Abstract:
A final drive transmission includes concentric inner and outer metal face seals at an interface between fixed and rotating housing sections for preventing oil contaminating material from entering the housing. Each face seal includes identical metal face seal rings that are biased into sealing engagement with each by identical frusto-conical elastomeric rings. The metal rings are generally L-shaped in cross section, with the metal rings of the outer face seals being constructed to withstand extreme conditions by making their cross section approximately twice that of the inner metal rings. Together with interface surfaces, the assembled inner and outer face seals define a sealed cavity which contains lubrication oil. A reservoir of oil with an oil level sensor is coupled to the sealed cavity and in this way it is determined whether or not oil is leaking from the cavity so that steps may be taken to avoid a catastrophic failure.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to sealing arrangements for final drive gear transmission housings exposed to severe operating conditions. 
       BACKGROUND OF THE INVENTION 
       [0002]    Final drive transmissions, commonly referred to as final drives, for off-road equipment, such as industrial and agricultural tractors are designed with sealed housings for containing lubrication oil for various drive components located within the housings, but are often physically located in an area on the vehicle where it is difficult to detect whether or not the lubrication oil is leaking from the housings. When these final drives are operated in extreme cold weather, it is common for face seals provided for sealing the interface between fixed and rotatable sections of the housings to fail and to leak lubrication oil. No matter what causes a seal to fail, a final drive operated after the lubrication oil has leaked to a low level will often experience a catastrophic failure. This results in large repair costs and down time for the customer. 
         [0003]    What is needed then is a robust seal arrangement for use in final drives and a way to easily detect an oil leak in the event that the seal arrangement fails and leaks. 
       SUMMARY OF THE INVENTION 
       [0004]    According to the present invention, there is provided an improved final drive seal arrangement having one or more features optimized to promote longer effective life together with a remote oil level sensing arrangement for detecting lubrication oil leakage. 
         [0005]    The improved final drive seal arrangement includes an outer face seal assembly including a relatively large diameter annular recesses defining right angle elastomeric load ring seats, and a smaller similar inner face seal assembly located concentric to the larger outer face seal assembly so as to define a sealed lubrication oil cavity between the outer and inner face seal assemblies, with the outer face seal assembly including at least one of the following optimized features:
   a) each elastomeric load ring being frusto-conical and having a dirt excluder lip engaging the OD of the associated metal seal ring to prevent material from entering into the sealed area between the load ring and metal seal ring;   b) anti-rotation lugs to prevent the metal ring from rotating relative to the associated elastomeric load ring member;   c) sealing ribs at the OD of the elastomeric load ring member to prevent material from being forced between the load ring and its seat and down into the seal cavity; and   d) heavy section metal face seal ring members for withstanding forces created during extreme operating conditions.   
 
         [0010]    The sealing arrangement may further include an oil reservoir with an oil level sensor coupled to the lubrication oil cavity and may include a flush port coupled to the sealed lubrication oil cavity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The sole FIGURE is a sectional view taken through a final drive transmission housing and showing the sealing arrangement for forming an annular lubrication oil cavity to which is coupled a remote lubrication oil reservoir having an oil level sensor. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]    Referring now to the drawing, there is shown a longitudinal sectional view of a final drive gear housing  10  forming one of a pair of final drive gear housings of an off-road machine (not shown). The final drive gear housing  10  comprises a split housing including a fixed housing section  12  having a rightward portion defined by a spindle  14 , and a rotatable housing section defined by a wheel hub  16 . 
         [0013]    As viewed in the drawing, an upper left region of the fixed housing section  12  defines a brake housing  18  containing a stack of brake discs  20 , some of which are mounted to the housing  18  for shifting axially and are interleaved with other discs coupled to an exterior of an enlarged right end region of an input collar for rotation with an input collar  22  having an internal end region formed with splines  24  adapted for connection to a splined end of an input shaft (not shown), the input collar having an internal right end region provided with splines coupled for to a externally splined left end region of a shaft forming a left end continuation of a hub of an input gear  26 . The input gear  26  is meshed with a gear  28  received on, and fixed for effecting rotation of, a shaft forming a left extension of a sun gear  30  meshed for driving planet gears  32  carried by a planet carrier  34 , the planet gears  32  being meshed with teeth of a ring gear  36  surrounding the carrier  34 . The carrier  34  is coupled to a left end region of an output shaft  38  disposed in axial alignment with, and rotatably supporting a stub shaft formed at a right side of the sun gear  30 . The output shaft  38  is located centrally within and extends axially through the spindle  14 . A right end region of the output shaft  38  has a sun gear  40  received thereon for being driven by the shaft, the sun gear  40  being meshed with planet gears  42  mounted to a carrier  44  defined by a right end plate of the wheel hub  16 . The planet gears  40  are meshed for traveling about internal teeth of a ring gear  46  having a hub  48  received on and fixed to an exterior right end region of the spindle  14 . 
