Patent Publication Number: US-2020284429-A1

Title: Blower assembly for gas-burning appliance

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 62/813,394 filed Mar. 4, 2019 for BLOWER ASSEMBLY FOR GAS-BURNING APPLIANCE, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The field of the disclosure relates generally to blower assemblies for gas-burning appliances, and more specifically to a blower assembly including a two piece housing. 
     Known gas-burning appliances require sufficient airflow to exhaust, and to reduce the concentration of, dangerous combustion gas by-products, such as, for example, CO (carbon monoxide), NO 3 , and NO 4 , among others. In some known high efficiency furnaces, water heaters, and other gas-burning appliances, standard chimney air-draw effects are not sufficient to assure the required airflow through the gas burners and heat exchangers, and therefore, some known gas-burning appliances utilize draft inducers to provide sufficient airflow through the heat exchangers of the furnace and to reduce the concentration of combustion by-products. The generated airflow is typically drawn in from ambient or through an inlet duct by a blower, and typically exhausted through an exhaust duct. Blowers installed in gas-burning appliances are typically selected to operate at a sufficient speed and volume to generate the necessary airflow for efficient heat transfer within the appliance and to exhaust combustion gases with an acceptable by-product concentration. 
     BRIEF DESCRIPTION 
     In one aspect, a blower assembly for a gas-burning appliance is provided. The blower assembly includes a blower and a motor coupled to the blower and configured to turn the blower to provide airflow through the gas-burning appliance. The blower assembly also includes a housing enclosing the blower and the motor. The housing includes a first portion and a second portion coupled to the first portion. The first portion and the second portion define a cavity therebetween to receive the motor and the blower. The blower assembly further includes an inlet sleeve coupled between the first portion and the second portion. The inlet sleeve is configured to couple to the gas-burning appliance and receive the airflow from the gas-burning appliance. The blower assembly also includes a seal extending at least partially around the inlet sleeve and at least partially between the inlet sleeve and at least one of the first portion and the second portion. 
     In another aspect, a gas-burning appliance is provided. The gas-burning appliance includes an inlet to receive airflow into the gas-burning appliance and a burner configured to carry out combustion of the airflow and a fuel. The gas-burning appliance also includes a heat exchanger configured to receive airflow from the burner and facilitate transfer of heat from combustion gases in the airflow to a medium. The gas-burning appliance includes a vent duct configured to receive airflow from the heat exchanger. The gas-burning appliance also includes a blower assembly including a blower and a motor coupled to the blower and configured to turn the blower to provide the airflow through the gas-burning appliance. The blower assembly also includes a housing enclosing the blower and the motor. The housing includes a first portion and a second portion configured to couple to the first portion. The first portion and the second portion define a cavity therebetween to receive the motor and the blower. The blower assembly also includes an inlet sleeve coupled between the first portion and the second portion of the housing. The inlet sleeve is configured to couple to the vent duct and receive the airflow from the vent duct. 
     In yet another aspect, a. method of assembling a blower assembly for a gas-burning appliance is provided. The method includes coupling a housing first portion to a housing second portion. The housing first portion and the housing second portion define a cavity therebetween to receive a motor and a blower. The motor is configured to turn the blower to provide airflow through the gas-burning appliance. The method also includes coupling an inlet sleeve between the housing first portion and the housing second portion. The inlet sleeve is configured to receive the airflow from the gas-burning appliance. The method further includes positioning a seal at least partially around the inlet sleeve and at least partially between the inlet sleeve and at least one of the housing first portion and the housing second portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially schematic perspective view of an exemplary embodiment of a gas-burning appliance with a portion of an enclosure of the gas-burning appliance cut-away to illustrate interior components of the gas-burning appliance; 
         FIG. 2  is a perspective view of a blower assembly for use with the gas-burning appliance shown in  FIG. 1 ; 
         FIG. 3  is a perspective view of the blower assembly shown in  FIG. 2  with a portion removed to show a blower and a motor; 
         FIG. 4  is a top view of the blower assembly shown in  FIG. 3 ; 
         FIG. 5  is an enlarged sectional view of an inlet sleeve of the blower assembly shown in  FIGS. 2-4 ; and 
         FIG. 6  is an enlarged sectional assembly view of a portion of a seal of the blower assembly shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “example implementation” or “one implementation” of the present disclosure are not intended to be interpreted as excluding the existence of additional implementations that also incorporate the recited features. 
