Electricity: electrical systems and devices – Control circuits for electromagnetic devices – For relays or solenoids
Reexamination Certificate
1999-12-09
2001-11-27
Huynh, Kim (Department: 2836)
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
For relays or solenoids
C361S247000, C361S168100
Reexamination Certificate
active
06324046
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to control and actuator circuits for furnaces or similar gas burning equipment. The invention is more specifically concerned with a driver circuit for a gas valve will actuate a dual-solenoid gas valve in a fashion that will fail-safe when one component of the gas valve fails or sticks. The invention is also concerned with a circuit that actuates two or more solenoids from a single controller output.
In a modern gas furnace, one or more gas burners inject a gas flame through a heat exchanger, and the combustion gases are drawn through the heat exchanger by means of an inducer blower, which exhausts the combustion gases to a vent or flue. A pressure sensor associated with the inducer actuates a pressure switch to indicate a pressure differential between the exhaust and intake of the inducer. The pressure switch provides assurance that the inducer is functioning properly. There is also a flame sensor which is intended as a means for shutting the gas valve off if flame does not appear in the burner after some limited period of time.
An indoor air blower forces air from a comfort zone past the heat exchanger to draw heat from the combustion gases. The warmed air is then returned to the comfort zone. A temperature limit switch on the heat exchanger is normally closed, and opens if the heat exchanger exceeds a predetermined temperature. This limit switch serves as a check on proper air flow and functioning of the indoor air blower.
A thermostat located in the comfort zone closes when the room temperature drops below a predetermined setpoint, and thereby signals a call for heat. When a call for heat is detected, control and timing circuitry for the furnace actuates the inducer blower and then initiates an actuation sequence which energizes a gas valve relay so that current is supplied to the gas valve. This allows combustion gas to flow to the burners. At this time, igniters are actuated to light the burners, and the furnace begins to produce heat. An infrared detector, rectification or other mechanism is employed to ensure that there is flame after the gas valve is actuated. If no flame is present, another series switch interrupts the thermostat power and turns off the gas valve. Also, a rollback switch detects if flame is not entering the heat exchanger but is instead proceeding in the combustion air intake direction.
After the burners have been ignited for a predetermined time, the room air blower is powered up, and this creates a flow of warm air to the interior comfort zone.
Conventionally, 24 volt thermostat power, either AC or DC, is supplied through the series arrangement of the limit switch, thermostat, pressure switch, gas valve relay, and gas valve.
As aforementioned, the limit switch, thermostat, and pressure switch are all disposed in series with the gas valve relay, so that no current can flow through the gas valve relay to actuate the gas valve, until the limit switch and pressure switch are both closed. This serves as a check that the room air blower and the inducer blower are functioning properly.
A safety problem can arise if any of the limit switch, pressure switch, or gas valve relay are for some reason locked into a closed condition. In those cases, the gas valve will continue to feed gas to the burners if the heat exchanger experiences overtemperature, or if the inducer fails to produce sufficient draft.
This problem, and a solution to it, are described in Kadah U.S. Pat. No. 5,917,691 and in Kadah et al. U.S. Pat. No. 5,889,645.
Generally, whenever there is a call for heat, the controller should be able to check the conditions of the pressure switch and the gas valve relay before supplying current to the coil for the gas valve relay. This permits the control circuit to check for switch malfunction and indicate a service condition, if service or repair is required.
The gas valve relay has a pair of actuator coils, and these are generally connected in parallel. A gas valve driver circuit is controlled by an output of the microprocessor and supplies drive current to both coils. Each solenoid has an associated gas valve mechanism, and these are connected in series on the gas line so that both valve mechanisms have to open for gas to reach the burner. This is intended as a safety measure, and to ensure that one of the gas valves will close if, for some reason, the other sticks in the open position. Also, the gas valve relay driver circuit is typically designed so that if any of the driver components fail, the gas valve will not turn on. These safety features are necessary to keep the room space around the furnace from flooding with unignited gas, as that could present a danger of either suffocation or explosion. Normally, the two solenoids are tied together, so that the driver feeds both of them at the same time. However, an additional safety feature can be obtained by driving one of the two solenoids directly, and the other indirectly. In that way, if the first solenoid or its driver fuses or is locked up, the second solenoid will fail to actuate, i.e., will not turn on its associated gas valve mechanism. Unfortunately, no one has previously configured a gas valve driver to do this.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of this invention to provide a fail-safe drive system for a gas valve or other device which will takes advantage of the dual-solenoid construction of the gas valve and avoids the drawbacks of the prior art.
It is another object to provide a dual-solenoid drive circuit that is actuated from a single output of a microprocessor or other controller circuit.
It is a further object of the invention to utilize flyback voltage from the actuation of the first solenoid for energizing the second and further solenoids.
According to an aspect of this invention, an actuator circuit is configured for electrically actuating a dual-solenoid gas valve, of the type in which a first solenoid and a second solenoid are both energized to open the gas valve to supply a gas burner for a furnace or other gas-powered appliance. In the actuator circuit of this invention, a controller circuit selectively provides output pulses at an output terminal. These output pulses can have a first state at which pulses are present (i.e., pulsating) and a second state in which pulses are absent (i.e., steady high or steady low). A transistor or other switch device has its base, gate or similar control electrode coupled to the output terminal of said controller circuit, and has its collector, drain, or similar output electrode connected to the first solenoid to supply drive pulses to it. A flyback-driven relaxation oscillator circuit has an input coupled to the junction of the first solenoid and the output electrode (e.g., collector) of the switch transistor, so as to receive flyback voltage from the first solenoid. An output of the oscillator circuit is connected to second solenoid and provides drive pulses to the second solenoid. In a preferred arrangement, the flyback-driven relaxation oscillator circuit is formed of a diode or similar rectifier having one electrode coupled to the junction of said first solenoid and said switch transistor, and an accumulator capacitor connected to a second electrode of said rectifier to accumulate said flyback voltage. A negative resistance device or similar discharge device is connected between the accumulator capacitor and the second solenoid to discharge energy from said capacitor into said second solenoid when the accumulated flyback voltage has risen to some threshold. The controller arrangement typically may be a microprocessor device, but the arrangement could be based on a multivibrator circuit, a PUT based circuit, or a logic circuit used in place of the microprocessor.
The relaxation oscillator circuit may be configured as a voltage doubler arrangement, with a voltage doubler connected between the above-mentioned junction and the second solenoid. In that case, the flyback-driven relaxation oscillator circuit is formed with a capacitor and diode connected between the juncti
Huynh Kim
Molldrem, Jr. Bernhard P.
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