Abstract:
A vehicle subsystem according to an exemplary aspect of the present discourse includes, among other things, a wall structure and a thermal resistance feature internal to the wall structure and configured to inhibit heat loss through the wall structure.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to a vehicle subsystem. A wall structure of the vehicle subsystem includes a thermal resistance feature configured to inhibit heat loss through the wall structure. 
       BACKGROUND 
       [0002]    Modern day vehicles include numerous components that attain relatively high temperatures during the course of vehicle operation. The engine and the transaxle are two examples of such vehicle components. At elevated temperatures of the engine and transaxle, the losses caused by friction are relatively low resulting in reduced fuel consumption. However, the engine and transaxle lose heat to their surroundings when the vehicle is turned off. Over time, these components slowly cool down and eventually reach equilibrium with the ambient temperature. When the vehicle is subsequently turned on in this cooled down state, the losses due to friction are relatively high, thereby increasing fuel consumption compared to the elevated temperature state. 
         [0003]    After the cold start, the engine coolant first needs to warm up before it can provide heat to the vehicle cabin, thereby causing occupant discomfort in winter. Moreover, to satisfy emission requirements for a hybrid electric vehicle (HEV), a cold engine requires the vehicle subsystem controller to keep the engine running regardless of propulsion needs until a prescribed engine temperature is reached. This means the HEV system functionality is not utilized during this time and possible fuel economy gains are not achieved. 
       SUMMARY 
       [0004]    A vehicle subsystem according to an exemplary aspect of the present discourse includes, among other things, a wall structure and a thermal resistance feature internal to the wall structure and configured to inhibit heat loss through the wall structure. 
         [0005]    In a further non-limiting embodiment of the foregoing vehicle subsystem, the wall structure is part of an engine. 
         [0006]    In a further non-limiting embodiment of either of the foregoing vehicle subsystems, the wall structure is part of a transaxle. 
         [0007]    In a further non-limiting embodiment of any of the foregoing vehicle subsystems, the thermal resistance feature includes an air pocket formed inside the wall structure. 
         [0008]    In a further non-limiting embodiment of any of the foregoing vehicle subsystems, the air pocket has been evacuated of air. 
         [0009]    In a further non-limiting embodiment of any of the foregoing vehicle subsystems, a rib extends across the air pocket between at least two solid surfaces of the wall structure. 
         [0010]    In a further non-limiting embodiment of any of the foregoing vehicle subsystems, the thermal resistance feature includes insulation that is sandwiched between a first layer and a second layer of the wall structure. 
         [0011]    In a further non-limiting embodiment of any of the foregoing vehicle subsystems, at least one fastener extends through the first layer, the insulation and the second layer. 
         [0012]    In a further non-limiting embodiment of any of the foregoing vehicle subsystems, the wall structure includes an external wall, an internal wall, a top wall and a bottom wall. 
         [0013]    In a further non-limiting embodiment of any of the foregoing vehicle subsystems, the thermal resistance feature is disposed between the external wall and the internal wall. 
         [0014]    In a further non-limiting embodiment of any of the foregoing vehicle subsystems, the wall structure includes at least one solid section adjacent to the thermal resistance feature. 
         [0015]    A vehicle according to another exemplary aspect of the present disclosure includes, among other things, an engine, a transaxle selectively driven by the engine and at least one of the engine and the trans axle including a wall structure having a thermal resistance feature built into the wall structure and configured to inhibit heat loss out of the engine or the transaxle. 
         [0016]    In a further non-limiting embodiment of the foregoing vehicle, the thermal resistance feature includes an air pocket formed inside the wall structure. 
         [0017]    In a further non-limiting embodiment of either of the foregoing vehicles, the air pocket extends between an external wall and an internal wall of the wall structure. 
         [0018]    In a further non-limiting embodiment of any of the foregoing vehicles, a rib extends across the air pocket between a first solid surface and a second solid surface. 
         [0019]    In a further non-limiting embodiment of any of the foregoing vehicles, the first solid surface and the second solid surface are internal surfaces of the wall structure. 
         [0020]    In a further non-limiting embodiment of any of the foregoing vehicles, the air pocket has been evacuated of air. 
         [0021]    In a further non-limiting embodiment of any of the foregoing vehicles, the thermal resistance feature includes insulation that is sandwiched between a first layer and a second layer of the wall structure. 
         [0022]    In a further non-limiting embodiment of any of the foregoing vehicles, at least one fastener extends through the first layer, the insulation and the second layer. 
         [0023]    In a further non-limiting embodiment of any of the foregoing vehicles, an electric machine is configured to selectively drive the transaxle. 
         [0024]    The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
         [0025]    The various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  schematically illustrates a powertrain of a vehicle. 
           [0027]      FIG. 2  illustrates a vehicle subsystem. 
           [0028]      FIG. 3  illustrates a wall structure of a vehicle subsystem according to a first embodiment of this disclosure. 
           [0029]      FIG. 4  illustrates a wall structure according to a second embodiment of this disclosure. 
           [0030]      FIG. 5  illustrates wall structure according to another embodiment of this disclosure. 
