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  Pilot tube assembly and method for gas appliance rangesUSPTO Application #: 20060286497Title: Pilot tube assembly and method for gas appliance ranges Abstract: A pilot tube assembly comprises a gas inlet tube and a pilot tip with a central aperture. During delivery of gas, one or more apertures of the assembly aspirate ambient air to provide a combustible mixture. A central tapered bore of the assembly receives a gas inlet tube. The tapered bore of the pilot tip is swaged with a gas inlet tube by application of force. The taper angle of central tapered bore ranges from about 1 to 2 degrees, and is preferably 1.5 degrees, with respect to the center line of the pilot tip to enable swaging action at reasonable pressures and to enable a large thermal contact area between the pilot tip and gas inlet tube, thereby equilibrating their temperatures and preventing separation due to thermal expansion. (end of abstract) Agent: Ernest D. Buff Ernest D. Buff And Associates, LLC. - Bedminster, NJ, US Inventor: John M. Tursky USPTO Applicaton #: 20060286497 - Class: 431278000 (USPTO) Related Patent Categories: Combustion, Separately Supplied Or Controlled, Physically Related Flame Holders, E.g., Diverse Fuels, Pilot And Main, Etc. The Patent Description & Claims data below is from USPTO Patent Application 20060286497. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] This application claims the benefit of Provisional Application No. 60/691,895, filed Jun. 17, 2005. [0002] 1. Field of the Invention [0003] The present invention relates to a pilot tube assembly for gas appliances, including gas ranges, gas furnaces, gas grills and other gas fired appliances wherein the pilot line ignites the main gas flame. [0004] 2. Description of the Prior Art [0005] Pilot tubes are used in gas appliance ranges and stoves. The pilot tube is an assembly of a gas inlet tube of carbon steel fuel line, having one end attached to a special fitting called a pilot tip. This attachment needs to be free from gas leakage even when the pilot tube is subjected to repeated cycles of varying temperature. An assembly comprised of a pilot tip and a gas inlet tube is commonly referred to as a pilot tube assembly. The pilot tube assembly provides a continuous flame that is always available for the lighting of a range burner. [0006] There are over ten major stove and range manufacturers in the US and across the world, all of which require a pilot tube assembly for safe operation. Stove and range manufacturers have essentially adapted one of three commonly accepted methods for manufacture of pilot tube assemblies. Those methods commonly used to manufacture pilot tube assemblies include: a) compression fitting assembly; b) brazing assembly; and c) deformation assembly. Each of these three prior art assembly methods and their disadvantages are discussed. [0007] The prior art compression fitting assembly of pilot tubes uses compression fittings. A threaded pilot tip is connected to a brass compression sleeve having a brass compression nut carried by the gas inlet tube, as illustrated at 10 in the photographs shown in FIG. 1. The FIG. 1 photographs show the pilot tube assembly both in the opened-out configuration and the assembled configuration. The pilot tip is threaded at one end 11. It is connected to the gas inlet tube using industrial brass compression sleeve 12 and nut 13. The assembled pilot tube assembly is shown on the photograph to the right. This assembly operation is manual and time consuming and the machined components, including the threaded pilot tube, are very expensive. The connection of the gas inlet tube to the pilot tip compresses the compression sleeve 12 by the nut 13, with the result that misalignment therebetween results in gas leakage. The gas tube has to be thrown away since it is deformed by the compression fitting, which is permanently deformed over the gas inlet tube. [0008] The prior art brazing assembly of the pilot tube assembly is illustrated at 20 in the photographs of FIG. 2. A machined fitting slid over the gas inlet tube is positioned at the end of the pilot tip and the parts are brazed together using a braze filler. The braze filler fills the gap between the gas inlet tube and the machined fitting as well as the gap between the machined fitting and the end of the pilot tip. The brazed joint is shown at 21. During brazing, movement of the parts or non-uniform braze fill in either of the two joint locations, may result in gas leakage. The machined fitting and the brazing operation of pilot tube assembly