Abstract:
A transfer case is provided with a primary shaft which is selectively engagable with a secondary shaft via a clutch mechanism. The clutch mechanism is inclusive of a friction pack. A hub of the clutch mechanism is connected on the primary shaft and the clutch housing is torsionally fixed with a primary sprocket rotatively mounted on the primary shaft. A passive or active controlled lubricant collection receptacle is provided which maximize fluid retention in conditions wherein there is not a high demand of torque for the clutch system of the transfer case thereby minimizing fluid that is unnecessarily churned by engagement with the hub connected with the secondary shaft.

Description:
FIELD OF THE INVENTION 
     The present invention relates to transfer cases for automotive vehicles. In particular, the field of the present invention is for transfer cases for selective on demand four wheel drive vehicles with particular application for vehicles having normal rear wheel drive with longitudinally mounted engines. 
     BACKGROUND OF THE INVENTION 
     Most rear wheel drive vehicles which are selectively engagable to be all wheel drive vehicles have a transfer case. The transfer case typically has a primary shaft which is connected to the output of a vehicle transmission. The primary shaft typically rotatably mounts a sprocket that engages a chain. The chain typically engages with another sprocket that is typically connected with a secondary shaft. The secondary shaft is rotatably mounted within the transfer case. The secondary shaft is torsionally connected with a front drive shaft that is torsionally connected with a front differential to power front wheels of the vehicle. To provide a function of selectively engaging the front wheels of the vehicle, there is provided a clutch mechanism that selectively engages the sprocket on the primary shaft with the primary shaft to transfer torque from the primary shaft to the secondary shaft thereby selectively engaging the front wheels of the vehicle. When ideal pavement conditions exist, typically the clutch will not be engaged so that the transmission only torsionally engages the rear wheels of the vehicle. A controller is typically provided which is cognizant of wheel slip conditions to automatically control the engagement of the clutch. In some four wheel drive embodiments, the clutch can also be engaged as a result of operator demand. 
     In many transfer cases, in the two wheel drive mode of operation, the secondary shaft will still rotate due to the movement of the non-powered (in most cases front) wheels. This condition exists even when the clutch is non-engaged and no torque transfer is occurring to the secondary shaft. 
     Most transfer cases have some type of lubricant pump to provide lubrication for the clutch in its associated friction pack, the shafts, bearings, sprockets and chain. The operation of this pump provides a load on the vehicle engine either mechanically by being powered by the take off from the vehicle drive train or is a load upon the engine indirectly by generating a parasitic electrical load. It is desirable to provide a transfer case wherein the lubrication needs can be provided in a more passive manner from the operation of the transfer case. 
     It is desirable that the amount of lubricant within the transfer case which is exposed to churning by the secondary sprocket be as little as possible to avoid foaming the lubricant and the generation of heat within the lubricant. The above provides higher efficiency of the transfer case when churning of the oil is reduced or minimized. It is desirable to provide a transfer case which maximizes lubricant capacity, minimizes the distance from the sprocket wheel to the bottom of the transfer case and additionally minimizes the amount of fluid exposed to the secondary sprocket during two wheel drive operation or high speed four wheel drive operation wherein there is low torque demands for the wheels connected to the differential connected with the secondary shaft. 
