Abstract:
The invention is a device for controlling the temperature and thus the viscosity of the lubricating fluid in a rear axle or differential. A first embodiment of the device comprehends a curved bi-metal strip or plate disposed proximate the ring gear and closely conforming to it. The strip extends about the periphery of the ring gear in the direction of rotation of the gear when the vehicle is moving forward. As the temperature of the lubricating fluid increases or decreases, the bi-metal strip or plate moves to direct a larger or smaller flow of the lubricating fluid toward the housing through which heat is transferred to the atmosphere. In another embodiment, a bi-metal baffle disposed adjacent the ring gear includes a plurality of flaps which open upon a rise in lubricating fluid temperature and direct more fluid to the housing to assist heat dissipation.

Description:
FIELD 
     The present disclosure relates to rear axles or differentials and more particularly to a device for controlling or stabilizing the temperature of lubricating fluid in a rear axle or differential. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     The power train in a conventional rear wheel drive vehicle includes a rear axle or differential having a gear set which changes the power flow rotational axis from longitudinal to transverse and four caged bevel gears which allow the wheels and axles to rotate at different speeds when, for example, the vehicle is turning. Many four wheel drive vehicles also utilize a differential in the front axle for the same purpose. 
     Maintaining proper lubrication in the rear axle or differential, particularly the hypoid gear set, is both critical and challenging. Lubrication of the hypoid gear set is essentially achieved by rotation of the ring gear through the lubricating fluid which fills the lower portion of the differential housing. Lubricating fluid is carried by and between the gear teeth and into the region of mesh with the pinion or worm gear. The speed of the ring gear and the viscosity of the lubricating fluid determine how much lubricating fluid will be carried by the ring gear and thus available to lubricate the mesh as well as how vigorously the fluid will circulate within the axle housing. 
     Since the speed of rotation is directly related to vehicle speed, it is essentially an uncontrolled variable. The viscosity of the lubricating fluid is related to its temperature and this may vary significantly in the course of vehicle operation. The viscosity of the lubricating fluid should be high enough to form a film at the mesh thick enough to separate mating surfaces to avoid scoring or abrasive wear. Higher fluid viscosities are thus preferable as they ensure that more fluid will be carried by the ring gear teeth to the mesh. Viscosities that are too high, however, contribute to frictional and churning losses which can account for a significant portion of the energy loss in a differential. The problem of energy loss due to high viscosity is particularly acute during start ups in cold environments. 
     From the foregoing, it is apparent that improvements in rear axles and differentials to provide improved gear lubrication and reduced frictional losses through improved viscosity control would be desirable. 
     SUMMARY 
     The present invention is a device for controlling the temperature and thus the viscosity of the lubricating fluid in a rear axle or differential. A first embodiment of the device comprehends a curved bi-metal element such as a strip or plate disposed proximate the ring gear and closely conforming to it. The strip or plate is secured to a housing of the rear axle or differential and extends about the periphery of the ring gear in the direction of rotation of the gear when the vehicle is moving forward. At lower temperatures or from a cold start, the bi-metal strip closely conforms to the periphery of the ring gear and thus returns lubricating fluid that the ring gear is carrying back to the sump. This direct recirculation raises the temperature of the fluid as quickly as possible. As the temperature of the lubricating fluid rises, the bi-metal strip straightens and moves away from the ring gear allowing the fluid carried by the ring gear to disperse and spray over the inside walls of the differential housing and cool by transferring heat to the ambient. This action becomes more pronounced as the temperature rises and the speed of the ring gear increases—both conditions requiring increased heat dissipation through the walls of the differential housing to lower the temperature of the lubricating fluid. 
     In another embodiment, which may be utilized with or independent of the first embodiment described above, a curved bi-metal strip or baffle is disposed between the ring gear and the rear cover of the differential housing. The baffle includes a plurality of bi-metal louvers or flaps that move from a first, closed position to a second, open position as the temperature of the differential lubricating fluid increases. In the closed position, the lubricating fluid circulates with the ring gear such that the rotating motion and friction warm the fluid. In the second position, the louvers or flaps open windows or apertures that allow the lubricating fluid to contact the inner wall of the rear cover of the housing and dissipate heat to the ambient. 
