Abstract:
An axle includes a differential, a cover, and a heat absorber. The differential has a ring gear disposed within a housing. The ring gear is configured to pump a lubricating fluid. The cover is attached to the housing. The heat absorber is attached to the cover within a pump path of the ring gear. The heat absorber has a phase-change material disposed within the heat absorber configured to absorb heat from the lubricating fluid. A method to control fluid temperature in a vehicle axle is also included.

Description:
TECHNICAL FIELD 
     The present disclosure relates to vehicle axles. More particularly, the disclosure relates to an axle assembly utilizing a heat absorber with a phase-change material. 
     BACKGROUND 
     Vehicle driveline components such as gears, bearings, and other components require lubrication. Various characteristics of the lubricating fluid, such as viscosity, temperature, and fluid levels may affect durability, drivability, and fuel economy. Due to parasitic losses, some energy is converted to heat rather than being transmitted to downstream components. In addition to providing lubrication to minimize the parasitic losses, the fluid transfers the resulting heat away from the gears and bearings. The lubricating fluid may overheat during various operations of the vehicle, such as towing a trailer. Overheating the lubricating fluid may cause damage to the gears, bearings, and other components of the driveline. 
     SUMMARY 
     An axle for a vehicle includes housing, and a heat absorber. The housing contains a lubricating fluid. The heat absorber is attached to an interior of the housing and contains a phase-change material. The heat absorber is configured to absorb heat from the lubricating fluid by inducing a phase-change of the phase-change material. 
     An axle includes a differential, a cover, and a heat absorber. The differential has a ring gear disposed within a housing. The ring gear configured to pump a lubricating fluid. The cover is attached to the housing. The heat absorber is attached to the cover within a pump path of the ring gear. The heat absorber has a phase-change material disposed within the heat absorber configured to absorb heat from the lubricating fluid. 
     A method to control fluid temperature in a vehicle axle includes attaching a heat absorber to axle housing in a fluid path of a lubricating fluid. The method further includes filling a plurality of protrusions defined on the heat absorber with a phase-change material and pumping fluid across the heat absorber. The method also includes absorbing heat from the fluid by changing a phase of the phase-change material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a vehicle; 
         FIG. 2  is an inner perspective view of an axle housing for a vehicle; and 
         FIG. 3  is a cross-sectional view of an axle housing for a vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
     Referring to  FIG. 1 , a schematic of a vehicle  10  is shown. The vehicle  10  includes an engine/transmission  12 , and a rear axle assembly  14  which includes a ring gear  16  and a housing  40 . The engine/transmission  12  provides torque to drive ring gear  16 . The rear axle assembly  14  transfers torque from the engine/transmission  12  through left and right axle shafts  15  to the rear vehicle wheels  13  while allowing slight differences in wheel speed as the vehicle turns corners. As ring gear  16  spins, it pumps lubricating fluid within the housing  40  to distribute the fluid to various gears and bearings. Pumping the lubricating fluid exerts some parasitic torque on ring gear  16  which decreases the torque transmitted to the wheels  13 . This is known as a spin loss because the magnitude is strongly influenced by rotational speed as opposed to transmitted torque. The magnitude is also influenced by the quantity of fluid and the fluid viscosity. It is important to maintain an appropriate level of fluid at an appropriate temperature. When the temperature of the lubricating fluid is cold, the viscosity is high increasing the magnitude of the ring gear spin loss. If the temperature gets too high, the fluid becomes ineffective at removing heat from gears and bearings, causing those components to lose efficiency and wear prematurely. If the temperature increases too much, for example above 145 degrees Celsius, chemical reactions can occur which degrade the effectiveness of the fluid as a lubricant. Increasing the quantity of fluid increases the ring gear parasitic loss and also increases the time required for the fluid temperature to reach a normal operating temperature. Both of these effects decrease fuel economy. However, if the quantity of fluid is too low, the temperature may increase too much during demanding operations such as towing a trailer up a hill. 
       FIG. 2  is a cutaway perspective view of a first embodiment of the axle assembly  14  from behind and to the left (driver&#39;s side). The housing  40  includes a cover  20  which may be mechanically fastened at the rear of the housing  40  by bolts, for example. When the vehicle is moving forward, ring gear  16  pumps the lubricating fluid across the cover  20 . Ring gear  16  may be centered vertically on a central axis  22  that passes through the cover  20 . The housing and cover define a sump. Ring gear  16  distributes fluid from the sump to components such as gears and bearing that need lubrication. Gravity causes fluid within the housing to drain to the sump. The level of the fluid when the vehicle is stationary and all fluid has drained to the sump is called the static fluid level  32 . 
     A heat absorber composed of a non-insulating material is fixed to the interior of the housing. In the embodiment of  FIG. 2 , the heat absorber is located in the sump below the static fluid level. The heat absorber  26  may include a plurality of plates  25  to increase the surface area for convective heat transfer between the lubricating fluid and the heat absorber. In at least one other embodiment, the heat absorber  26  may have a rectangular box shape, an arcuate shape, or other shape. The heat absorber defines an internal cavity which contains a phase-change material  28 . The phase-change material  28  may be material capable of changing phase upon reaching a temperature threshold. The phase-change material  28  may include but is not limited to any type of salts, inorganic liquids, or organic liquids. 
