Abstract:
Improved lockout control in oil primary controllers for oil heating systems which allows a reasonable number of user resets and ignition retries in the event of lockout, while minimizing the unwanted accumulation of oil in the combustion chamber of the heating system. When the oil primary goes into lockout mode due to failure of combustion to take place, the oil primary is placed in a restricted mode of operation in which a limited number of reset activations and combustion retries may be attempted. If they are unsuccessful, a waiting time interval is then imposed between further successive attempts. The lockout or trial for ignition time may also be reduced for subsequent attempts, to minimize flooding. Normal operation is returned once a successful combustion cycle has been achieved.

Description:
BACKGROUND OF THE INVENTION 
     The invention pertains to oil primary controls for oil-fired heating systems, and in particular, to an improved lockout mode control for an oil primary. 
     Oil heating systems employ a control, referred to generally as an oil primary, which controls the delivery of a fuel oil/air mixture and ignition spark to the combustion chamber of the oil burner. Such systems also use a combustion or flame detector, usually a photosensor, to detect when combustion has successfully begun. This is necessary because, for a number of reasons, it is possible that an attempted ignition may not result in combustion. Such factors include a complete or partial loss of fuel or air, loss of ignition source, or clogged or failed component in the oil burner. One function of the oil primary is to interrupt the flow of oil to the combustion chamber if successful combustion is not detected within a certain time period, which is often referred to as the lockout time or the TFI (trial for ignition) time. If combustion is not confirmed within the lockout time, the oil primary shuts off the flow of oil and air, and igniter spark, and places the system in lockout mode. In lockout mode, the system will no longer respond to a call for heat from a thermostat, which it would do, of course, in a normal mode of operation. 
     Normally, manual intervention is required to take the system out of lockout mode, either by a service person or by the homeowner/user. A reset button is provided in association with the oil primary to allow user activation of a reset input. Alternatively, it is envisioned that suitable intervention may be provided remotely via a communication link. Since it is possible that the problem which caused the lockout may self-correct, the reset gives the opportunity of successfully starting the oil heating system again. If the restart attempt is successful, it avoids the inconvenience and expense of a service call, and in the worst case, may avoid the prospect of frozen or damaged pipes in the home. 
     However, if the root problem which caused the lockout has not cleared or is not fixed, a reset will cause another attempted oil ignition cycle, and result in a further lockout. In many instances a homeowner may continue to push the reset button, in an attempt to restart the system. In cases where the system does not clear or correct itself, this will result in flooding of the combustion chamber with unignited oil. This might create a hazard, and may require a service person to come to the site and clean out the combustion chamber, which is a time consuming and costly process. Because of these problems, prior oil primaries, such as the Model R7184 Interrupted Electronic Oil Primary commercially available from Honeywell International Inc., have generally provided a limitation on the reset function, for example, limiting it to three times without successful ignition, after which the system remains in lockout and a service person must be called. This approach has the disadvantage, however, that if service is not readily available during cold periods, occupants may not be able to continue living in the space to be heated, and under certain. circumstances, damage may result due to freezing water pipes. 
     SUMMARY OF THE INVENTION 
     The present invention improves on the lockout control of the prior art by allowing flexibility and a greater number of user resets and ignition retries in the event of lockout, while still minimizing the unwanted accumulation of oil in the combustion chamber. 
     According to the present invention, if lockout occurs due to failure of combustion to take place, the oil primary is placed in a restricted mode of operation in which a limited number of reset activations may be attempted. If they are unsuccessful, a waiting time interval is imposed between successive attempts, and optionally the lockout time is also reduced for such subsequent attempts, to minimize flooding. Normal operation is returned once a successful combustion cycle has been achieved. 
     According to the present invention, there is provided an oil primary for initiating and controlling oil combustion in an oil heating system, normally in response to a thermostat or Aquastat® signal indicating a call for heat. An ignition detector, such as a Model C554A Cadmium Sulfide Flame Detector commercially available from Honeywell International Inc., provides an indication to the oil primary of whether or not combustion has been achieved in the oil heating system. If combustion is not detected within the lockout time period, oil is shut off and the system is placed in lockout mode. A user reset is provided for receiving user reset inputs, which release the lockout mode to permit the oil primary to retry combustion. In the event of a number of such retries without successful combustion, the system imposes a waiting interval before permitting a further retry in response to a user reset activation. 
     According to another feature of the invention, after a number of unsuccessful retries, the lockout time period is reduced, to reduce the amount of oil introduced into the combustion chamber on each retry, to further reduce the possibility of oil flooding. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawing, 
     FIG. 1 is a schematic diagram of a control system including an oil primary for an oil burner, of the type to which the present invention may be advantageously applied; and 
     FIG. 2 is a flowchart of restricted lockout control according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, an oil burner appliance is shown, including a combustion chamber identified by reference numeral  10 . It receives fuel oil from a line  11  from a fuel oil source (not shown), through a pump  12 , line  13 , valve  14  and line  15 . This is representative of certain oil burner appliance designs. Other designs do not include a valve corresponding to valve  14 . 
     An oil primary  20  is provided for controlling the ignition and combustion process. Oil primary  20  receives signals on control line  21  when there is a call for heat to the system. Typically, this is provided by a thermostat or Aquastat® which is indicated at reference number  22 . Alternatively, other types of devices could be used for calling for heat, such as a user-activated switch, a timer-activated switch, or the like. 
     An igniter  30  is provided, which may be part of the oil primary, or a separate device controlled by the oil primary, as is the case in FIG.  1 . Igniter  30  is connected at lead  31  to the oil burner appliance, to provide an ignition spark to initiate a combustion cycle. Igniter  30  operates under control of oil primary  20 , via the indicated control line  23 . Oil primary  20  also controls a motor  16 , which drives pump  12  and a blower  17 , as indicated, via control line  24 . An ignition detector  18  is also provided, positioned to view the flame area within combustion chamber  10 , and connected via control line  25  to oil primary  20 . Ignition detector  18  may be a Honeywell C554A Cadmium Sulfide Flame Detector. 