     It will thus be appreciated that a differential lubrication temperature stabilizer or controller according to the present invention provides a substantially passive device that enhances warmup of the lubricating fluid and adjusts heat dissipation through the differential housing to stabilize the temperature of the lubricating fluid and its viscosity. 
     It is thus an object of the present invention to provide a device for stabilizing the temperature of the lubricating fluid in the rear axle or differential of a motor vehicle. 
     It is a further object of the present invention to provide a device for stabilizing the viscosity of the lubricating fluid in the rear axle or differential of a motor vehicle. 
     It is a still further object of the present invention to provide a bi-metal device for controlling the temperature of the lubricating fluid in the rear axle or differential of a motor vehicle. 
     It is a still further object of the present invention to provide a bi-metal device for controlling the viscosity of the lubricating fluid in the rear axle or differential of a motor vehicle. 
     It is a still further object of the present invention to provide a substantially passive device for controlling the temperature of the lubricating fluid in the rear axle or differential of a motor vehicle. 
     It is a still further object of the present invention to provide a substantially passive device for controlling the viscosity of the lubricating fluid in the rear axle or differential of a motor vehicle. 
     It is a still further object of the present invention to provide a bi-metal device comprehending a curved strip which moves away from a ring gear of a differential as its temperature increases. 
     It is a still further object of the present invention to provide a bi-metal device comprehending a curved baffle having a plurality of flaps which move to open a like plurality of apertures as its temperature increases. 
     Further objects and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic view of a rear axle or differential of a motor vehicle with a portion cut away to show the present invention; 
         FIG. 2  is a side elevational view of a hypoid gear set of a rear axle or differential incorporating the temperature controller of the present invention at a low temperature; 
         FIG. 3  is a side elevational view of a hypoid gear set of a rear axle or differential incorporating the temperature controller of the present invention at a high temperature; 
         FIG. 4  is a full sectional view of a rear axle of differential of a motor vehicle illustrating another embodiment of the present invention; 
         FIG. 5  is an enlarged, fragmentary sectional view of another embodiment of the present invention at a low temperature; 
         FIG. 6  is an enlarged, fragmentary sectional view of another embodiment of the present invention at a high temperature. 
         FIG. 7  is an enlarged, fragmentary sectional view of the louvers or flaps of another embodiment of the present invention taken along line  7 - 7  of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     With reference now to  FIGS. 1 and 2 , a portion of a rear axle of a motor vehicle drive line is illustrated and designated by the reference number  10 . The rear axle assembly  10  includes an elongate housing  12  including a pair of oppositely extending, co-axial axle housings  14  which receive and support a like pair of rear axles or half shafts  16 . The rear axle assembly  10  also includes a bulbous center housing  18  containing a rear differential assembly  20 . It will be appreciated that while described herein as a rear differential, as this will be the more common application, the present invention is equally suited, adaptable and usable in a front axle or differential of a motor vehicle. 
     The rear differential assembly  20  includes a hypoid gear set  22  having a worm or drive gear  24  which rotates about a longitudinal axis of the vehicle. Although described herein in association with a hypoid gear set  22 , it should be appreciated that the present invention is equally suitable and usable with a bevel gear set. The worm or drive gear  24  is coupled to a stub shaft  26  which extends out of the center housing  18  and terminates at a coupling, flange or portion of a universal joint  28 . The worm or drive gear  24  is in constant mesh with and drives a hypoid ring gear  30  which rotates about a transverse axis of the vehicle. The hypoid ring gear  30  is coupled to and drives a differential cage  32  which supports and positions four bevel gears. A first opposed pair of the bevel gears  34 A which rotate on the axis of the hypoid ring gear  30  are secured to and drive a respective one of the rear axles or half shafts  16 . A second opposed pair of the bevel gears  34 B are idler gears and both mesh with both of the first pair of bevel gears  34 A. The differential cage  32  and the first and second pairs of bevel gears  34 A and  34 B operate in conventional fashion to allow differential rotation of the rear axles or half shafts  16  (and associated tire and wheel assemblies which are not illustrated) as the motor vehicle turns or corners. The center housing  18  which receives the just-described components acts as a sump and is filled, typically about half way, with gear lubricating fluid  36 . 
