Combustion – Process of combustion or burner operation – Starting or shutdown procedure
Reexamination Certificate
2001-06-01
2003-06-03
Bennett, Henry (Department: 3743)
Combustion
Process of combustion or burner operation
Starting or shutdown procedure
C431S012000, C431S070000
Reexamination Certificate
active
06572363
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to furnaces, and particularly to detecting flame rollout in furnaces.
2. Technical Background
Flame rollout is a phenomenon that occurs when a heat exchanger is blocked, the blower compartment is leaking into the heat exchanger, combustion air is deficient, or when flue gas re-circulates into the combustion air stream. When flame roll-out occurs, the flame generated by a gas burner does not emanate inwardly toward the furnace's heat exchanger. Instead, the flame is pulled outwardly into the cabinet of the furnace. Flue gas is recirculated when the flue pipe is somehow removed.
Typically, furnaces include a manual reset temperature actuated flame rollout switch that detects unacceptably high bumer assembly temperatures. It will halt heating operations and will not allow the furnace to resume heating operations until the switch is reset. If a flame rollout condition causes a loss of flame sense before the normally closed manual reset temperature actuated flame rollout switch can open, the furnace will attempt to re-ignite the gas burners to continue heating operations. If repeated flame rollouts of this type occur within a short period of time, an undesirable build up of flue gasses may result.
What is needed is a system for tracking repeated occurrences of loss of flame sense due to flame rollout after successful burner ignition. An ignition is deemed to be a successful ignition if ignition continues to be proved and the gas valve continues to supply the burner with gas for a predetermined amount of time after the ignition of the gas burners. Most of the transient causes of flame loss occur within approximately 70 seconds of elapsed time from the moment of ignition. Thus, when flame sense is lost after 70 seconds of burner operation, it is highly probable that the cause is flame rollout. A method is needed to lockout the furnace after repeated occurrences of lost flame sense due to flame rollout. Lockout would continue for three hours to assure that the undesirable gas build-up dissipates.
SUMMARY OF THE INVENTION
The present invention addresses the above stated problem. The present invention is directed to a system and method for detecting loss of flame sense due to flame rollout in a furnace. The furnace of the present invention includes a flame proving sensor disposed near a gas burner. The flame proving sensor transmits a flame proving signal to a processor when it detects a flame emanating from the gas burner. The present invention tracks repeated incidents of lost flame sense due to flame rollout occurring after successful ignitions of the gas burners. The present invention performs a furnace lockout if three such incidents of flame rollout occur within a predetermined period of time, usually one-hour.
One aspect of the present invention is a method for controlling a furnace. The furnace includes a gas valve, at least one gas burner, and a flame proving sensor. The flame proving sensor is operative to supply the furnace with a flame proving signal when a flame is detected in the at least one gas burner. The method includes performing a furnace lockout when the flame proving signal is lost during each of a predetermined number of heating cycles within a predetermined period of accumulated gas burner on-time. A heating cycle is a period of gas burner flame detection time that is greater than or equal to a first predetermined period of time.
In another aspect, the present invention includes a method for controlling a furnace. The furnace includes a gas valve, at least one gas burner, and a flame proving sensor. The flame proving sensor is operative to supply the furnace with a flame proving signal when a flame is detected in the at least one gas burner. The method includes the steps of actuating the gas valve to an on-state to thereby provide gas to the at least one gas burner. The gas is ignited to thereby produce a flame emanating from the at least one gas burner. The flame proving sensor is checked after the gas valve has been in the on-state for a predetermined amount of time. The gas valve is actuated to an off-state when the flame proving sensor fails to detect a flame in the previous step. The previous steps are repeated twice. Finally, a furnace lockout is performed when all of the previous steps are performed within a second predetermined period of time. The furnace ignores requests for heat during the furnace lockout.
In yet another aspect, the present invention includes a system for detecting flame rollout in a furnace. The furnace includes a gas valve and at least one gas burner. The system includes a flame proving sensor disposed proximate the at least one gas burner, the flame proving sensor being operative to detect a flame emanating from the at least one gas burner. A processor is coupled to the flame proving sensor, the processor being programmed to execute a furnace lockout when the flame proving signal is lost during each of a predetermined number of heating cycles within a predetermined period of accumulated gas burner on-time.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.
REFERENCES:
patent: 4337893 (1982-07-01), Flanders et al.
patent: 4516510 (1985-05-01), Basic, Sr.
patent: 4789330 (1988-12-01), Ballard et al.
Thompson Kevin
Virgil, Jr. Hall
Bennett Henry
Carrier Corporation
Wall Marjama & Bilinski LLP
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