     SUMMARY OF THE INVENTION 
     To meet the above noted desires and to provide other manifold advantages, a revelation of the present invention is brought forth. The present invention in one of its embodiments provides a transfer case with a primary shaft that is selectively engagable with a secondary shaft via a clutch mechanism. The clutch mechanism is inclusive of a friction pack. A hub of the clutch mechanism is connected on the primary shaft and the clutch housing is torsionally fixed with a primary sprocket rotatively mounted on the primary shaft. The transfer case has a lubricant collection receptacle located remotely from a sump underneath the secondary shaft which allows for more lubricant to be stored within the transfer case. Since the receptacle is located away from the sump therefore less lubricant is exposed to the secondary sprocket when the vehicle is in a two wheel drive mode or a high speed four wheel drive mode with low torque demand for the wheels of the vehicle torsionally connected with the secondary shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a sectional view of a transfer case; 
         FIG. 2  is a rear elevational view of the transfer case shown in  FIG. 1 ; 
         FIG. 3  is a front perspective view of the transfer case shown in  FIGS. 1 and 2  with a front cover plate removed; 
         FIG. 4  is a rear perspective view with portions of the transfer case shown phantom in  FIGS. 1-3 ; 
         FIG. 5  is a partial sectional view illustrating a lubrication path extending between the hub and a primary shaft of the transfer case shown in  FIGS. 1-4 ; 
         FIG. 6  is a view of a transfer case functionally similar to that shown in  FIGS. 1-5  providing a lubricant collection receptacle in the loop of the belt which torsionally connects sprockets provided on the primary and secondary shafts of the transfer case; 
         FIG. 7  is a section view taken along lines  7 - 7  of  FIG. 6 ; 
         FIG. 8  is a view similar to that of  FIG. 6  of an alternate preferred embodiment transfer case according to the present invention having an actively controlled lubricant collection receptacle according to the present invention; 
         FIG. 9  is a view similar to that of  FIG. 8  illustrating operation of the actively controlled fluid collective receptacle of the transfer case shown in  FIG. 8 ; 
         FIG. 10  is a view similar to that of  FIG. 3  of an alternate preferred embodiment transfer case according to the present invention having a passively hydraulically actuated valve controlling fluid communication between a lubricant collection receptacle and a friction pack interface between a hub and a clutch housing of a clutch utilized to selectively connect a sprocket on a primary shaft with the sprocket on a secondary shaft according to an alternate preferred embodiment of the present invention; 
         FIG. 11  is a rear perspective view of a transfer case shown in  FIG. 10 ; 
         FIG. 12  is a sectional view taken primarily through the primary shaft of the transfer case shown in  FIG. 10 ; 
         FIG. 13  is a partial section rear view of the transfer case shown in  FIG. 10 ; 
         FIG. 14  is an enlarged section view illustrating a portion of the hydraulically actuated valve controlling fluid communication between the lubricant collection receptacle and the friction pack of the clutch; 
         FIG. 15  is a view similar to that of  FIG. 14  illustrating operation of the fluid actuated valve which controls fluid communication between the lubricant collection receptacle and the friction pack of the clutch of the transfer case shown in  FIG. 10 ; 
         FIG. 16  is a view similar to  FIG. 14  illustrating a valve that is an alternative to the valve shown in  FIG. 14 ; and 
         FIG. 17  is a view similar that that of  FIG. 15  of the valve shown in  FIG. 16 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Referring to  FIGS. 1-5 , an example of a transfer case  7  is provided. The transfer case  7  has a housing  10 . The housing  10  has a front cover plate  12  which is boltably connected to a main body  14 . Rotatably mounted within the transfer case housing  10  is a primary shaft  16 . The primary shaft  16  has a front end  18  conformed to connect with an output shaft (not shown) of a transmission of the vehicle. Typically, the vehicle will be a rear wheel drive vehicle with a longitudinally mounted engine. The drive train for the vehicle is configured in such a way that power can be selectively diverted from the rear axle to be shared with the front axle to provide the vehicle with all wheel drive capabilities. The primary shaft is mounted to the front cover plate  12  by a front bearing  20 . A rearward portion of the primary axle  16  is rotatably mounted within the housing main body  14  by a rear bearing  22 . A rear end  24  of the primary shaft is connected with a yoke  26  by a nut  28  which captures a washer  30 . The yoke  26  is connected with a drive line extending to a vehicle rear differential and axle (not shown). 
     At a lower elevation, the transfer case  7  also rotatably mounts a secondary shaft  34 . The secondary shaft  34  is configured to have in its inner diameter splined teeth  36  to allow the secondary shaft  34  to power either directly or via a universal type joint, a front drive line shaft (not shown) that is torsionally connected with a differential for front wheels of the vehicle. In another embodiment (not shown), the secondary shaft can be connected with a front wheel drive line via a flange connection. An exterior of the secondary shaft is a connected sprocket  38  provided with a series of sprocket teeth  39 . The sprocket teeth  39  engage a flexible torsional force transfer member or a belt  40  (shown schematically) which is typically provided by a multi-link chain. The belt  40  is engaged with sprocket teeth  42  provided on the engagement wheel or primary sprocket  44 . The primary sprocket  44  is rotatably mounted on the primary shaft  16  by needle bearings  46 . In other embodiments (not shown), the primary sprocket can instead be a gear in direct or indirect gear connection with the secondary shaft. 
