Abstract:
A heater assembly used in connection with a diesel emissions fluid tank in a vehicle, the heater assembly including a first heater connectable to an alternating current power supply; a second heater connectable to a direct current power supply within the vehicle; wherein the first heater is adapted to operate at a higher power than the second heater; wherein the first heater is closer to the tank than the second heater; a temperature sensor in sensing communication with the tank and adapted to provide a tank temperature; a control circuit connected to the second heater and the vehicle power supply, wherein the temperature sensor communicates the tank temperature to the control circuit, wherein the control circuit selectively activates the second heater to obtain a desired tank temperature.

Description:
TECHNICAL FIELD 
       [0001]    In general, the present invention relates to a heater assembly used in connection with diesel exhaust fluid in a tank. In particular, the present invention relates to a multiple mode heater assembly having a high power heater adjacent to the tank and a lower power heater located outward of the high power heater to separately apply higher and lower power heat to the tank to prevent freezing. 
       BACKGROUND OF THE INVENTION 
       [0002]    Diesel emissions are an environmental concern that has limited application of diesel engines despite the fuel efficiency offered by these engines. To reduce harmful emissions, technologies that treat the exhaust gas downstream of the engine have been developed including selective catalytic reduction systems that inject a small quantity of diesel exhaust fluid (DEF) into the exhaust upstream of a catalyst where is vaporizes and decomposes to form ammonia and carbon dioxide. The ammonia (NH 3 ) converts nitrogen oxides (NOx) within the exhaust gas to harmless nitrogen (N 2 ) and water (H 2 O). It has been estimated that DEF consumption is approximately 2% of fuel consumption within a typical diesel engine. Consequently, significant amounts of DEF must be stored in a tank or reservoir within a vehicle for dosing in the exhaust system. One DEF that has gained wide acceptance through regulation is an Aqueous Urea Solution on (AUS). 
         [0003]    Aqueous Urea Solutions are effective in reducing nitrogen oxides (NOx) contained in the exhaust gas of an engine. One drawback, however, is the freezing temperature for Aqueous Urea Solution is about −11° C. (12° F.) placing it within the ambient temperature range of colder regions. To avoid freezing of the solution, it is known to use an electric resistance heater or heat exchanger using engine coolant to warm or thaw the Aqueous Urea Solution. The present invention improves upon these techniques. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention generally includes two heaters that may be fastened to an external surface of a diesel exhaust fluid tank. The first heater is located closest to the tank and is a higher power heater. The second heater is spaced from the tank at least by the first heater. The second heater is a lower power heater. 
         [0005]    According to additional concepts of the present invention, the first heater may be activated by connecting it to an external power source causing the heater to run continuously until disconnected from the power source. A thermostat may be provided to measure the first heater surface temperature or temperature of the heated fluid, and operate the heater in a desired temperature range. 
         [0006]    According to additional concepts of the present invention, the lower power heater may be powered by the vehicle. This heater may by connected to a control module that communicates with a temperature sensor in the Aqueous Urea Solution and selectively activates the heater to regulate the Aqueous Urea Solution fluid temperature by cycling the heater on and off. The control circuit may include an override control that disables the heater upon detecting a temperature that would potentially degrade the fluid or cause system damage. 
         [0007]    According to further concepts of the present invention, the first heater may directly contact the tank surface. 
         [0008]    According to further concepts of the invention, the second heater may be bonded to the first heater. 
         [0009]    According to still further concepts of the present invention, the heater assembly may be attached to a lower portion of the diesel engine fluid tank. The heater assembly may be attached to the bottom surface of the diesel engine fluid tank. 
         [0010]    According to another concept of the present invention, thermal insulation may be used to reduce heat loss and improve heat flow to the fluid in the tank. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic sectioned side elevational view of a diesel exhaust fluid tank having a multi-mode heater assembly according to the concepts of the present invention attached to the tank. 
           [0012]      FIG. 2  is a schematic view of a multi-mode heater assembly system used in connection with a vehicle according to the concepts of the present invention. 
           [0013]      FIG. 3  is an exploded view of a multi-mode heater assembly according to the concepts of the present invention showing details of the first and second heaters, a support plate, and insulation. 
           [0014]      FIG. 4  is a perspective view of a multi-mode heater assembly showing details of a stacked heater configuration with support plate and insulation attached. 