         [0014]    The wheel hub  16  includes a thick left side region provided with a central opening  50  having right and left regions into which outer races of identical right and left roller thrust bearings  52  and  54  are respectively pressed, the inner races of the bearings  52  and  54  being respectively pressed onto that portion of the ring gear hub  48  which is mounted on the right end region of the spindle  14  and onto an annular shoulder of the spindle  14 . Thus, the bearings  52  and  54  serve to mount the wheel hub  16  for rotation about the longitudinal axis of the output shaft  38 , noting that the hub  16  is driven in rotation by the output shaft  38  acting through the planetary gear set  40 ,  42  and  46  which causes rotation of the carrier  44  and hence the wheel hub  16  which includes the carrier. 
         [0015]    The spindle  14  includes a left end region that extends radially outwardly just to the left of the left thrust bearing  54  and that includes an annular right surface disposed in confronting relationship to a left surface of the wheel hub  16 . This right surface of the spindle  14  and left surface of the wheel hub  16  thus define an interface region that is located radially outward of the left thrust roller bearing  54 , and provided for sealing this interface to prevent leakage of lubrication oil surrounding the bearing  54  and prevent debris from entering from outside the gear housing and contaminating the lubrication oil contained within the gear housing  10  for lubricating the various gears and bearings located within the housing is a sealing arrangement  60 . The sealing arrangement  60  includes an inner face seal assembly  62  that provides a secondary seal to maintain proper oil level in final drive housing  10  for lubricating the various gear sets and bearings located within the housing, and an outer face seal assembly  64  that is exposed to, and provides a primary seal for preventing external material, including abrasive particulate matter, for example, from entering the housing  10 . The inner and outer face seal assemblies  62  and  64 , respectively, each comprise right and left identical elements arranged as mirror images of each other. 
         [0016]    Specifically, the inner face seal assembly  62  is located in an inner annular seal cavity  66  located just radially outward of the left thrust roller bearing  54 . The seal assembly  62  comprises an inner left annular recess  68  provided in a rightward facing surface of the spindle  14  and a right inner annular recess  70  provided in a leftward facing surface of the hub  16 . The inner face seal assembly  64  includes identical left and right metal face seal rings  72  and  74 , respectively, located mostly within the right and left inner annular recesses  68  and  70 . The seal rings  72  and  74  are L-shaped in cross section and each has radial and axially extending legs joined together so as to define an inner right-angular seat, respectively for inner ends of left and right frusto-conical elastomeric load rings  76  and  78 , with outer ends of the left and right load rings being respectively seated in left and right outer right-angular seats respectively defined by radial and axial wall surfaces of each of the left and right recesses  68  and  70 . The elastomeric load rings  76  and  78 , when installed as illustrated, are compressed between their respective inner and outer seats and act so as to exert a biasing force keeping annular sealing surfaces of the metal seal rings in sealed engagement with each other. Further, each of the elastomeric load rings  76  and  78  also performs a sealing function. 
         [0017]    The outer face seal assembly  64  is located in an outer annular seal cavity  80  located radially outward of the inner seal cavity  66  and joined thereto by an annular connecting passage  82  defined by a clearance gap between confronting planar interface surfaces respectively of the fixed spindle  14  and the rotatable wheel hub  16 . The outer annular seal cavity  80  comprises an outer right annular recess  84  provided in a leftward facing surface of the rotatable wheel hub  16 , and a left outer annular recess  86  provided in a rightward facing surface of the fixed spindle  14 . The outer face seal assembly  64  includes identical right and left metal face seal rings  88  and  90 , respectively, located mostly within the right and left outer annular recesses  84  and  86 . The metal face seal rings  90  and  92  are L-shaped in cross section and each has radial and axially extending legs joined together so as to define an inner right-angular seat. Respectively seated against the right angular seats of the face seal rings  90  and  92  are inner ends of right and left frusto-conical elastomeric load rings  92  and  94 , with outer ends of the load rings  92  and  94  being respectively seated in right and left outer right-angular seats respectively defined by radial and axial wall surfaces of each of the right and left outer recesses  84  and  86 . When installed, as illustrated, the load rings  92  and  94  are compressed between their respective inner and outer seats and act to exert a biasing force keeping the annular sealing surfaces of the metal seal rings  88  and  90  in sealed engagement with each other. The elastomeric load rings  92  and  94  include respective annular sealing lips  96  and  98 , respectively, that are in engagement with outer annular surfaces defined by the radial legs of the metal face seal members  88  and  90 , the lips performing a sealing function preventing debris from moving between the load rings  92  and  94  and the radial legs of the associated metal face seal rings  88  and  90 . 