components are inherently expensive, whether the operation is carried out manually or in an automated fashion. [0009] The prior art deformation assembly of the pilot tube assembly is illustrated at 30 in the photographs of FIG. 3. A loose fitting pilot tip fitting 31 is placed on the end of a pilot tip. Using a chisel-type devise, the pilot tip is deformed onto the gas inlet tube. The left photograph shows the loose pilot tip fitting 31 slid over the gas inlet tube 32. The right photograph shows the deformed pilot tip creating a pilot tube assembly. The deformation location of the pilot tip is shown at 33. This deformation process tends to be unreliable. Manufacturers using this assembly method report that a high percentage of fittings become loose and fall off, causing concern in the gas range industry. [0010] U.S. Pat. No. 4,854,855 to Rajewski discloses a flare igniter assembly. The flare igniter assembly comprises an elongated tubing assembly including a first air supply conduit and a fuel gas supply line enclosed inside the first air supply conduit. The fuel gas supply line is provided with a member having a venturi-type orifice through which fuel gas and intake air pass. The orifice effects the initial mixing of fuel gas and air. The fuel gas supply line further includes a combustion zone and means for transferring a fuel gas-air mixture downstream from the orifice to the combustion zone. The combustion zone includes an inspirating baffle member firmly positioned within the fuel gas supply line. The terminal portion of the fuel gas supply line extends into the second air supply conduit, within which an ignited flame is burning. The second air supply conduit is adjacent to a porthole in the flare stack, near the upper end thereof, to ignite combustible waste gases passing through the flare stack. The disclosed flare igniter assembly is a waste gas igniter. The construction method of the igniter involves the use of a venturi in the gas line to aspirate air from the second air tube, which surrounds the gas tube. The air is not aspirated from the ambient and there is no pilot tip in this device. [0011] U.S. Pat. No. 6,814,570 to Zink, et al. discloses a venturi mixer and combustion assembly. The combustion assembly includes a venturi mixer and a combustion tip, which is attached to a discharge end section of the venturi mixer. The discharge end section of the venturi mixer is provided with a divergent interior wall. Because of the reduction in pressure drop at the venturi exit, the device is able to induce more combustion air. Thus, the premix gas burner tip or pilot tip/burner is capable of operating over a wider air to fuel ratio range. Further, the flame propagation speed increases as a result of the induction of more combustion air with increased flame stability. The gas inlet tube has an orifice and the venturi mixer is placed in front of the gas inlet tube. It is not bonded to the gas inlet tube in any manner. The gap between the gas exit tube with the orifice and the venturi mixer is critical and is not controlled. [0012] U.S. Pat. No. 5,716,003 to Streetman discloses a jet pilot tip. The jet pilot tip is adapted for use in an in-line connection of a fuel supply. The jet pilot tip includes a body with a threaded bore, which is capped during use, and an open surface with a side conduit member connected to a fuel supply line. The cap is removed and a pin is inserted to clean the nozzle of the jet pilot tip. Gas is injected out of the jet pilot tip into the ambient. The pilot tube does not mix gas and air to create a readily combustible fuel air mixture. [0013] There remains a need in the art for a pilot tube assembly that functions reliably in gas appliances. Also needed is a manufacturing process for producing a low cost pilot tube assembly in an automated assembly operation. Gas leaks in the pilot tubes are undesirable and result in safety concerns. Since the pilot tube is always turned on and the main gas flame impinges on the pilot tube, its construction must repeatedly withstand severe thermal cycles without failure. SUMMARY OF THE INVENTION [0014] The present invention discloses a pilot tube assembly that is economical to manufacture and provides an extremely reliable joint between the pilot tip and the gas inlet tube. The pilot tube assembly does not require compression fittings, brazing operations, or operations that deform the pilot tip, which make conventional pilot tube assemblies less reliable to manufacture and shorten their service live. [0015] The pilot tip has a central aperture to deliver gas and later apertures