     To allow the primary shaft  16  to selectively torsionally engage the secondary shaft  36 , there is provided a clutch  50 . The clutch  50  includes a clutch housing  52 . The clutch housing  52  is torsionally fixably connected with the primary shaft sprocket  44 . The clutch housing  52  has a series of radial folds  54  which provide radially inward projecting teeth which engage with correspondingly shaped radial edges of friction discs  56 . The friction discs  56  are intermingled with corresponding friction plates  58 . The friction plates  58  along their inner diameter have a gear tooth type profile to allow them to be torsionally connected with a hub  62  having radially outward corresponding folds. The hub  62  is torsionally affixed with the primary shaft  16  by weld, spline or shrink fit arrangement. A backing plate  64  is also provided. The backing plate  64 , as well as friction plates  58  and friction discs  56 , form a friction pack to allow for selective connection of the clutch housing  52  with the clutch hub  62  thereby causing the sprocket  44  to be joined with the primary shaft  16 . 
     The hub  62  has a multiple series of lubrication axial extending passages  70 . The axial passages  70  are intersected with radially outward projecting lubrication holes passages  72  which deliver lubricant to the friction pack. To selectively engage the friction pack, there is provided a piston  74 . The piston  74  has a radially inner seal  76  and a radially outer seal  78 . Axially behind the piston  74  is a pressurizable chamber  79  which is connected by a passage (not shown) with a source of pressurized fluid (not shown). When actuated, the piston  74  engages a bearing  82  which is adjacent to the backing plate  64  to engage this friction pack thereby torsionally connecting the hub  62  and primary shaft  16  with the sprocket  44 , belt  40  and secondary shaft  34  to torsionally power the front wheels of the vehicle. 
     When torque to the front wheels is required, there is need for lubricant to be delivered to the clutch pack primarily for cooling the friction pack. Lubricant is also delivered to the belt  40  and the sprockets  44  and to the secondary shaft  36 . 
     As the chain moves, lubricant oil is splashed. Much of the oil is splashed into a reservoir system that includes collection baffle  90  having an entrance  92  generally adjacent the primary sprocket  44 . The momentum of the lubricant oil causes the lubricant to be transported in an axial direction above the primary shaft  16  and above axially overlapping the piston  74  the clutch  50  and its associated friction pack. The lubricant is then collected in a lubricant collective receptacle  96 . The fluid receptacle  96  is formed in the body  14  of the housing. The receptacle  96  is stationary. The collection of oil develops a pressure head which enters a stationary housing vertical passage  98 . The vertical passage  98  intersects with the rear bearing  22  to lubricate the same. Intersecting the vertical passage  98  is a stationary housing generally axial passage  100 . Thus the flow of oil is additionally radially inward of the friction pack. Axial passage  100  allows the oil under the pressure heads supplied by the reservoir to travel axially in a generally forward direction flow into an axial extending lubricant passage  70  provided in the hub. One factor which enhances the performance of the lubrication provided by the present invention is that when the lubricant is being transported vertically inward through passage  98  there are no rotating member which it must pass. Oil entering the axial lubrication passage  70 , then through rotation, the oil is urged radially outward through lubrication holes  72  to lubricate the friction pack. 
     Radially inward of the lubrication passage  100  is an inner lubrication passage  101 . Inner lubrication passage  101  intersects with a disc shaped space  103 . The disc shaped space  103  is bordered by a path restriction  112  which prevents lubrication oil from being flung outward to piston  74 . The primary shaft  24  is splined to the hub  62  by a series of radially outward extending teeth  116  interacting with radially inward extending teeth  118  of the hub. One or more of the teeth  116  or  118  are deleted to provide a lubrication passage  114  which extends between the interface of the hub and a primary shaft allowing lubricant to flow from the rear of the hub to the front of the hub and thereby reach needle bearings  46  which rotatively mount the primary sprocket  44  to the primary shaft. 