     In normal operation for a heating cycle, oil primary  20  receives a signal, for example, from thermostat or Aquastat®  22 , calling for heat. In the system shown in FIG. 1, oil primary  20  first energizes igniter  30  to initiate ignition spark, and then energizes motor  16 , which activates pump  12  and blower  17 . Thereafter, oil primary  20  supplies a signal over a control line  19  to open valve  14 , which introduces fuel oil into the air stream produced by blower  17  to supply oil mist to combustion chamber  10 . During a lockout time interval, the oil primary checks for confirmation from ignition detector  18  on control line  25 , that acceptable combustion has been achieved. If so, the burn continues through the normal combustion cycle. 
     However, if during the lockout time the successful establishment of combustion has not been achieved, the oil primary goes into lockout mode. In this mode igniter  30 , motor  16  and valve  14  are de-energized, thereby terminating the supply of spark, air and oil mist. The oil primary, while locked out, and will not respond to further signals calling for heat, without a manual reset intervention. 
     As indicated in FIG. 1, oil primary  20  includes a user-actuatable reset input, commonly in the form of a reset button  26  connected to a switch. Activation of reset button  26  takes the oil primary out of lockout mode, permitting a retry of a combustion cycle. If successful, the combustion cycle proceeds normally. If, however, the retry is not successful, which will most likely be the case if the root cause of the combustion failure has not cleared or been corrected, another lockout will result. The user, typically a homeowner, might activate reset button  26  a number of times trying to reestablish operation of the heating unit. In existing systems, this may cause a significant amount of oil to accumulate in the combustion area, degrading it and ultimately requiring a maintenance service call for cleaning. 
     Because of this, some prior art oil primaries have limited the number of resets to a small number, typically three retries. If no successful combustion cycle takes place during the three retries, the system remains locked out, necessitating a service call. 
     The present invention improves upon the prior art by providing a lockout with a restricted user reset capability, which provides the opportunity to restart the system if possible, but which limits the amount of oil accumulation and subsequent degradation of the combustion chamber, if unsuccessful. 
     Oil primaries may be implemented in different technologies, including relays, discrete or integrated electronic logic, programmed microcontrollers, or various combinations thereof. Likewise, the lockout-reset control of the present invention can be implemented in any of those or other known technologies. 
     The embodiment of the invention disclosed herein with reference to FIG. 2 is in the form of software routines to work in conjunction with a microcontroller-based oil primary. The basic operating steps of the oil primary described above are generally known, and are not covered in FIG.  2 . FIG. 2 represents a flowchart of the restricted lockout control for the oil primary. 
     The program of FIG. 2 is shown as beginning at flow arrow  50 , which would represent a branch from the main control of the oil primary (not shown) at the beginning of a combustion cycle. Step  51  is the trial for ignition initiation. At step  52 , the system tests whether the trial for ignition was successful. A successful test is when the photocell or flame detector confirms that combustion has been established within the lockout time. Typically, the default or factory setting for lockout time would be 45 seconds, although other times for the lockout could easily be selected. In the event of a successful test, control branches to flow path  53  to step  54 . At this step, the trial counter (discussed below) is reset to zero, the lockout time is reset to the default or factory settings, and normal operation is continued for a combustion cycle. At this point, the control exits the loop of FIG. 2, and would return to the main control (not shown) of the oil primary. 
     If the trial for ignition was not successful at decision block  52 , control passes through path  55  to step  56 . At this point, an increment is added to a trial counter within the programmed microprocessor, which is used to keep track of the number of combustion retries. Concurrently, the control enters the lockout state, which requires manual reset before the ignition process can be reinitiated. A wait timer, used in step  69  below, may also be set at this point. The trial counter and lockout status are stored in a nonvolatile memory associated with the microcontroller for the oil primary. The reason for using nonvolatile memory is so that in the event there has been a power outage, or the user disconnects power to the oil primary and then reconnects it, the lockout status and count of number of trials will be preserved. 
     From step  56 , control passes via path  57  to a decision block  60 . This block loops back on path  61  waiting to detect a user reset activation. When the user pushes the reset button or otherwise provides a reset activation, control passes to path  62 . Path  62  leads to decision block  63 , which checks the trial counter to determine the number of trials since the start of the current non-combustion situation. If this is a first trial, control passes via path  64 . If there are two trials, control passes via path  65 , and if there have been more than two trials, control passes via path  66 . 
     In the event of a first trial, path  64  takes control to step  70 , which causes clearing of the lockout status from nonvolatile memory, but not clearing of the count in the trial counter. Control then proceeds via path  71  back to the start of the trial for ignition. Thus, a retry is enabled. If the retry is successful, as detected at decision block  52 , control will pass out block  54 , resetting the trial counter to zero as it will no longer be needed. If, however, the trial was not successful, control passes via path  55  to increment the trial counter, and if the reset button is pressed, eventually leads to decision block  63  again. 
     If there have been two trials, meaning two attempts, the initial attempt and one reset-retry, control will pass to step  67 . At this point, the lockout time is reduced to a shorter interval than the original. For example, if the default or factory setting is 30 seconds, the reduced lockout time may be shortened to, for example, 10 seconds. This is to further reduce the amount of oil accumulation in the event of a further unsuccessful retry. Control then passes via path  68  to block  70  and so on, as previously described for a further retry. 
     If at decision block  63 , the number of trials has exceeded two, control passes to decision block  69 . At decision block  69 , the wait timer is queried to determine whether the wait time has expired since the start of the last retry. The wait time may be set at, for example, 1 hour, although other longer or shorter times may also be used. If the wait time has not expired, control loops back via path  73  to await a reset actuation at step  60 . However, as long as the wait time has not expired, the control will be stalled in the loop including decision block  69 , effectively preventing a further retry. 
     If the wait time has expired, control passes via path  72  to block  67 , and eventually back to trial for ignition block  51 , as previously described. 
     The operation of the embodiment of FIG. 2 is illustrated in the example shown in the following table. Six trials are shown in the example, the initial thermostat-initiated ignition trial, and five user reset-initiated samples. Note that after trial number 2, the lockout time is reduced from 30 seconds to 10 seconds, which still gives sufficient time to confirm successful combustion, but which if unsuccessful, reduces the total amount of oil accumulation. Note that after trial number 3, a one hour wait is imposed before each successive user-initiated retry, thus further limiting the oil accumulation if the retries are unsuccessful. In this example, six trials were attempted with a total accumulation time of 100 seconds of oil flow, spread out over a period of three hours. By comparison, a prior art lockout control as described above would permit three tries, or 135 seconds of oil, which might all happen within just a few minutes. 
     