     Gas-burning appliances, such as, for example, and without limitation, furnaces and water heaters, burn a mixture of air and a fuel to generate heat that is carried by combustion gasses. The combustion gasses are typically drawn through a heat exchanger by a blower, and then vented out through an exhaust duct. While flowing through the heat exchanger, the combustion gasses heat another medium, such as, for example, water. If the airflow is too little, combustion gasses are inadequately evacuated from the gas-burning appliance and dangerous CO gas can result. If the airflow is too great, combustion gasses are properly vented, but the combustion and heat exchange become less efficient due to excess air being pulled through the burner. 
     Embodiments of the present disclosure provide a blower assembly for gas-burning appliances. More specifically, embodiments of the blower assembly described herein include a fan, a motor connected to the fan to turn the fan, and housing enclosing the blower and the motor. The housing is assembled using a two-piece construction and includes a first portion and a second portion. The first portion is coupled to the second portion such that the first portion and the second portion define a cavity to receive a motor and a blower. In addition, an inlet sleeve is coupled between the first portion and the second portion and is configured to couple to a vent duct of the gas-burning appliance for receiving combustion gases from the gas-burning appliance. The inlet sleeve may be formed separately from the first portion and the second portion or may be integrally formed with one of the first portion and the second portion. A seal extends around the inlet sleeve and at least partially between the inlet sleeve and at least one of the first portion and the second portion. 
     The blower assemblies described herein are less expensive to assemble that at least some known blower assemblies for gas-burning appliances. For example, embodiments of the blower assembly described herein include two portions that couple together to form the housing. An inlet sleeve is coupled between the two portions. As a result, the housing is simpler to assemble and requires less time to assemble and install than at least some known blower housings. In addition, the housing encloses both the fan and the motor and reduces the noise of the blower assembly during operation of the blower assembly. 
     The blower assemblies are more compact and provide a reduced profile that is simpler to install than prior systems. For example, the housing encloses all components of the blower assembly and reduces the total number of components of the blower assembly. Moreover, auxiliary systems such as a motor cooling system are incorporated into the blower assembly. As a result, the separate systems/components of the blower assembly can be constructed with less expensive components and do not require separate housings. 
       FIG. 1  is a partially schematic perspective view of an exemplary gas-burning appliance  100 . Gas-burning appliance  100  includes a tank  102 , a fuel supply  104 , an inlet  106 , a burner  108 , a heat exchanger  110 , a vent duct  112 , a blower assembly  114 , and an exhaust duct  116 . Blower assembly  114  includes a blower  132  (shown in  FIG. 3 ) and a motor  134  (shown in  FIG. 3 ) for turning blower  132 . Gas-burning appliance  100  may further include a control system to control components of gas-burning appliance  100  such as burner  108 , fuel supply  104 , and/or blower assembly  114 . In alternative embodiments, gas-burning appliance  100  includes any components that enable gas-burning appliance  100  to operate as described herein. 
     An airflow  118  is drawn through gas-burning appliance  100  by blower assembly  114 . Airflow  118  is drawn into gas-burning appliance  100  at inlet  106 . Airflow  118  exits gas-burning appliance  100  at exhaust duct  116 . Although blower assembly  114  is shown as positioned proximate exhaust duct  116 , it is contemplated that blower assembly  114  may be located at any position along airflow  118 . For example, blower assembly  114  may be located upstream of burner  108  such that blower assembly  114  pushes air through burner  108  rather than pulling air through burner  108 , as is shown in  FIG. 1 . 