     Referring to  FIGS. 6 and 7 , a transfer case  207 , having almost identical function and structure to previously described transfer case  7 , is provided. In transfer case  207 , between a loop of the belt or chain  210  provided is an auxiliary reservoir or lubricant collection receptacle  212 . The receptacle  212  is formed by walls  213  and  215  which project from a front portion  217  of the housing and a rear portion  221  of the housing meeting along a line  223 . The collection receptacle  212  has an opening  214 . The opening  214  allows the collection receptacle  212  to gravitationally capture lubricant that is splashed by the primary and secondary sprockets  205 ,  209  and chain  210 . Adjacent the collection receptacle  212  in towards the secondary shaft  216 , the receptacle has a molded or drilled passage  218 . Passage  218  intersects a cross passage  220  (as shown molded, but can be cross bore plugged at extreme ends) and longitudinal passages  222  (as shown molded, but can be blind bores) to provide a path for lubricant within collection receptacle  212  to lubricate the bearings  224  of the secondary shaft in a passive manner. If the secondary shaft is powering the front wheels when the vehicle is at a high rate of speed, lubricant will tend to collect within the collection receptacle  212  faster than it leaks through the passage  218  to lubricate the secondary shaft bearings thereby in a passive manner automatically remove or store lubricant away from the sump which is underneath the secondary shaft  216 . The lubricant collection receptacle  212  can be designed in certain applications to hold 20% or more of the total lubricant capacity of the transfer case is desired. This removal of lubricant from an area adjacent to the shaft  216  in its connected sprocket  226  causes a reduction of churning of the lubricant resulting reducing any foaming or heat generation and increasing transfer case efficiency. 
     Referring to  FIGS. 8 and 9 , transfer case  247  according to the present invention can additionally be provided with an actively controlled lubricant collection receptacle  250  having an open top  252 . The receptacle  250  can be a separate container, or a container formed in full or in part by the frame or other components of the transfer case. The open top gravitationally captures lubricant primarily splashed by the chain  253  (shown in phantom) and the upper sprocket (not shown) and by splash off of the casing walls. Receptacle  252  via a conduit  254  is connected with the bottom of a sump area  256  extending into the secondary shaft. Controlling the flow through the conduit  254  is a solenoid actuated valve shown schematically  258 . 
     During normal operation or operation at slow speeds, spilled lubricant enters into retaining receptacle  250  to the top; over fill lubricant is allowed to flow into the sump to achieve a level within the sump  264 . If the vehicle thereafter goes to a high level speed, in two wheel drive mode, (not needing any torque requirements for the clutch), valve  258  will shut, causing the receptacle  250  to fill up bringing the level of lubricant to that of  266  to avoid or minimize churning of fluid. Churning of lubricant can cause the generation of heat and undesired foaming. Control of the opening of valve  258  can be proportional and can be based upon the rotational speed or derivatives thereof of the secondary shaft which will be proportional generally to the speed of the vehicle. The control of solenoid valve  258  can also be a function of the torque demand placed upon the clutch of a vehicle transfer case. Higher torque demands will allow greater amounts of lubricant to be released by the valve  258 . Typically, the control of the valve  258  will be a function of an electronic control unit. 
     Referring to  FIGS. 10-15 , an alternative preferred embodiment transfer case  307  according to the present invention is provided. The transfer case  307  has a housing  310  with a front cover  312  and a main body  314 . Transfer case  307  has a primary shaft  316  rotatively mounted to the front cover plate  312  by a front bearing  320 . Spline connected to the primary shaft  316  is a hub  362  that is connected to the primary shaft  316  in a manner as previously described and also having an axial extending lubrication passage  383  and is interfaced with the primary shaft  316  as previously described and also having a lubrication passage (not shown) similar to passage  114  (as described for hub  52  in  FIG. 1 ). 
