Abstract:
An apparatus is provided for controlling a fuel fired heating appliance, the apparatus comprising a first processor for controlling the ignition operation of the furnace and a second processor for controlling the operation of a variable speed blower motor, wherein the first processor sends communication signals to the second processor requesting a desired speed of the blower motor to provide air flow for combustion. The second processor responsively sends a signal to the first processor indicating the receipt of the requested speed for the blower motor. The apparatus further comprises at least one pressure switch, where the first processor senses an opening of the pressure switch and responds by successively sending incrementally higher speed request signals to the second processor until the first processor detects the closing of the at least one pressure switch.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention is generally related to fuel-fired heating appliances, and more specifically to the control of a variable speed blower motor in a variable heating fuel-fired appliance.  
         [0002]     Many fuel-fired appliances that provide variable heating rates utilize a variable speed motor to drive a blower fan for establishing air flow for combustion. Manufacturers of such heating appliances typically utilized an ignition control module to control the ignition operation of the appliance, and a separate motor processor module to control the variable speed blower motor. These prior art systems relied on the ignition control module to send a high or low speed signal, or alternatively a pulse-width modulated signal to the motor processor, which accordingly had to be configured to interpret the signal and establish the desired speed. The ignition controls of these prior art systems typically had no feedback from the motor processor, and relied on a pressure switch to determine if the desired blower flow rate had been established. If the blower speed was not sufficient to close the pressure switch, the ignition control could only request an incremental increase in speed without any feedback from the motor processor. HVAC systems accordingly relied on two separate controllers for system operation, in which an ignition processor could not verify whether the motor processor had received a speed request signal or whether the motor controller was even functioning.  
       SUMMARY OF THE INVENTION  
       [0003]     The present invention relates to an apparatus for controlling a fuel fired heating appliance, the apparatus comprising a first processor for controlling the ignition operation of the furnace and a second processor for controlling the operation of the blower motor, wherein the first processor sends communication signals to the second processor which responsively establishes the desired speed of the blower having a variable speed blower motor to provide air flow for combustion. After the first processor sends a communication signal to establish a blower speed, the second processor sends a communication signal to the first processor indicating a receipt of the requested speed of operation. The first processor of the apparatus is also capable of detecting the closing of at least one pressure switch, and responsively signals the second processor to increase the speed of the blower motor until the first processor detects the closing of the at least one pressure switch. The closure of a pressure switch verifies the blower motor has established a desired air flow for combustion, and subsequently switches power to an igniter to establish burner operation.  
         [0004]     In accordance with one aspect of the present invention, the apparatus can provide for two-way communication between the first and second processors, in which the first ignition processor may request information from the second motor processor pertaining to the voltage level between line and neutral. This voltage value may be evaluated by the first processor prior to supplying power to the igniter, such that a desired power level is provided that will allow the igniter to ignite gas without being unnecessarily overheated. In some embodiments, the apparatus therefore prolongs the life of the igniter and the operation of the appliance.  
         [0005]     In another aspect of the present invention, the apparatus can provide for verification of communication from the first ignition processor to the second motor processor. In the event that the second motor processor is not responding to the first processor, the first ignition processor can communicate a reset signal to reset the second motor processor and reestablish communication with the second motor processor.  