     Gas-burning appliance  100  includes an enclosure  122  within which certain components of gas-burning appliance  100  are disposed. Burner  108 , heat exchanger  110 , and blower assembly  114  are located within enclosure  122 . Enclosure  122  includes tank  102  which defines an interior space  124 . Tank  102  is configured to hold a medium such as water within interior space  124 . Tank  102  may include an inlet and an outlet for the medium to flow into/out of tank  102 . Heat exchanger  110  extends through interior space  124  and contacts the medium within interior space  124 . Burner  108  is positioned below tank  102  within a lower enclosure portion  126  of enclosure  122 . Lower enclosure portion  126  includes inlet  106 . Blower assembly  114  is positioned within an upper enclosure portion  128  located above tank  102 . In alternative embodiments, one or more of burner  108 , heat exchanger  110 , and blower assembly  114  may be located outside enclosure  122 . For example, in some embodiments, upper enclosure portion  128  is omitted and blower assembly  114  is positioned outside enclosure  122 . 
     Airflow  118  enters gas-burning appliance  100  at inlet  106 . Airflow  118  is generated by the turning of impeller  140  (shown in  FIG. 3 ) by motor  134  (shown in  FIG. 3 ) to draw inlet airflow  118  into enclosure  122 . Burner  108  carries out combustion of airflow  118  and a fuel provided by fuel supply  104 , producing combustion gasses that include a proper amount of CO 2  and only trace amounts of CO. Combustion gasses pass through heat exchanger  110 , where heat is transferred from the combustion gasses to another medium, such as, for example, and without limitation, water, within interior space  124  of tank  102 . Airflow  118  carries the combustion gasses from heat exchanger  110 , through vent duct  112 , through blower assembly  114 , and through exhaust duct  116 . Combustion gasses in airflow  118  are vented from exhaust duct  116  out of gas-burning appliance  100 . 
       FIG. 2  is a perspective view of blower assembly  114  for use with gas-burning appliance  100 .  FIG. 3  is a perspective view of blower assembly  114  with a portion removed to show blower  132  and motor  134 . Blower assembly  114  includes a blower  132 , a motor  134 , and a housing  136 . In the exemplary embodiment, blower  132  includes an impeller  140  including a plurality of radially extending, curved vanes  142 . Motor  134  is coupled to blower  132  by a shaft  138  (shown in  FIG. 4 ) and is configured to turn impeller  140  to provide airflow  118  through gas-burning appliance  100  (shown in  FIG. 1 ). In alternative embodiments, blower assembly  114  includes any blower  132  that enables blower assembly  114  to operate as described herein. 
     In the exemplary embodiment, motor  134  rotates shaft  138  to cause rotation of impeller  140 . Motor  134  may be any motor that enables blower assembly  114  to operate as described herein. Accordingly, housing  136  is modular and configured to receive different types of motors because of the construction of housing  136  described herein. For example and without limitation, housing  136  is configured to receive C-frame motors, shaded pole motors, permanent split capacitor (PSC) motors, and electronically commutated motors (ECM). 
     Also, in the exemplary embodiment, housing  136  encloses blower  132  and motor  134 . Housing  136  includes a first portion  144  and a second portion  146 . Housing  136  has a clamshell configuration and is assembled by coupling first portion  144  to second portion  146 , which collectively form the entire body of housing  136 . As a result, the time required to assemble housing  136  is reduced in comparison to housings that require three or more parts to enclose a motor or blower. Moreover, housing  136  may be constructed using less expensive materials and methods than at least some known housings. Also, housing  136  may be assembled and installed at the installation site relatively quickly and without the use of specialized tools or parts. 
     In addition, in the exemplary embodiment, first portion  144  and second portion  146  define a cavity  148  therebetween to receive motor  134  and blower  132 . Also, first portion  144  and second portion  146  may include saddles or other features to support and align first portion  144  and second portion  146 . First portion  144  and second portion  146  completely enclose motor  134  and blower  132  when motor  134  and blower  132  are positioned within cavity  148 . Accordingly, blower  132  and motor  134  are enclosed as an assembly in the same housing and can be installed as a single assembly. In addition, housing  136  reduces the noise generated by blower assembly  114  during operation of motor  134  and blower  132 . Also, housing  136  includes one or more condensate drains  135  to allow condensation to be removed from the interior of housing  136 . 