           [0015]      FIG. 5  is a fragmented cross sectional view as might be seen along line  5 - 5  in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    A multimode heater assembly according to the concepts of the present invention is generally indicated by the number  10  in the accompanying drawings. Heater assembly  10  is used in connection with a tank  15  for holding a diesel emissions fluid (DEF). Tank  15  is generally a container capable of holding DEF for use in a vehicle V. Tank  15  has an outer surface that includes a base  16 . The DEF may be an aqueous urea solution (AUS). To prevent the AUS from freezing, heater assembly  10  may be used in connection with tank  15  to maintain the DEF above its freezing temperature, for example, −11° C. for AUS. A heater assembly  10  generally includes a first heating element or first heater  11  and a second heating element or second heater  12 . The first heater  11  is a higher power heater relative to the second heater  12 . To that end, first heater  11  provides more intense heat to the DEF tank  15  than second heater  12 . For example, in a locomotive application, first heater may be a 1,500 watt heater adapted to operate with 660 volt AC three-phase power supply and second heater may be a 550 watt heater adapted to operate with a 74 volt DC power supply. It will be appreciated that the heater assembly  10  may be applied to other vehicles and adapted for use with other power supplies. Depending on the vehicle application, the power of each heater  11 ,  12  may be vary in accordance with the size of the tank and amount of fluid that needs to be heated. Additional heater assemblies with a common power may be laid adjacent to each other to provide more heat and/or distribute heat over a larger surface. Other considerations may be the average operating temperatures for the vehicle. 
         [0017]    As best shown in  FIG. 1 , first and second heaters  11 ,  12  may be supported by a support bracket generally indicated by the number  20 . In the example shown, support bracket  20  includes first and second brackets  21 ,  22  that encompass the sides of heaters  11 ,  12  and a lower support plate  23  that extends below the first and second heaters  11 ,  12 . 
         [0018]    Heaters  11 ,  12  are arranged in a stacked configuration with the first heater  11  located closest to the tank  15 . In the example shown, the first heater  11  is in contact with the base  16  of the tank  15 . In this configuration, the maximum amount of heat may be transferred from the first heater  11  to the base  16  of tank  15 . It will be appreciated, however, that other configurations may be used placing the first heater  11  in contact with various portions of the tank as desired. In addition, direct contact between the first heater  11  and the tank  15  is not necessary, but indirect heating may result in a lower rate of heat transfer than the configuration shown. 
         [0019]    Second heater  12  is generally spaced outward from the first heater  11  and, as shown in the depicted example, may be in direct contact with the first heater  11 . In this configuration, the first surface or upper surface  25  of first heater  11  contacts the tank  15  and the second or lower surface  26  of first heater  11  contacts a first or upper surface  27  of second heater  12 . The second or lower surface  28  of second heater  12  may be supported by support plate  23  as shown. 
         [0020]    First and second heaters  11 ,  12  may operate independently and may be powered by one or more power supplies. Each heater  11 ,  12  may have its own power supply. For example, first heater  11  may be powered by an alternating current (AC) voltage circuit  30 . Second heater  12  may be powered by a direct current (DC) voltage supply circuit  32 . In the example shown, the AC heating circuit  30  is external to the vehicle V such that the first heater  11  is connected to the AC heating circuit  30  by a connector  34  such as an electrical cord. To that end, the first heater  11  may be activated simply by plugging it into the AC voltage circuit  30 . The first heater  11  may be operated continuously until it is unplugged from the AC voltage circuit  30 . 
         [0021]    A thermostat  35  or other temperature sensor may be provided to measure the surface temperature of first heater  11  and set to operate the first heater  11  in a selected temperature range to prevent over heating of the diesel emissions fluid or damage to the heaters  11 ,  12  or tank  15 . To accommodate the thermostat  35 , a sensor receiver may be formed in support plate  23  shown as a notch in plate  23 . A similar notch may be formed in the insulation  50 , which is described in more detail below. By placing the first heater  11  directly in contact with the surface of tank  15  the maximum heat sink is utilized to pull heat away from heater  11  and reduce its temperature. The second heater  12  has less heat sink because it is spaced from the tank  15 . In the depicted example, second heater  12  is bonded to the lower surface  26  of first heater  11  and not directly to the tank  15 . Since it is expected that the second heater  12  would have a higher surface temperature, second heater  12  is provided with a lower heat density, i.e., the amount of heat over its surface area, to prevent over heating of the heater  12 . As graphically depicted, the second heater  12  may be connected to a DC voltage circuit  32  located within the vehicle V. 
         [0022]    In operation of the depicted system, it is expected that the first heater  11  will be used to thaw a tank  15  of frozen DEF using an external alternating current voltage circuit  30  applying maximum heat to the tank  15 . The second heater  12 , which would be connected to a mobile DC voltage circuit  32  such as one located within the vehicle V would operate as needed to prevent freezing of the DEF or provide thawing when an AC circuit is not readily available. 
