82  by a pin or bolt  112 . The lock arm  108  also includes a clearance slot  114 , which allows the arm  108  to move relative to the pin  112  as the arm  88  rotates the arm  108 . 
   In the latch  80  embodiment, as illustrated in  FIG. 7 , the self-clean operation again can be accomplished with only the one switch  90 . In this embodiment, when the self-clean operation is initiated, the lock arm  108  is moved into the locked position by the arm  88  by the rotation of the motor  100  (which in this embodiment is counter-clockwise). The control panel  24  monitors the switch  90  and the actuation pin  92 . The pin  92  is depressed by a leading edge  116  of the elongated cam surface  94  to activate the switch  90  at the end of a self-cleaning operation. The cam  96  rotates counter clockwise when the self-clean operation is initiated. As the arm  88  is moved by the rotation of the cam  96 , the switch remains activated and the latch or lock arm  108  rotates in the direction A until it locks the door  20  shut by engaging the hook  110  with the edge  48  of the slot  36 . The locking movement of the latch  80  is completed at the same time as a trailing edge  118  of the cam surface passes the pin  92  and then the switch  90  is de-activated signalling the control panel  24  that the hook  110  is engaged with the slot edge  48  and the door  20  is locked for the self-cleaning operation. The open position also is monitored by the control panel  24  by the state of a switch  90 . When the self-clean operation is terminated the door latch  80  is released. The cam  96  is rotated again past a cam surface  120  between the edges  116  and  118 , which does not engage the pin  92 . Once the pin  92  is re-activated by the cam surface  94  at the leading edge  116  as the motor  50  rotates, then the pin  92  is depressed and the switch  90  is activated signalling the control panel  24  that the hook  110  is released from the slot edge  48  and the door  20  is open for regular operation of the oven  10 . The lock arm  108  can include a bias spring  122  to aid in the rotation of the arm  108 . 
   Having thus generally described the present invention, the same will become better understood from the appended claims in which the present invention is set forth in a non-limiting manner.