     Referring now to  FIG. 2 , also disposed within the center housing  18  is a lubricating fluid temperature controlling or stabilizing assembly  40 . The lubricant temperature controlling or stabilizing assembly  40  includes a curved bi-metal or bi-metallic element such as a strip or plate  42 . The element  42  may also be referred to as bi-thermal since it includes materials having two distinct thermal coefficients of expansion. The bi-metal strip or plate  42  comprises two relatively thin strips of distinct materials, preferably metals, having different thermal coefficients of expansion. Typically, steel and copper are utilized although other metals, alloys and materials are suitable. The two strips of metal are intimately bonded together by, for example, brazing or welding or an adhesive. The metal or material having the higher coefficient of thermal expansion forms or constitutes the concave side or inner component  42 A of the strip or plate  42  and the metal or material having the lower coefficient of thermal expansion forms or constitutes the convex side or outer component  42 B of the strip or plate  42 . Thus, the inner component  42 A is preferably copper and the outer component  42 B is preferably steel. 
     The bi-metal strip or plate  42  is secured to the inside surface  44  of the center housing  18  or a suitable boss or projection on the inside surface  44  by a fastener  46  such as a rivet, threaded fastener or stake. Preferably, the fastener  46  and the secured end of the bi-metal strip or plate  42  are disposed approximately at the upper level of the lubricating fluid  36 . In a quiescent, ambient temperature condition, for example, 68 degrees Fahrenheit (20 degrees Celsius), the bi-metal strip or plate will be shaped and configured to conform closely to the periphery of the ring gear  30 . Depending upon the characteristics of the lubricating fluid  36  such its viscosity and the variation of viscosity with temperature, the thermal coefficients of expansion of the materials utilized to form the bi-metal strip or plate  42  and other design and performance parameters, this temperature at which the bi-metal strip  42  conforms to the periphery of the ring gear  30  may vary over a significant range, for example, from 32 degrees Fahrenheit (0 degrees Celsius) or lower to 100 degrees Fahrenheit (38 degrees Celsius) or higher. 
     From its point of attachment by the fastener  46 , the bi-metal strip  42  curves around the ring gear  30  in the direction of its rotation when the vehicle is moving forward. Therefore, as illustrated in  FIG. 2 , the axles  16  and the ring gear  30  rotate clockwise as viewed from the left side when the vehicle is moving forward as indicated by the arrows. Thus the bi-metal strip or plate  42  curves around the ring gear  30  from the side opposite the worm or drive gear  24  toward the front of the center housing  18 . 
     The bi-metal strip or plate  42  includes a stop or bumper  48  that engages a flange or projection  52  extending from the inner surface  44  of the center housing  18 . Contact between the stop or bumper  48  and the projection  52  limits inward translation or the bi-metal strip or plate  42 , i.e., travel toward the ring gear  30 , to prevent contact between the strip or plate  42  and the ring gear  30 . The stop or bumper  48  affects and contributes to the operation of the bi-metal strip  42  since it establishes a minimum, low temperature position below which no additional motion toward the ring gear  30  will occur. Viewed from the opposite operational perspective, contact between the stop or bumper  48  and the projection  52  may be adjusted to ensure that no motion of the bi-metal strip or plate  42  away from the ring gear  30  occurs until the temperature of the lubricating fluid  36  has increased to a particular temperature. The bi-metal strip or plate  42  has a width at least as wide as, and preferably wider than, the nominal width of the ring gear  30 . If desired, the bi-metal strip or plate  42  may include thin, inwardly directed sidewalls (not illustrated) which extend toward the ring gear  30  and define a shallow channel or groove which receives the ring gear  30 . Such a channel or groove enhances the ability of the ring gear  30  to collect and carry lubricating fluid  36  as it rotates. 
     In operation, the lubricant temperature stabilizing or controlling assembly  40 , if beginning from a cold or ambient temperature start, will be in the position illustrated in  FIG. 2 , that is, closely conforming to the periphery of the ring gear  30 . In this position and temperature state, the stop or bumper  48  may be engaging the flange or projection  52  to prevent the bi-metal strip or plate  42  from translating into contact with the ring gear  30  due to the low temperature. So disposed, as the ring gear  30  begins to rotate as the vehicle moves, lubricating fluid  36  that is carried by and between the gear teeth of the ring gear  30  will be directed back to the sump in the center housing  18  and, to the extent possible, be warmed by the mechanical motion, friction and meshing of the worm gear  26  and the ring gear  30 . 
