Electricity: electrical systems and devices – Igniting systems
Reexamination Certificate
1999-07-15
2001-04-24
Fleming, Fritz (Department: 2836)
Electricity: electrical systems and devices
Igniting systems
C361S253000, C361S263000
Reexamination Certificate
active
06222719
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to gas burners such as the type found in gas furnaces, and is more particularly concerned with means for electronically igniting the burner and for detecting or proving the existence of flame after ignition.
A number of electric igniter systems have been proposed for use with gas burners, including igniters that employ a high voltage spark, and igniters that involve a hot surface. In a mobile environment, in which the power for the furnace or heater is derived from a 12 volt DC or a 24 volt DC source, it has been common to employ a spark igniter, as heated surface type igniters have a high failure rate. The spark igniter requires some source of AC or pulsating voltage, and an inverter can be used to generate a wave which is then fed to an ignition transformer. Because of the relatively low voltage available in the mobile environment (i.e., 12 or 24 VDC), the turns ratio of the ignition transformer needs to be quite high. This means that the cost of the transformer is quite high, and also that the transformer can experience inter-turn arcing if fine wire is used in the secondary winding.
In any gas furnace it is mandatory to detect a successful ignition as a safety measure. If gas is permitted to flow to an unlit burner, explosive vapors can fill the dwelling and create a hazardous situation. Accordingly, a flame detection or flame proving means needs to be employed at the gas burner. One simple means for doing this is with a flame rectification probe. This technique is based on the fact that an active flame acts as a plasma diode. A unidirectional current can flow from a probe within the flame to the metal casing of the burner, i.e., the firebox. The flame itself thus acts like a resistance and diode connected in series. By applying an alternating current to the rectification probe, it is possible to detect the presence of flame. Rectification flame proving requires a source of alternating current, but in a mobile environment, where the power comes from 12 or 24 VDC, an inverter or other AC source has to be included in the burner control circuitry. This increases the cost of the circuitry. Moreover, the additional circuit elements increase the risk of failure.
Accordingly, a low cost ignition circuit and a flame detection circuit that would be suitable in a DC control system have been sought without success. A DC furnace control circuit that combines a burner igniter and a flame rectification probe has also been unavailable, without use of an on-board transformer.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of this invention to provide an igniter and rectification flame detection circuit which avoids the drawbacks of the prior art.
It is another object to provide a ignition circuit that employs flyback current from a furnace relay coil to develop a primary ignition current, and which permits the turns ratio of the ignition transformer to be kept relatively low.
It is a further object of the invention to provide a rectification flame detection circuit that derives an alternating current for flame detection from a furnace relay actuator coil.
It is a still further object of this invention to provide a combination burner ignition and flame proving circuit.
According to one aspect of this invention, an igniter circuit for a furnace gas burner employs a pulsating current applied to a relay coil (such as the relay actuator coil for the inducer motor) to generate high flyback voltage. A flyback rectifier has its anode connected to the relay coil and its cathode feeds flyback pulses to a charge storage capacitor arrangement, where the flyback voltage accumulates. A step-up transformer has a primary winding and a secondary winding, with the secondary winding being connected to the igniter. High voltage at the igniter causes arcing to ignite the flame in the gas burner. A hysteresis switch is coupled between the charge storage capacitor and the primary winding of the step-up transformer. When the voltage on the storage capacitor arrangement exceeds some predetermined voltage threshold, e.g., 300 volts, the stored voltage is discharged through the primary winding, and this generates the high voltage arc on the igniter probe. With this arrangement, an intermediate or booster transformer is not needed. Also, this arrangement makes it possible to use an ignition transformer with a relatively low turns ratio, which increases the reliability and reduces the cost.
The charge storage capacitor arrangement can employ only a single capacitor coupled between the diode and a point of DC reference voltage, such as ground. In a preferred embodiment, the capacitor arrangement can be configured as a voltage doubler, with a pair of capacitors and a diode connected in series between points of positive and negative DC voltage
The hysteresis switch can include a controlled switching device, such as an SCR, having main electrodes, e.g., anode and cathode, connected respectively to the diode and to the primary winding of said step-up transformer. A zener device can be positioned between the gate or control electrode and one of the main electrodes of the SCR. A filter capacitor can be connected between the cathode and gate.
According to another embodiment of this invention, a rectification flame detection circuit is constructed for detecting the presence of flame in the burner of the gas furnace. Again, a pulsating current is employed, which is applied to a relay coil (e.g., the gas valve relay) in order to actuate the furnace. A capacitor has one electrode connected to the relay coil, and derives an AC voltage that is used for rectification flame detection. A detection transistor has its gate or control electrode connected through a resistive network to the flame detection conductor, a common or source electrode tied to ground, and a power or drain electrode connected via a signal impedance to a DC source. The drain and signal impedance define an output terminal therebetween. In the resistor network a first resistor has one end connected to the capacitor, its other end being connected to the control or gate electrode of said transistor. A second resistor is connected between the control electrode and common electrode, i.e., ground, of the transistor. The flame detection probe, which is located within the gas burner, is electrically connected to the capacitor and first resistor. In this arrangement, the output of the transistor oscillates between a high state and a low state, e.g., if flame is present, but remains locked in one state, i.e., the low state, if flame is not present in the burner. In a preferred embodiment, the transistor can be a depletion mode FET.
According to a further aspect of the invention, a control circuit combines a gas burner igniter circuit and a rectification flame detection circuit. There are pulsating current signals applied respectively to first and second relay coils in order to actuate the furnace. The combination igniter and flame detection circuit employs a flyback rectifier and charge storage means coupled to the flyback rectifier to accumulate flyback voltage. A step-up transformer has a primary winding and a secondary winding, with the secondary winding being connected to the igniter and flame detection probe to provide a high voltage for generating an arc for ignition. A hysteresis switch is coupled between the charge storage means and the primary winding of the step-up transformer and acts to discharge the current from the charge storage means through the primary winding whenever the stored flyback voltage reaches a predetermined threshold. There is also a capacitor connected to one end of the second relay coil. A flame detection transistor has a signal impedance connected with its drain or power electrode to define an output terminal. A resistor network has a first resistor with one end connected to the capacitor and a its other end connected to the gate or control electrode of the transistor. A second resistor is connected between the gate (control) and source (common) electrodes of the transistor. In t
Fleming Fritz
Molldrem, Jr. Bernhard P.
LandOfFree
Ignition boost and rectification flame detection circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ignition boost and rectification flame detection circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ignition boost and rectification flame detection circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2481442