     Also, in the exemplary embodiment, housing  136  has a height, width, and length that define a volume of housing  136 . Housing  136  is compact, i.e., has a volume that is less than at least some known systems, and is sized to simplify installation of blower assembly  114 . For example, in some embodiments, housing  136  has a height in a range of about 4 inches (in.) to about 18 in., a width in a range of about 6 in. to about 18 in., and a length in a range of about 6 in. to about 24 in. In the exemplary embodiment, housing  136  has a height of approximately 9 in., a width of approximately 14 in., and a length of approximately 9.5 in. In alternative embodiments, housing  136  is any size that enables blower assembly  114  to operate as described herein. 
     Moreover, in the exemplary embodiment, first portion  144  includes a bottom  150  and a first wall  152  extending upward from bottom  150  in reference to the orientation shown in  FIGS. 2 and 3 . Second portion  146  includes a top  154  and a second wall  156  extending downward from top  154  in reference to the orientation shown in  FIG. 2 . First wall  152  and second wall  156  extend between top  154  and bottom  150  when first portion  144  is coupled to second portion  146  such that bottom  150 , first wall  152 , top  154 , and second wall  156  collectively define cavity  148  when first portion  144  is coupled to second portion  146 . First portion  144  is a single piece, i.e., bottom  150  and first wall  152  are integrally formed and permanently joined together. Also, second portion  146  is a single piece, i.e., top  154  and second wall  156  are integrally formed and permanently joined together. Accordingly, housing  136  has a two-piece construction. Each of first portion  144  and second portion  146  form roughly half, e.g., an upper half and a lower half, of housing  136 . In alternative embodiments, housing  136  includes any portions  144 ,  146  that enable housing  136  to function as described herein. For example, in some embodiments, one of first portion  144  or second portion  146  defines more than half of housing  136  and the other defines less than half of housing  136 . 
     Moreover, in the exemplary embodiment, at least one of first portion  144  and second portion  146  defines an outlet  158  for airflow  118  to exit cavity  148 . In the exemplary embodiment, outlet  158  is defined by second portion  146  and extends upward from cavity  148 , in reference to the orientation shown in  FIG. 2 , to allow airflow  118  to flow to exhaust duct  116  (shown in  FIG. 1 ) positioned above blower assembly  114 . In some embodiments, outlet  158  includes a condensate trap to collect condensation as airflow flows through outlet  158  and into exhaust duct  116 . Outlet  158  may be coupled to exhaust duct  116  by a clamp  159  and/or other fastening devices. In alternative embodiments, blower assembly  114  includes any outlet  158  that enables blower assembly  114  to operate as described herein. 
       FIG. 4  is a top view of blower assembly  114  with first portion  144  (shown in  FIG. 2 ) removed. At least one of first portion  144  and second portion  146  includes a divider  160  separating motor  134  and blower  132  when blower  132  and motor  134  are positioned within cavity  148 . Accordingly, divider  160  separates cavity  148  into a motor cavity portion and a blower cavity portion. Housing  136  is sized and shaped to receive motor  134  and blower  132  within the respective cavity portion. Divider  160  is sealed to maintain separate airflows for blower  132  and motor  134 . 
     In the exemplary embodiment, divider  160  is defined by first portion  144  and second portion  146  (shown in  FIG. 2 ). Specifically, divider  160  has a lower portion integrally formed with first wall  152  and an upper portion integrally formed with second wall  156  (shown in  FIG. 2 ). Divider  160  extends between bottom  150  and top  154  (shown in  FIG. 2 ) and across a width of cavity  148  when first portion  144  is coupled to second portion  146 . Divider  160  defines an opening  162  for shaft  138  to extend through. A shaft seal  176  is disposed at least partially within opening  162  and extends around shaft  138  to seal opening  162 . In the exemplary embodiment, shaft seal  176  extends around the entire circumference of shaft  138  and between shaft  138  and first portion  144  and second portion  146 . Blower assembly  114  may include one or more bearings (not shown) to rotatably support shaft  138 . Accordingly, shaft  138  is able to extend between and drivingly couple motor  134  to blower  132  when motor  134  and blower  132  are positioned on opposite sides of divider  160 . In alternative embodiments, housing  136  includes any divider  160  that enables blower assembly  114  to operate as described herein. In some embodiments, divider  160  is omitted. 