     Referring now to  FIG. 3 , after the differential assembly  20  has operated for a period of time, and the temperature of the lubricating fluid  36  has risen, the bi-metal strip or plate  42  will begin to straighten and move away from the ring gear  30 . As it does so, as the speed of the ring gear  30  increases and as the viscosity of the lubricating fluid  36  reduces, an increasing flow of the lubricating fluid  36  is directed toward the inner surface  44  of the center housing  18 . This redirected flow of lubricating fluid  36  transfers heat from the lubricating fluid  36  to the center housing  18  and thence to the ambient. 
     From the foregoing, it will be appreciated that if the temperature of the lubricating fluid  36  begins to fall due, for example, to changed weather or vehicle activity, the bi-metal strip or plate  42  will begin to curve back toward the ring gear  30  thus lessening the flow of lubricating fluid  36  directed to the inner surface  44  of the center housing  18  and reducing the heat transfer to the center housing  18  and the ambient. In this manner, the temperature of the lubricating fluid  36  is stabilized, i.e., rendered more constant, by linking the rate of heat dissipation to the temperature of the lubricating fluid  36 . 
     When the vehicle has been inactive for a period of time and the lubricating fluid  36  in the center housing  18  has cooled, the bi-metal strip or plate  42  returns to the position illustrated in  FIG. 2 . 
     Referring now to  FIG. 4 , another embodiment of the lubricating fluid temperature controlling or stabilizing assembly according to the present invention is illustrated and designated by the reference number  60 . It will be appreciated that the assembly  60  is also utilized with a housing  18  of a differential assembly such as a rear differential assembly  20  having a hypoid gear set  22  including a worm or drive gear  24  mounted on a stub shaft  26  which terminates in a flange or universal joint  28 . A ring gear  30  is in constant mesh with the worm gear  24  and drives, through a conventional caged bevel gear set (not illustrated), a pair of axles or half shafts  16  (one of which is illustrated). 
     The housing  18  includes a rear cover or plate  58  which is secured thereto by a plurality of threaded fasteners such as bolts (not illustrated). The lubricating fluid temperature controlling or stabilizing assembly  60  includes a curved strip or baffle  62  which is disposed between the ring gear  30  and the rear cover  58  of the differential assembly  20  and which preferably conforms to the curvature of the ring gear  30 . The baffle  62  is fabricated of a bi-thermal material, preferably two metals having distinct thermal coefficients of expansion and typically, copper and steel. 
     Referring now to  FIG. 5 , the curved strip or baffle  62  includes a first or outer layer  62 A of a material, typically a metal, having a higher thermal coefficient of expansion and a second or inner layer  62 B of a material, typically a metal, having a lower thermal coefficient of expansion. The two layers  62 A and  62 B are intimately bonded by welding, brazing or other securement method. The outer layer  62 A is preferably copper and the inner layer  62 B is preferably steel although many other metals and alloys having the necessary thermal characteristics may be utilized. 
     The curved strip or baffle  62  defines a plurality of louvers or flaps  64 . The louvers or flaps are small panels defined by three sided or U-shaped cutouts which free a bottom and two side of the louvers or flaps  64  which are secured to the baffle  62  along one edge  66 . Opposite the edge  66 , the louvers or flaps  64  may include a beveled or chamfered edge  68  which streamlines fluid flow thereover. In  FIG. 5 , the louvers or flaps  64  are shown in a cold or low temperature condition. As such, the louvers or flaps  64  conform generally to the overall curve of the strip or baffle  62  and prevent flow of the lubricating fluid  36  through the baffle  62 . The “R” and arrow indicate the direction of rotation of the ring gear  30  both here and in  FIG. 6 . 
     In  FIG. 6 , the louvers or flaps  64  are shown in a hot or operating temperature condition. Here, the louvers or flaps  64  have curved inwardly and opened a plurality of apertures or windows  72  through which the lubricating fluid  36  may flow so that it will contact the rear cover  58  of the housing  18  and transfer heat to the ambient. It will be appreciated that the particular temperature to louver or flap movement relationship may be established by experimental and empirical study to best match the goals of performance, lubrication and energy efficiency. 
       FIG. 7  generally illustrates the alignment of the strip or baffle  62  with the ring gear  30  as well as their relative widths. It will be noted that the strip or baffle  62  is generally centered upon and is significantly wider than the ring  30  gear and that the louvers or flaps  64  are somewhat wider than the ring gear  30 . 
     The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.