         [0018]    The outer annular seal cavity  80  is exposed to the outside environment by a labyrinth or stepped annular path  100  having an outer section defined by a gap between an inner diameter of an annular ring  102  and an annular outer surface  104  of the spindle  14 . The ring  102  has an annular outer right face portion fixed against a complementary left surface region of the hub  16 , which joins a stepped recess  106  of the hub. The spindle  14  has an annular flange  108  joined to the annular surface  104  and having a left surface spaced from an inner right surface region of the ring  102  so as to define a first intermediate section of the path  100 , having an outer annular surface spaced from one wall of the stepped recess  106  to define a second intermediate section of the path  100 , and having a right face spaced from a second wall of the stepped recess  106  so as to define an inner section of the path  100  that ends at the outer seal cavity  80 . 
         [0019]    In the event that external material does make its way to the seal cavity  80  by way of the path  100 , the seal lips  96  and  98  will tend to prevent the material from making its way between mating surfaces of the elastomeric load rings  92  and  94  and the metal face seals  88  and  90 , noting that the presence of such material has the deleterious effect of rigidifying the action of the elastomeric load rings so that they do not effectively keep the metal face seal rings  88  and  90  properly sealed against each other, especially in severe operating conditions in very cold weather. Also, it is noted that the outer metal face seal rings  88  and  90  are specially constructed to withstand forces created during operation in such severe working conditions by making them more rigid by increasing their cross section, here done by making the cross section of their axial legs approximately twice that of their horizontal legs, the area of the cross section of the outer metal face seal rings  88  and  90  being about twice the area of the cross section of the inner metal face seal rings  72  and  74 . 
         [0020]    An annular sealed cavity  110  is defined between the inner and outer face seal assemblies  62  and  64 , respectively, and an external port, containing a threaded plug  112 , is connected to the sealed cavity  110  and provides access for flushing and cleaning the cavity. 
         [0021]    Also coupled to the sealed cavity  110 , as by an oil line  114 , is an oil reservoir  116  containing oil to a full level L. An oil level sensor  118  located in a side of the reservoir  116  for sensing when the oil level has fallen below the full level L, which indicates that the volume of oil in the cavity  110  has decreased indicating that leakage from the cavity  110  has occurred through at least one of the inner and outer face seal assemblies  62  and  64 . The sensor  118  can be of any known type for completing an electrical circuit or generating an electrical signal for energizing a visual and/or audible warning device  120  to notify an operator of the fact that oil is leaking from the cavity  110 . 
         [0022]    In operation, the larger outer seal assembly  64  will be the most likely to fail due to it being exposed to extreme operating conditions. However, if either of the inner and outer seal assemblies  62  and  64  starts to leak, oil will be lost from the annular oil cavity  110  defined between the seal assemblies  62  and  64 , with this lost oil being immediately replaced by oil from the reservoir  116 . Thus, the oil level in the reservoir  116  will begin to recede from the full level L, with the oil level sensor  118  acting to initiate an energization of the warning device  110  so that an operator is apprised of leakage prior to the amount of leaked oil being of such quantity as to result in a catastrophic failure of gears and/or bearings contained in the final drive housing  10 . 
         [0023]    Although the outer seal assembly  64  is constructed robustly and the stepped passage  100  leading to the seal assembly  64  is sized, so as to minimize external material being forced through the outer seal assembly  64  during operation, some external material will be forced through the outer seal assembly  64 . When this happens, the material forced through the outer seal assembly  64  will become collected and trapped in the annular oil cavity  110 . The threaded plug  90  can periodically be removed to permit this trapped material to be flushed from the cavity  110  before it can pass through the inner face seal assembly  62  to the interior of the final drive housing  10  and damage gears, bearings, etc. 
         [0024]    Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.