     Also, in the exemplary embodiment, blower assembly  114  includes a controller compartment  164  defined by housing  136 . A vacuum switch  166  is positioned within controller compartment  164  and is configured to control motor  134  and to provide a safety circuit. Controller compartment  164  may include a removable or positionable cover to provide access to vacuum switch  166  and other components within controller compartment  164 . Vacuum switch  166  may be included in the control system for gas-burning appliance  100  (shown in  FIG. 1 ) or may be a standalone system. In alternative embodiments, blower assembly  114  includes any controller that enables blower assembly  114  to operate as described herein. 
     Moreover, in the exemplary embodiment, blower assembly  114  includes a cooling system  168  configured to draw cooling airflow  169  through housing  136 . Housing  136  defines an intake  170  and an exhaust  172 . A fan  174  is positioned in cavity  148  of housing  136  and is configured to generate cooling airflow  169  from intake  170  to exhaust  172 . Fan  174  is coupled to motor  134  and rotated when the shaft of motor  134  rotates. In alternative embodiments, blower assembly  114  includes any cooling system  168  that enables blower assembly  114  to operate as described herein. For example, in some embodiments, cooling system  168  includes a heat sink, a heat exchanger, and/or any other suitable cooling feature. 
       FIG. 5  is an enlarged sectional view of an inlet sleeve  178  of blower assembly  114  (shown in  FIGS. 2-4 ).  FIG. 6  is an enlarged sectional assembly view of a portion of a seal  186  of blower assembly  114  (shown in  FIGS. 2-4 ). In the exemplary embodiment, inlet sleeve  178  is coupled between wall  152  of first portion  144  and wall  156  of second portion  146  of housing  136 . Inlet sleeve  178  extends into cavity  148  adjacent blower  132  (shown in  FIGS. 2 and 3 ) to allow airflow  118  to enter cavity  148  (shown in  FIGS. 3 and 4 ). 
     In addition, in the exemplary embodiment, inlet sleeve  178  is configured to couple to gas-burning appliance  100  (shown in  FIG. 1 ) and receive airflow  118  from vent duct  112  of gas-burning appliance  100 . For example, inlet sleeve  178  extends on an exterior of housing  136  and is sized and shaped to receive vent duct  112  therein. In some embodiments, a clamp  180  or other fastener is used to couple vent duct  112  to inlet sleeve  178 . Inlet sleeve  178  may include a groove and lip configured to receive and retain clamp  180  in position. In some embodiments, a gasket or rubber sleeve  182  is positioned between inlet sleeve and vent duct  112 . In further embodiments, inlet sleeve  178  includes one or more features to facilitate engagement of inlet sleeve  178  and vent duct  112  such as grooves or slots  184  which allow for compression of inlet sleeve  178 . In alternative embodiments, inlet sleeve  178  is coupled to vent duct  112  in any manner that enables blower assembly  114  to operate as described herein. 
     Also, in the exemplary embodiment, inlet sleeve  178  is a separate piece from first portion  144  and second portion  146  (shown in  FIG. 2 ). In alternative embodiments, blower assembly  114  includes any inlet sleeve  178  that enables blower assembly  114  to operate as described herein. For example, in some embodiments, inlet sleeve  178  is integrally formed with at least one of first portion  144  and second portion  146 . In further embodiments, portions of inlet sleeve  178  are formed on each of first portion  144  and second portion  146  and coupled together when first portion  144  and second portion  146  are coupled together. 
     In addition, in the exemplary embodiment, blower assembly  114  includes a seal  186  extending around at least a portion of inlet sleeve  178  and between inlet sleeve  178  and at least one of first portion  144  and second portion  146 . In the exemplary embodiment, inlet sleeve  178  is a separate piece from both first portion  144  and second portion  146  and seal  186  extends around the entire perimeter of inlet sleeve  178  and between inlet sleeve  178  and both first portion  144  and second portion  146 . In alternative embodiments, inlet sleeve  178  is integrally formed with first portion  144  or second portion  146  and seal  186  does not extend between inlet sleeve  178  and the respective portion. 