     Rotatably mounted on the primary shaft  316  by needle bearings  346  is a primary sprocket  344 . Primary sprocket  344  is fixably connected with a clutch housing  352 . The clutch housing  352  can be selectively engaged with the primary shaft  316  and hub  362  in a manner as previously described by virtue of a friction pack which can be selectively engaged by a hydraulically extruded piston  374 . The front plate cover  312  has connected thereto a baffle  315 . The baffle  315  is positioned generally adjacent to a chain  340  which transmits torque between a primary sprocket  344  and a secondary sprocket  338 . Transfer case  307  also has a lower slack adjuster  363  which has extending there from two lubricant retainers  335 . The lubricant retainers  335  function to help retain lubricant within the chain  340  as the chain  340  moves from the lower secondary sprocket  338  to the primary sprocket  344 . The lubricant in normal usage being pooled in the bottom of the housing  310 . The clutch housing  352  also has a series of axially spaced holes  353  to allow for the escape of lubricant in the friction pack beyond the clutch housing. The holes  353  are typically be on top of the radial folds  354  of the clutch housing. 
     As the chain  340  rotates, oil escapes the chain  340  and is diverted by baffle  315  an adjacent entrance of the reservoir system  329  oil also escapes the holes  353  and goes to the reservoir system  329 . A lubricant collective fluid receptacle  361  is formed by the housing  314  on a side  331  of the housing opposite a side exposed to the clutch housing  352 . A cover for the lubricant collection receptacle  361  is provided by a plate  333 . 
     An axial needle bearing  373  ( FIG. 12 ) is adjacent to thrust washers  375  and  377  which allow the housing to absorb the axial force caused by engagement of the clutch provided by the clutch housing  352  and the hub  362  into the primary shaft  316 . The housing has a passage  401 . The passage  401  has one end connected with the receptacle  361  forming a drain for the receptacle  361 . The passage  401  has an opposite end that is connected with a multi-diameter chamber  403 . Chamber  403  is connected with a passage  371  which is connected with a lubrication passage  381  which can deliver lubrication into a hub lubrication passage  383  which is axial which is intersected by hub radial passage  384  which can lubricate the friction pack  359  which is at the interface between the hub  362  and the clutch housing  352 . 
     The chamber  403  has a first section  407  that has placed therein a ball  409 . The first section  407  is fluidly connected with a passage  402 . Passage  402  fluidly communicates with a control volume that pressurizes clutch apply piston  374 . The chamber has a reduced section  411  that intersects an enlarged section  413 . Section  413  intersects with passage  371  and passage  401 . The chamber  403  is sealed by an end cap  421 . Slidably mounted within the chamber  403  is a piston valve  425 . The piston valve  425  has a bore  427  that mounts a coil spring  429 . The coil spring  429  pushes the piston valve  425  towards the ball  409  causing a head  431  of the piston valve  425  to seat against a valve seat  433 . An interior portion of the cap supports an extreme end of the coil spring  429 . The spring  429  urges the piston valve  425  towards the ball  409  causing the head  431  to seal on the valve seat  433  thereby cutting off fluid communication from the passage  401  and collection receptacle  361  to the hub lubrication passage  383 . Accordingly, under normal circumstances, the collection receptacle  361  will be fully filled, the overflow is then allowed to fall down to a sump of the transfer case. When the clutch  359  is engaged by the hydraulically powered piston  374 , fluid pressure will build up within passage  402  forcing the ball  409  against a  437  stem of the piston valve  425 . The above noted action will compress the spring  429  and dislodging the piston valve head  435  from the valve seat  433 . Lubricant is now allowed to gravitationally flow to lubricate the friction pack  359  whenever the clutch is engaged. 
       FIGS. 16 and 17  show an alternative fluid actuated valve  525 . Passage  501  directly connects to the receptacle  361  with chamber  503 . Spring loaded valve  525  has a diametric side  539  that meter valves a passage  571 . Passage  571  connects with passage  381 . A stem of valve  525  is moved by the ball  409  upon activation of the clutch piston  374  in a manner as previously described for the valve  425 . 
     The description of the invention is merely exemplary in nature and, thus, 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.