         [0023]    A control module  40  may be connected to a temperature sensor  42  located within tank  15  that measures the temperature of the DEF. As shown, control module  40  may separate the second heater  12  and DC voltage circuit  32  to control application of the DC voltage to the second heater  12 . In this arrangement, the second heater  12  and DC voltage circuit  32  are each electrically connected to the control module  40 . The control module  40  selectively connects DC voltage circuit  32  to second heater  12  by control module  40  may be constant or delivered in a pulsatory or other programmed manner to perform thawing or obtain a selected temperature. For example, when control module  40  detects a temperature indicating a potential for freezing of the DEF, control module  40  activates second heater  12  by supplying power from the DC voltage circuit  32  to second heater  12 . When the temperature seen by temperature sensor  42  reaches an acceptable level, control module  40  may deactivate the second heater  12 . The control module  40  may be any circuit, programmable logic controller, or processor based controller capable of regulating operation of the heating element(s). 
         [0024]    As an alterative to the arrangement described above, with respect to first heater  11 , the control module  40  may be used in the same fashion to control application of heat to the first heater  11  by locating the control module  40  between the first heater  11  and the AC voltage circuit  30 . In contrast to the previous described example, rather than relying on plugging and unplugging the first heater  11  into the AC voltage circuit  30  to control activation of the first heater  11 , the control module would monitor the temperature of the fluid within the tank  15  to selectively activate or deactivate the first heater  11  by controlling the supply of current from the AC voltage source  30 . 
         [0025]    In terms of construction, first and second heaters  11 ,  12  may be resistance type heating elements or other heating elements known in the art. The first and second heaters  11 ,  12  may be thin pad heaters characterized as having at least one surface dimension that is greater than the thickness of the pad. In the example shown, the length and width surface dimensions are both greater than the thickness of heaters  11 ,  12 . With reference to  FIGS. 3-5 , first and second heaters  11 ,  12  may be constructed by attaching a resistance wire to a steel sheet. For example, a resistance wire may be attached and encapsulated in a silicone elastimer and attached to steel sheet to form a thin pad heater. Heaters  11 , 12  may be arranged to apply heat to the same area of tank  15 . For example, as shown, heaters  11 , 12  may be arranged in a stacked configuration so that they both apply heat to the same area of tank  15 . In the example shown, the heaters  11 , 12  are stacked beneath a lower surface or base  16  of tank  15 . In the stacked arrangement shown, the first heater  11  and second heater  12  may be bonded together. Bonding of the heaters  11 , 12  may be achieved by any suitable fastener or adhesive. In the depicted embodiment, heaters  11 ,  12  are stacked and bonded with mechanical fasteners, for example, bolts or screws (not shown), that sandwich the heaters  11 , 12  between a support plate  23  and tank  15 . As best shown in  FIGS. 4 and 5 , to accommodate such fasteners, receivers, generally indicated by the number  45 , may be formed in the heaters  11 , 12  (receivers  45 A, 45 B) and support plate  23  (receivers  45 C) to allow the fasteners (not shown) to pass therethrough and attach heater assembly  10  to tank  15 . It will be appreciated that support plate  23  may be constructed of any material that is suitable for supporting the heaters  11 , 12 . 
         [0026]    Placement of the heater assembly  10  on the base  16  of tank  15  is believed to provide greater efficiency by taking advantage of the natural convection to distribute heat upward to the tank  15 . While potentially less efficient, other configurations may be used within the concepts of the present invention. To reduce heat loss and improve the flow of heat from heaters  11 ,  12  to tank  15 , insulation  50  may be provided around the exterior of heater assembly  10 . For example an insulation pad  50  may be supported on bracket  20  below heaters  11 , 12  to insulate them from the ambient air. In the depicted example, insulation  50  is a closed cell foam insulation sheet material. In addition to or as an alternative, support plate  23  may be constructed from an material that has some insulating properties or wrapped or coated in heat shielding material to further reduce heat loss. In the example shown, insulation pad  50  is supported outward of support plate  23  to insulate heaters and shield users from the heat generated by heaters  11 , 12 . As best shown in  FIGS. 3 and 4  to facilitate attachment, insulation pad  50  may have receivers  45 D corresponding to the receivers  45 A, 45 B, 45 C respectively in heaters  11 , 12  and support plate  23  so that the heater assembly  10 , support plate  23 , and insulation  50  may be fastened to tank  15  with the same fasteners. 
         [0027]    Overall, a heater assembly used in connection with a diesel exhaust fluid tank has been described and provides a new and useful addition to the art. It will be appreciated that various modifications and substitutions may be made to the described embodiments without departing from the scope of the present invention. Therefore, for an appreciation of the scope of the invention, reference is made to the following claims.