           [0031]      FIG. 6  illustrates yet another exemplary wall structure. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    This disclosure details a vehicle subsystem. The vehicle subsystem includes a wall structure and a thermal resistance feature inside the wall structure. The thermal resistance feature is configured to inhibit heat loss through the wall structure. In some embodiments, the wall structure is part of a vehicle engine. In other embodiments, the wall structure is part of a vehicle transaxle. These and other features are discussed in greater detail in the following paragraphs of this detailed description. 
         [0033]      FIG. 1  schematically illustrates a vehicle  10 . This disclosure is applicable to any type of vehicle. For example, the vehicle  10  could be a conventional vehicle that is powered by an internal combustion engine, or could be configured as a hybrid electric vehicle that is powered by one or more electric machines in addition to the internal combustion engine. 
         [0034]    The exemplary vehicle  10  includes a powertrain  12 . The powertrain  12  may include a propulsion device  14  and a transaxle  15  that is selectively driven by the propulsion device  14 . The propulsion device  14  may be employed as an available drive source for the vehicle  10 . The propulsion device  14  may include an internal combustion engine if the vehicle  10  is configured as a conventional vehicle. Alternatively, the propulsion device  14  could include an internal combustion engine and an electric machine (i.e., an electric motor, a generator or a combined motor/generator) if the vehicle  10  is configured as an electrified vehicle. 
         [0035]    The transaxle  15  includes a transmission  16 . The transmission  16 , which is shown schematically, may include a gearbox having multiple gear sets (not shown) that are selectively operated using different gear ratios by selective engagement of friction elements such as clutches and brakes (not shown) to establish the desired multiple discrete or step drive ratios. The friction elements are controllable through a shift schedule that connects and disconnects certain elements of the gear sets to control the ratio between a transmission input shaft  19  and a transmission output shaft  20  of the transaxle  15 . The transmission  16  may alternatively be controlled to achieve an infinite number of ratios. These ratios can be achieved through mechanical reconfiguration as in a continuously variable transmission (CVT) or by electrical coordinate of the speeds of electric machines as in an electrically continuously variable transmission (eCVT). The transmission  16  may be automatically shifted from one ratio to another based on various vehicle and ambient operating conditions by an associated control module. The transmission  16  then provides powertrain output torque to the transmission output shaft  20 . 
         [0036]    The transmission output shaft  20  may optionally be connected to a differential  22  of the transaxle  15 . The differential  22  drives a pair of wheels  24  via respective axles  26  that are connected to the differential  22  to propel the vehicle  10 . The transaxle  15  may be configured as either a front wheel drive or rear wheel drive platform. 
         [0037]    One or more energy sources  18  may supply power to the propulsion device(s)  14 . The energy source  18  may include a fuel system if the propulsion device  14  is an engine and/or a high voltage battery pack if the propulsion device  14  is an electric machine. For example, an engine is configured to consume fuel (i.e., gasoline, diesel, etc.) to produce a motor output, whereas the high voltage battery pack is configured to output and receive electrical energy that is consumed by the electric machine to produce a motor output. In one non-limiting embodiment, the vehicle  10  may include both a fuel system and the high voltage battery pack as available energy sources  18  where the vehicle  10  is configured as a hybrid electric vehicle. 
         [0038]      FIG. 2  is a highly schematic depiction of a vehicle subsystem  54  that can be incorporated into a vehicle. For example, the vehicle subsystem  54  could be employed within the vehicle  10  of  FIG. 1 . In one non-limiting embodiment, the vehicle subsystem  54  is a heat generating vehicle subsystem, such as an engine or a transaxle. The vehicle subsystem  54  may include one or more components  56  (two shown in this non-limiting embodiment) that generate heat H during operation of the vehicle subsystem  54 . The components  56  may include any part that creates friction during operation of the vehicle subsystem  54 , including but not limited to, cylinders, mating parts, gears, clutches, brakes, etc. 
         [0039]    The vehicle subsystem  54  includes a wall structure  58  that surrounds the components  56 . The components  56  may be in direct contact with the wall structure  58 , or could be spaced away from the wall structure  58  in an indirect thermal connection to the wall structure  58 . Heat H generated by the components  56  is transferred to the wall structure  58  through these direct or indirect pathways and is subsequently lost to the ambient surroundings AS. The wall structure  58  may establish an interior I for housing the components  56 . The interior I may contain a gaseous or a liquid medium or any combination of mediums. 
         [0040]    The wall structure  58  is configured to retain the heat H generated by the vehicle subsystem  54  within the interior I. In one embodiment, one or more thermal resistance features  68  may be formed inside the wall structure  58  to inhibit the loss of the heat H from the interior I to ambient surroundings AS. For example, each thermal resistance feature  68  acts as a suitable thermal barrier so the vehicle subsystem  54  losses heat H to the ambient surroundings AS at a slower rate compared to standard wall structures Inhibiting heat loss in this manner allows the vehicle subsystem  54  to begin operating the components  56  at a temperature greater than the ambient temperature of the ambient surroundings AS after the heat generating components  56  have been inactive for a long duration of time. With this inhibiting heat loss feature, the components  56  warm up at a rate faster than standard wall structures. Therefore, improved fuel economy may be achieved because friction losses are lower at the higher temperatures. This also means heat may be provided to the vehicle cabin much sooner and satisfy key thermal comfort metrics. Various wall structures having built-in thermal resistance features that inhibit heat loss are described below with reference to  FIGS. 3-6 . 