     Moreover, in the exemplary embodiment, inlet sleeve  178  includes a tubular body  188  and a collar  190  extending around and radially outward from tubular body  188 . Tubular body  188  defines a passageway  192  for airflow  118  to flow through inlet sleeve  178 . Collar  190  defines a channel  194  to receive walls  152 ,  156  of first portion  144  and second portion  146  and couple inlet sleeve  178  to walls  152 ,  156  when inlet sleeve  178  is positioned between first portion  144  and second portion  146 . 
     As shown in  FIG. 6 , seal  186  is an overmold and is configured to be disposed at least partially within channel  194  (shown in  FIG. 5 ). Seal  186  is substantially U-shaped and includes lips  196  that extend over an edge of collar  190 . Seal  186  is shaped to receive walls  152 ,  156  and may include one or more notches or other features that correspond to the shapes of walls  152 ,  156 . In addition, seal  186  has a width that is slightly less than the thickness of walls  152 ,  156  to provide an interference fit when walls  152 ,  156  are received within channel  194 . 
     Also, in the exemplary embodiment, seal  186  is an elastic material such as rubber. In alternative embodiments, blower assembly  114  includes any seal  186  that enables blower assembly  114  to operate as described herein. 
     In some embodiments, inlet sleeve  178  includes an optional pressure tap  198  to allow regulation of the pressure of fluid flowing through inlet sleeve  178 . Pressure tap  198  may be coupled to and extend through tubular body  188 . In further embodiments, blower assembly  114  may include any suitable valve and/or pressure regulator. In alternative embodiments, pressure tap  198  is omitted. 
     Referring to  FIGS. 1-5 , a method of assembling blower assembly  114  for gas-burning appliance  100  includes coupling first portion  144  to second portion  146  such that first portion  144  and second portion  146  define cavity  148  therebetween to receive motor  134  and blower  132 . Motor  134  and blower  132  are positioned within cavity  148  and coupled together by shaft  138  extending through opening  162  in divider  160 . Motor  134  and blower  132  are completely enclosed within housing  136  when first portion  144  and second portion  146  are coupled together. For example, first portion  144  and second portion  146  are coupled together by positioning opposing edges of first wall  152  and second wall  156  in contact with each other and securing first portion  144  and second portion  146  together. In the exemplary embodiment, first portion  144  and second portion  146  are fastened together using fasteners positioned in openings in first portion  144  and second portion  146 . In alternative embodiments, first portion  144  and second portion  146  are coupled together in any manner that enables housing  136  to function as described herein. 
     The method also includes coupling inlet sleeve  178  between first portion  144  and second portion  146  and positioning seal  186  at least partially around inlet sleeve  178  and at least partially between inlet sleeve  178  and at least one of first portion  144  and second portion  146 . For example, inlet sleeve  178  is positioned such that first wall  152  and second wall  156  are received in channel  194  of inlet sleeve  178 . Seal  186  is positioned within channel  194  to contact and, thereby, seal inlet sleeve  178  and housing  136 . First portion  144  and second portion  146  are coupled together with inlet sleeve  178  positioned therebetween. 
     In some embodiments, the method further includes coupling inlet sleeve  178  to vent duct  112  and coupling outlet  158  to exhaust duct  116 . Accordingly, blower assembly  114  is arranged to induce airflow  118  through gas-burning appliance  100  and exhaust airflow  118  through exhaust duct  116 . In the exemplary embodiment, blower assembly  114  is positioned on top of tank  102  and housing  136  is mounted to enclosure  122  above tank  102 . 
     The methods and systems described herein provide several advantages and improvements over prior methods and systems. For example, the technical effect may include at least one of: (a) decreasing the cost to assemble the blower assembly; (b) reducing the noise generated during operation of the blower assembly; (c) ensuring proper ventilation of combustion gasses from the gas-burning appliance; (d) improving efficiency of combustion and heat transfer in the gas-burning appliance; and (e) simplifying selection, installation, and configuration of gas-burning appliances by providing a modular, cost effective blower assembly for gas-burning appliances. 
     The systems and methods described herein are not limited to the specific embodiments described herein, but rather, components of the systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. 
     This written description uses examples to provide details on the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.