to aspirate ambient air. The gas stream and air stream are mixed and delivered to the tip of the pilot tube assemble to create a continuous stable pilot flame. The pilot tip is provided with a taper in a central bore that is intended to join with the gas inlet tube. The diameter of the tapered bore at the gas inlet tube entry point is slightly larger than that of the gas inlet tube's outer diameter. The bore entry point may be as large as 1.005 to 1.05 times the outer diameter of the gas inlet tube. The assembly machine forces the pilot tip onto the gas inlet tube and the two pieces swage-lock together. This intimate connection between the pilot tip and the gas tube inlet has several key embodiments. For this swaging process to occur, the taper angle has to be selected within a narrow range, in order to be operable within a certain pressure range applied by the assembly machine. The gas inlet tube deforms to match the taper that is present in the pilot tip. A smaller taper angle allows this swaging operation to occur at a lower pressure, provides large contact area between the pilot tip interior surface and the gas inlet outer surface. The gas inlet tube also travels a larger distance into the pilot tip. If the angle is larger, the reverse holds true. When the angle exceeds a certain value, it is practically impossible to force the gas inlet tube into the tapered bore of the pilot tip since plastic deformation of the gas inlet tube outer surface is incapable of accommodating the deformation required. Experiments with various taper bore geometry of the pilot tip have resulted in the selection of a rather narrow range of taper angles that result in the reliable swaging operation. A taper angle of 1 to 2 degrees from the centerline, preferably 1.25 to 1.75 degrees, and more preferably 1.5 degree, provides optimum swage lock bonding. [0016] The selection of the angle of taper affects the swaged part in several key aspects. First, it determines the distance that the gas inlet tube penetrates into the pilot tip. The assembly machine has to be designed to provide the force over this displacement distance for reliable swaging. Secondly, the angle also determines the contact area between the gas inlet tube and the pilot tip. Since the main gas flame impinges on the pilot tip, its temperature rises causing the pilot tip to expand. If the gas tube is not in intimate contact with the pilot tip, it has a lower temperature than the pilot tip, causing the loosening of the joint between the pilot tip and the gas inlet line. Intimate contact between the two components results in smooth heat flow, keeping their thermal expansions similarly matched, thereby maintaining intimate contact even when the assembly is thermally cycled. The pilot tip may be cast and machined to required dimensions and this operation is conducted at a minimal cost since no threading is needed. The assembly machine uses a standard gas inlet tube and swages the two components together reliably by the application of selected pressure and distance of movement using an air cylinder ram. The assembly process allows for semi-automatic assembly and greatly reduces labor costs. [0017] Significant advantages are realized by practice of the present invention. Key features of the pilot tube and method therefor include, in combination, the components set forth below: [0018] 1) a pilot tip has apertures for aspirating air attached to a gas inlet line providing a gas air mixture that permits reliable combustion to produce a continuous flame capable of igniting a main gas flame in a reliable manner, while sustaining multiple thermal duty cycles; [0019] 2) the pilot tip is provided with a tapered inlet end to receive the gas inlet tube; [0020] 3) the taper is in the range of 1 to 2 degrees from the centerline, preferably 1.25 to 1.75 degrees, and more preferably 1.5 degrees; [0021] 4) the gas inlet tube is forced into the tapered bore of the pilot tip by the application of pressure from an air cylinder ram in an assembly machine, thereby swaging, deforming and mechanically locking the gas inlet tube into the pilot tip by deformation of the outer surface of the gas flow tube and thereby producing the pilot tube assembly; and [0022] 5) the intimate contact between the gas flow tube's outer surface and the pilot tip's inner surface transmits heat from the main gas flame, maintaining approximately equal thermal expansion of the pilot tip and gas inlet tube, thereby permitting multiple thermal cycles of the pilot tube assembly; Continue reading... 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