Abstract:
A system for regulating lubricant temperature within a vehicle axle is provided. A differential housing has a primary chamber that contains the differential, and a secondary chamber separated from the primary chamber. A sump is in the primary chamber for collecting lubricant. An inlet to the secondary chamber allows the lubricant to flow from the primary chamber into the secondary chamber. An outlet to the secondary chamber allows the lubricant stored therein to be purged into the sump. When the lubricant is below a certain threshold temperature, a temperature-responsive valve is configured to close to inhibit the fluid to travel through the outlet. When the temperature of the lubricant rises to exceed the threshold, the valve is configured to open and permit the fluid to travel through the outlet.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to a differential in an automotive vehicle. More particularly, this disclosure involves a system for removing a portion of the lubricant within a differential to improve churning losses and fuel efficiency. 
       BACKGROUND 
       [0002]    Differentials in motor vehicles have been used for many years to transfer power from one driving member (e.g., drive shaft) to two wheels via axle shafts. Differentials can include rings gears that engage corresponding gears of the driving member to change the direction of the rotational force. The ring gears typically operate with lubricant to reduce friction and heat with the meshing parts. 
       SUMMARY 
       [0003]    According to one embodiment, a system for regulating lubricant temperature within a vehicle axle is provided. The system includes a housing having a primary chamber containing a differential, a sump in the primary chamber for collecting lubricant, and a secondary chamber having an inlet for receiving the lubricant from the primary chamber and an outlet for purging the lubricant into the sump. A valve is at the outlet and is configured to open in response to a temperature of the lubricant exceeding a threshold. 
         [0004]    The primary chamber and the secondary chamber may be separated by a wall. The differential may include a ring gear having a perimeter, and the wall may be rounded to follow the shape of the perimeter. 
         [0005]    A shoulder may extend into the primary chamber at the inlet to direct the lubricant into the inlet. 
         [0006]    The valve may be configured to close in response to the temperature decreasing from greater than the threshold to less than the threshold. 
         [0007]    The secondary chamber may be located rearward of the differential in the vehicle and may be at least partially defined by a rearward wall of the housing. The rearward wall may be separately attached to a primary exterior wall that defines the primary chamber. 
         [0008]    According to another embodiment, a vehicle includes a differential and a housing having a primary chamber containing the differential and fluid. A secondary chamber is adjacent the primary chamber and has an inlet in fluid communication with a first region of the primary chamber and an outlet in selective fluid communication with a second region of the primary chamber. A valve is configured to selectively permit fluid to flow through the outlet in response to a temperature of the fluid exceeding a threshold. 
         [0009]    According to yet another embodiment, a method includes operating a ring gear of a differential within a primary chamber of a housing to cause lubricant to enter a secondary chamber of the housing. The method further includes storing the lubricant in the secondary chamber while a temperature of the lubricant is less than a threshold. The method further includes releasing the lubricant from the secondary chamber to the primary chamber in response to the temperature exceeding the threshold. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic of an exemplary vehicle having a differential of the present disclosure. 
           [0011]      FIG. 2  is a cross-sectional view of the differential of  FIG. 1  with any fluid removed to show the mechanical components. 
           [0012]      FIG. 3  is a cross-sectional view of the differential of  FIG. 1  with fluid maintained in a sump of a primary chamber of the differential housing. 
           [0013]      FIG. 4  is a similar cross-sectional view of the differential, with arrows representing rotational movement of a ring gear which causes fluid to splash into a secondary chamber. 
           [0014]      FIG. 5  is a similar cross-sectional view of the differential, with a valve opening to release the fluid from the secondary chamber back into the sump. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    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 embodiments. 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. 
         [0016]      FIG. 1  illustrates one embodiment of a vehicle  10  incorporating the inventive concepts described below. In this embodiment, the vehicle  10  has an engine  12  that delivers power to a transmission  14  to turn a drive shaft  16  that transfers power toward the rear wheels. The transmission  14  can be a step-ratio transmission, a continuously-variable transmission (CVT), or other types known. In other embodiments, the vehicle is a hybrid vehicle that also (or alternatively) includes an electric motor that can provide power to the rear wheels. 
         [0017]    The drive shaft  16  provides power to a differential  20 . In the embodiment shown in  FIG. 1 , the differential  20  is a rear differential that distributes power to the rear left and right wheels  18 . The differential  20  allows the two wheels to spin at different speeds to allow, for example, the vehicle to travel around corners with the outside wheel covering more ground (and therefore spinning faster) than the inside wheel. 
         [0018]    One embodiment of the differential  20  is shown in  FIGS. 2-5 . According to this embodiment, the drive shaft  16  is operative to rotate a pinion gear  24  which, in turn, rotates a ring gear  26 . The pinion gear  24  has teeth which meshingly engage corresponding teeth of the ring gear  26 . This allows rotational power to change directions (e.g., 90 degrees) from the drive shaft  16  and begin flowing toward the wheels. 