       
         
               
               
               
             
           
               
                   
               
               
                   
                   
                 Total Oil 
               
               
                 Trial 
                 Trial for Ignition Time 
                 Accumulation Time 
               
               
                   
               
             
             
               
                 #1 
                 30 seconds 
                 30 seconds 
               
               
                 #2 
                 30 seconds 
                 60 seconds 
               
               
                 #3 
                 10 seconds 
                 70 seconds 
               
               
                 One Hour Wait 
               
               
                 #4 
                 10 seconds 
                 80 seconds 
               
               
                 One Hour Wait 
               
               
                 #5 
                 10 seconds 
                 90 seconds 
               
               
                 One Hour Wait 
               
               
                 #6 
                 10 seconds 
                 100 seconds  
               
               
                   
               
             
          
         
       
     
     It will thus be appreciated that the restricted lockout control of the present invention reduces the amount of accumulated oil in the case of a nonfunctioning burner, while at the same time allowing or permitting restart of the burner should the cause of the shutdown correct or clear itself. 
     It will be seen from the above that the present invention provides an improved oil primary lockout control and method of operation for allowing a reasonable number of user resets and ignition retries in the event of lockout, while still minimizing the unwanted accumulation of oil in the combustion chamber. While specific embodiments of the invention have been described, it will be appreciated that the invention is not limited to those specific applications, and that many variations are possible within the scope of the invention.