         [0006]     In yet another aspect of the present invention, the apparatus can provide for communication of diagnostic information between a first ignition processor and a second motor processor, and also for communication of diagnostics. In some embodiments, the apparatus further provides a means of communication via a single output to a first device or a second device, by switching from a first mode of communication to a first diagnostic reporting device, to a second mode of communication to a second motor processor device. In some embodiments, the second motor processor may communicate diagnostic information to the first ignition processor, which may then communicate to a multi-color flashing LED to provide an optical transmission of diagnostic information. This method of communication provides a simple, reliable means of controlling operation of the motor processor as well as a means of providing diagnostic information. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is schematic diagram of one embodiment of an apparatus according to the principles of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]     One embodiment of an apparatus for controlling a fuel-fired appliance according to the principles of the present invention is illustrated in  FIG. 1 , and comprises a first ignition processor  22  and a second motor processor  24 . The apparatus comprises connection means for various appliance components including a thermostat  26 , a blower motor  28 , a pressure switch  30 , an igniter  32  and a gas valve  34 . The first ignition processor  22  is connected to a half-wave regulated 5 volt power supply, which is supplied by a 24 vac power source  40 . The 5 v power supply comprises a diode  42  and a zener diode  46  in series with a voltage regulator  48 , and also a capacitor  44 . The second processor for the blower motor is connected to a separate power supply (not shown) that is supplied by a 120 vac power source  50 . The circuitry for the first processor and second processor are electrically isolated from each other within the apparatus. The apparatus includes connection means for connecting the apparatus to a three-phase blower motor  28 , and a pressure switch  30 . When receiving a request signal for heating from the thermostat  26 , the first processor  22  for controlling the ignition operation may signal the second processor  24  to request the blower motor  28  to ramp up to a desired speed. When the desired level of air flow is established by the blower motor  28 , the pressure switch  30  will close. The first ignition processor  22  monitors the closure of the pressure switch  30  to verify sufficient air flow is present for combustion, before switching power to an igniter  32  for igniting the supply of fuel. When the igniter  32  has been sufficiently warmed up, the first ignition processor  22  outputs a signal to activate the gas valve  34  to initiate the supply of gas to be ignited.  
         [0009]     The ignition processor  22  of the present invention is preferably a ST72C334 microprocessor manufactured by ST Microelectronics. The ignition processor controls the start of the blower motor  28  by first establishing communication with the motor processor  24 . The ignition processor  22  provides a high enable signal from a communication enable pin at  82  to gate a transistor  86  to a conductive state, which switches 5 volts to a light-emitting diode of an opto-isolator  90 . The ignition processor  22  generates a 9600 baud rate serial bit stream signal at  84  from a data port, such as a Universal Asynchronous Serial Port (UART). The serial transmission signal gates transistor  88  on and off, which intermittently shunts the high enable signal away from transistor  86 , to allow transistor  86  to switch the opto-isolator transistor  90  on and off. The serial bit stream signal output from the opto-transistor  90  is input to the second motor processor  24 , which receives the signal requesting the blower motor  28  be ramped up to a desired speed to establish air flow for combustion.  
         [0010]     The second processor  24  of the present invention is preferably a Digital Signal Processor ADMCF328 manufactured by Analog Devices. The second processor  24  receives the signal from the first processor, and subsequently measures the line-to-neutral voltage and generates three sine wave forms  106  from a 170 VDC source using a power module  108 . The power module  108  in the present invention is preferably a IRAMS10UP60 manufactured by International Rectifier. The three rectified sine wave outputs are connected to the blower motor  28 , and are varied in frequency and voltage amplitude to control the speed of the blower motor. The use of rectified variable frequency drive circuits for controlling motor speed is well known in the art, and will not be covered in detail.  
         [0011]     As the blower motor  28  ramps up to the desired speed predetermined by the first ignition processor  22 , the ignition processor  22  monitors the closure of a pressure switch  30 . If the pressure switch  30  does not close, the ignition processor  22  sends a request signal for an incrementally higher speed to the motor processor  22 . Upon closure of the pressure switch  30 , the first ignition processor  22  stores the last requested speed value at which the pressure switch closed. The ignition processor  22  may then request this speed in subsequent cycles for establishing a desired blower motor speed. The second motor processor  24  responds by outputting a serial bit stream signal to the first ignition processor  22 , signaling the receipt of the requested speed signal, and responsively changes the speed of the blower motor. In the event the Digital Signal Processor, or second motor processor  24 , locks up and does not respond to the first ignition processor  22 , the first ignition processor transmits a signal to the second motor processor at a reduced baud rate to prompt a reset of the second motor processor  24 . In particular, a reset circuit monitors the transmission signal output from the opto-transistor  90  at node  92 . The reduced baud rate transmission causes the UART port to be held low for a long enough period to exceed the time constant of the resistor-capacitor circuit  98 , so as to reduce the voltage input to the inverting pin of an op-amp  96 . A non-linear op-amp circuit configured as a comparator is used to determine when the transmission signal voltage to the inverting pin drops below a reference voltage to the non-inverting pin, and responsively provides an output voltage that gates a transistor  102  to shunt a 5 v signal away from the second motor processor  24  for resetting the processor.  