         [0019]    The differential  20  is contained within a housing  30 . In one embodiment, the housing  30  includes a first exterior wall  32  and a separate second exterior wall  34  that are joined together during manufacturing via welding, fasteners, etc. In one embodiment, the housing can refer to just the portion of the differential enclosure that is made up of the first exterior wall  32 , and a chamber (as described below) can refer to a separate portion adjacent to the housing. 
         [0020]    During operation of a typical differential, the lubricant inside the differential is splashed forward towards the front head of the differential due to the spinning ring gear being immersed in the lubricant in the sump of the differential. The immersion of the ring gear in the fluid can increase churning losses under low ambient conditions when the fluid viscosity is high. Due to the heightened viscosity, the paddle wheel effect of the ring gear causes an increase in losses in the differential, increasing vehicle fuel consumption. 
         [0021]    According to various embodiments of the present disclosure, a secondary chamber is provided within the differential housing (or adjacent the differential housing). The secondary chamber stores at least some of the splashed lubricant to remove some of the lubricant from the sump to decrease churning losses under low ambient conditions. The lubricant stored in the secondary chamber is released back into the primary chamber in response to the lubricant reaching a predetermined temperature, indicating a lower viscosity of the lubricant and thus more preferable operating conditions. 
         [0022]    According to at least one particular embodiment, the housing  30  defines a primary chamber  36  and a secondary chamber  38 . The primary chamber is a chamber, cavity, pocket, or the like that is sized and configured to contain the differential components such as the ring gear  26 . There is clearance within the walls  32  of the primary chamber  36  to account allow for lubricant to flow therethrough. The secondary chamber  38  is adjacent to the primary chamber  36 . In one embodiment, the primary chamber  36  and the secondary chamber  38  are separated or partitioned by a partition wall  40 . The partition wall  40  may be curved to follow the shape of the ring gear  26 . This directs the lubricant during operation of the differential, as will be described below. 
         [0023]    The secondary chamber  38  is located rearward of the primary chamber  36 , with respect to a rearward direction of the vehicle. This chamber  38  stores lubricant as it is splashed by the ring gear, as will be described below. 
         [0024]      FIG. 3  shows the differential with fluid or lubricant  44  in a bottom portion (e.g., sump  46 ). In this figure, the vehicle is stationary and all of the fluid (save some residual fluid) is held in the sump  46  of the primary chamber  36 . 
         [0025]      FIG. 4  shows the differential being operated in relatively low ambient temperatures causing a relatively high viscosity of the lubricant  44 . As the ring gear  26  spins, some of the lubricant  44  is splashed or otherwise directed over the partition wall  40  and into the secondary chamber  38  through a region defining an inlet  50  of the secondary chamber  38 . This is represented by the arrows shown in the Figure. To aid in directing fluid into the secondary chamber, a curved flange or shoulder  52  extends from the second exterior wall  34 . In some embodiments, the shoulder  52  extends over the partition wall  40  and into the primary chamber  36 . As the ring gear  26  is rotated (counter-clockwise in  FIG. 4 ), the shoulder  52  catches and directs some of the fluid to enter through the inlet  50 . 
         [0026]    A valve  54  is located at an outlet  56  of the secondary chamber  38  at an opposing end of the secondary chamber  38  from the shoulder  52 . The valve  54  selectively inhibits the lubricant in the secondary chamber  38  from re-entering the primary chamber  36 . In one embodiment, the valve  54  remains closed when the temperature of the lubricant is below a predetermined temperature threshold. This removes some of the lubricant from the primary chamber  36  during times of heightened viscosity of the lubricant when temperatures are relatively low. Then, in response to the temperature of the lubricant exceeding the predetermined temperature threshold, the valve  54  opens to allow the fluid to drain back into the primary chamber  36  at the sump  46 . This is shown in FIG.  5 , in which the valve  54  has opened and the sump  46  has re-filled with the lubricant. This allows more of the lubricant to act on the ring gear  26  during times when the viscosity has reduced to preferential operating conditions. 
         [0027]    In one embodiment, the valve  54  is a wax thermostatic element (i.e., wax motor thermostat valve). The thermal properties of the wax in the thermostatic element cause expansion and contraction of the wax itself, which causes a corresponding opening and closing of the valve  54 . The properties of the wax can be such that the valve  54  opens and closes when the surrounding lubricant causes a phase change in the wax at a certain temperature. 
         [0028]    In another embodiment, a separate thermostat is disposed in or around the differential to detect the temperature of the lubricant in the differential. The thermostat sends temperature signals to a controller (e.g., microprocessor) that opens a closes the valve in response to the temperature signals exceeding or falling below associated thresholds. 
         [0029]    The embodiments described above allow a reduced amount of lubricant to be utilized during cold ambient temperature. Then, once the temperature of the lubricant raises, more lubricant can be added to the sump and primary chamber without undesirably high churning losses. The thermostatic element can be tuned based on the lubricant quantity needed to minimize durability issues on the differential. 
         [0030]    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. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, to the extent any embodiments are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics, these embodiments are not outside the scope of the disclosure and can be desirable for particular applications.