         [0041]      FIG. 3  illustrates an exemplary wall structure  58  adapted to inhibit heat loss out of a vehicle subsystem. The wall structure  58  may include an external wall  60 , an internal wall  62 , a top wall  64 , and a bottom wall  66 . The exterior wall  60  faces toward the ambient surroundings AS of the vehicle subsystem  54 , and the internal wall  62  faces toward the interior I of the vehicle subsystem  54  (see also  FIG. 2 ). 
         [0042]    A thermal resistance feature  68  may be built into the wall structure  58 . For example, in one non-limiting embodiment, the thermal resistance feature  68  is disposed inside the wall structure  58  between the external wall  60  and the internal wall  62 . The thermal resistance feature  68  may also be disposed between the top wall  64  and the bottom wall  66 . 
         [0043]    In one embodiment, the thermal resistance feature  68  includes an air pocket  70  disposed inside the wall structure  58 . The air pocket  70  splits the wall structure  58  into a multi-layered wall with an air gap extending between the layers. The air pocket  70  may extend between a first surface  90  of the external wall  60  and a second surface  92  of the internal wall  62 . In one embodiment, both the first surface  90  and the second surface  92  are solid, internal surfaces of the wall structure  58 . 
         [0044]    The air pocket  70  is a relatively poor conductor of heat and thus inhibits heat loss through the wall structure  58  by increasing the thermal resistance from the internal wall  62  toward the external wall  60 . It should be understood that the wall structure  58  could include one or more air pockets  70  periodically disposed throughout the wall structure  58 . In other words, the wall structure  58  may include solid sections  96  in addition to the air pocket  70 . 
         [0045]    The wall structure  58  may be made using a metallic material. In one embodiment, the wall structure  58  is made of aluminum. In another embodiment, the wall structure  58  is made of iron. Other high strength and high rigidity materials are also contemplated as within the scope of this disclosure. 
         [0046]      FIG. 4  illustrates another exemplary wall structure  158 . In this disclosure, like reference numbers designate like elements where appropriate and reference numerals with the addition of  100  or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding original elements. 
         [0047]    In this exemplary embodiment, the wall structure  158  is similar to the wall structure  58  of  FIG. 3  and includes a thermal resistance feature  168  configured as a vacuum pocket  170 . In this embodiment, the vacuum pocket  170  has been evacuated of air. Evacuating the air within the vacuum pocket  170  substantially eliminates thermal conduction thus leaving thermal radiation as the only heat transfer mechanism that can occur across the vacuum pocket  170 . The vacuum pocket  170  may therefore further reduce heat loss that can occur through the wall structure  158  from the internal wall  162  toward the external wall  160 . 
         [0048]      FIG. 5  illustrates yet another wall structure  258 . The wall structure  258  is similar to the wall structure  58  of  FIG. 3  but includes a rib  72  that extends across an air pocket  270  formed inside the wall structure  258 . In one embodiment, the rib  72  extends between a first solid surface  290  and a second solid surface  292  that surround the air pocket  270 . The rib  72  increases the strength and rigidity of the wall structure  258 . Although a single rib  72  is shown, multiple ribs  72  could extend across the air pocket  270 . In one non-limiting embodiment, the rib  72  is made of a non-conductive material. In another non-limiting embodiment, the rib  72  is made from the same material as the wall structure  258 . 
         [0049]    Another wall structure  358  is illustrated in  FIG. 6 . In this embodiment, the wall structure  358  includes a first layer  76 , a second layer  78  and a thermal resistance feature  368  between the first layer  76  and the second layer  78 . In one embodiment, the thermal resistance feature  368  includes insulation  80  sandwiched between the first layer  76  and the second layer  78 . The insulation  80  may be held in place using one or more fasteners  82  that extend through each of the first layer  76 , the insulation  80  and the second layer  78 . The insulation  80  is adapted to inhibit heat loss through the wall structure  358 , such as in a direction extending from the second layer  78  toward the first layer  76  (i.e., toward surrounding atmosphere). 
         [0050]    The various embodiments of this disclosure incorporate thermal resistance features inside the wall structures of heat generating vehicle subsystems. The thermal resistance features exhibit increased thermal resistance for reducing heat loss out of the wall structures. Reducing heat loss in this manner allows vehicle subsystem operation to begin at a higher than ambient temperatures to provide improved fuel economy. 
         [0051]    Although the different non-limiting embodiments are illustrated as having specific components or steps, the embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments. 
         [0052]    It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should be understood that although a particular component arrangement is disclosed and illustrated in these exemplary embodiments, other arrangements could also benefit from the teachings of this disclosure. 
         [0053]    The foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.