     The phase-change material  28  absorbs heat from the lubricating fluid by changing phase. For example, when the temperature of the lubricating fluid reaches a melting point of the phase-change material, the material changes from a solid to a liquid. Unlike conditions that do not involve a phase-change, the temperature of the phase-change material does not increase as a result of absorbing the heat. Likewise, when the temperature of the lubricating fluid falls below the melting point, the material changes from a liquid to a solid while releasing heat. Because the phase-change material does not change in temperature as it absorbs or releases heat, it is particularly effective in controlling the temperature of the lubricating fluid within a narrow temperature range. The composition of the phase-change material can be adjusted such that the melting point is between the normal operating temperature and a maximum operating temperature of the lubricating fluid. For example, between 130-135 degrees Celsius. Alternatively, a phase-change material may be selected that transitions from liquid state to gaseous state at the desired operating temperature. Use of the phase-change material  28  reduces the quantity of fluid necessary to avoid unacceptable temperature increases during periods of peak demand. Reducing the fluid quantity allows the fluid to warm to normal operating temperature more quickly and reduces parasitic pumping losses. 
     In the embodiment of  FIG. 3 , the heat absorber  26  is mechanically attached to the cover  20  intersecting the central axis  22 .  FIG. 3  is a cross-sectional view of the axle assembly taken along lines  2 - 2  of  FIG. 1 . In this embodiment, ring gear  16  pumps the lubricating fluid across the heat absorber  26 . Specifically, heat absorber  26  may be attached to the cover  20  between 15° above and 30° below central axis  22 . Heat absorber  26  may have a plurality of protrusions  36  extending from a first surface  38  of the heat absorber  26 . The protrusions  36  may be spaced at regular intervals on a first surface  38  of the container  26 . The protrusions  36  increase the surface area available for convective heat transfer between the lubricating fluid and the heat absorber  26 . The protrusions  36  may also contain the phase-change material  28 . Therefore, when the lubricating fluid contacts the protrusions  36 , the phase-change material  28  in the protrusion  36  may further aid to dissipate heat from the lubricating fluid. 
     Although the protrusions  36  are depicted in  FIG. 3  as having a cylindrical cross-section, the protrusions have other cross-sectional shapes such as rectangular. The protrusions  36  are defined vertically at regular intervals. For example, the protrusions  36  may be vertically spaced apart proximate an outer periphery  42  of heat absorber  26 . Likewise, the protrusions  36  may be vertically spaced apart proximate an inner periphery  44  of heat absorber  26 . The protrusions  36  may define a single column along the outer periphery  42 , the inner periphery  44 , or about a vertical centerline of heat absorber  26 . The protrusions  36  may also utilize a multiple column configuration. For example, the protrusions  36  may be formed proximate the outer periphery  42  as well as the inner periphery  44  in a dual column configuration. A dual column configuration is depicted in  FIG. 3 . 
     As depicted in  FIG. 3 , the protrusions  36  defined adjacent the outer periphery  42  are more numerous than the protrusions  36  defined adjacent the inner periphery  44 . It is also contemplated that the protrusions  36  defined adjacent the inner periphery  44  are more numerous than the protrusions  36  defined adjacent the outer periphery  42 . And further, the protrusions  36  adjacent the outer periphery  42  are defined having a greater distance between the protrusions  36  relative to the protrusions  36  defined adjacent the inner periphery  44 . It is also contemplated that the protrusions  36  adjacent the inner periphery  44  are defined having a greater distance between the protrusions  36  relative to the protrusions  36  defined adjacent the outer periphery  42 . In at least one other embodiment, the protrusions  36  in a dual column configuration may be defined with equal spacing and equal number along the outer periphery  42  and the inner periphery  44 . With equal spacing, the protrusions  36  may be defined substantially horizontal across the first surface  38  from the outer periphery  42  to the inner periphery  44 . 
     The described dual column configuration as shown in  FIG. 3  directs the lubricating fluid in an S-pattern across the first surface  38  of the container  26 . Directing the lubricating fluid through the dual column configuration, shown in  FIG. 3 , alternates contact with the protrusions  36 . By alternating contact between the protrusions  36 , the container  26  increases contact with the lubricating fluid along the first surface  38 . As stated above, increasing contact between the first surface  38  and lubricating fluid further controls the amount of thermal energy dissipated to the phase-change material  28  and ensures the lubricating fluid does not exceed a predefined temperature. 
     The heat absorber  26  further includes a port  46  defined on the first surface  38  to allow access to the phase-change material  28 . The port  46  permits changing the phase-change material  28 . As stated above, the phase-change material  28  may be a variety of different materials. Depending on vehicle applications, differing phase-change materials  28  may be used to establish different temperature thresholds. Likewise, the port  46  allows for a combination of phase-change materials  28  to be used within the container  26 . Allowing for a combination of phase-change materials  28  also allows for further control of the predefined temperature threshold for the lubricating fluid depending on vehicle application. 
     The cover  20  further includes an access panel  48  which provides access to the heat absorber  26  for servicing. The access panel  48  eases maintenance and reduces manufacturing costs associated with the installation of the heat absorber  26  on the cover  20 . The access panel  48  may also reduce manufacturing and installation time of the differential housing  40 . Likewise, the access panel  48  allows for removal of the heat absorber  26 . Removing the heat absorber  26  allows for standardization of the housing  40 . A single housing  40  may be used with vehicles in which it may be advantageous to install the heat absorber  26  and use the phase-change material  28  as well as with the vehicles in which it may be advantageous to remove the heat absorber  26 . The access panel  48  further adds to the adaptability and serviceability of the housing  40 , including the cover  20 , the heat absorber  26 , and the phase-change material  28 . 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.