         [0012]     The first ignition processor  22  may also request the second motor processor  24  to transmit the value of the voltage between line and neutral. This value may then be used by the first ignition processor  22  to determine an on-off sequence for switching line voltage to the igniter that will power or heat up the igniter to a level sufficient to ignite gas, without overheating the igniter. Specifically, the first ignition processor determines a switching rate based on the line voltage value received from the second motor processor, and drives a transistor  58  to gate an opto-triac switch  60  on and off. The opto-triac  60  drives a triac  62  for switching line voltage  50  through a filter  52  to the igniter  32 . With the closed pressure switch  30  indicating sufficient air flow and the igniter  32  heated up, the ignition processor  22  drives transistors  70  and  72  for switching a pair of redundant relays  74  and  76  to a closed position to actuate the main valve  36  of the gas valve  34 . This initiates the supply of gas to the igniter  32 , to establish flame for a first heating rate. When receiving a request signal for a higher stage of heating from thermostat  26 , the first ignition processor  22  transmits a signal to the second motor processor  24  requesting an increase in blower motor speed to establish a higher air flow for combustion. The higher blower speed may close a second pressure switch (not shown) to indicate sufficient air flow is present for the higher combustion rate. The first ignition processor  22  then drives a transistor  78  for switching a relay  80  to activate the second stage valve  38  of the gas valve  34 .  
         [0013]     The first ignition processor  22  is capable of transmitting a serial data stream at a first baud rate to the second motor processor through a single data port, which is also used to transmit data at a second baud rate to a flashing LED. When the ignition processor  22  provides a high enable signal, the transmitted data intended for the second motor processor is not seen by the flashing LED. When the enable pin is high at  82 , transistor  112  shunts the transmission signal  84  away from the gate of transistor  114  to prevent switching of the LED  116 . Likewise, when the enable pin is low at  82 , the transistor  86  is non-conductive to prevent communication to the second motor processor  24 , while a second 4800 baud rate signal at  84  is used to switch transistor  110  on and off to intermittently shunt 5 v away from transistor  114 , for switching 5 volts on and off to the flashing LED  116  in the event that communication with the second motor processor is lost or cannot be restored, or in the event that the blower motor has been diagnosed by the second motor processor to be inoperable, the first ignition processor can provide a diagnostic signal to the Light port LED. This provides for optical transmission of diagnostic information related to the blower motor or fuel fired appliance to a service technician. The first ignition processor  22  may also communicate diagnostic information relating to a malfunctioning pressure switch, ignition error, flame roll-out, or other error.  
         [0014]     It should be noted that the method of switching the enable signal for providing communication via a signal data port to a first or second device may be used for devices other than a flashing LED. A third microprocessor could also receive communication from the first ignition processor. Likewise, if two way communication is required with the third microprocessor, the receive port could be multiplexed in a similar manner to allow both the second motor processor and the alternative third microprocessor to communicate via a single receive port on the first ignition processor  22 .  
         [0015]     Additional design considerations, readily apparent to one of ordinary skill in the art, such as modification of the apparatus to provide an output signal for a modulating gas valve for varying the supply of fuel to enable an infinitely variable heating appliance, may also provide improved appliance operation. It should be apparent to those skilled in the art that various modifications such as the above may be made without departing from the spirit and scope of the invention. More particularly, the apparatus may be adapted to any of a variety of different gas fired appliances including gas clothes dryers and furnaces. Accordingly, it is not intended that the invention be limited by the particular form illustrated and described above, but by the appended claims.