Abstract:
A transfer case for use with four-wheel drive vehicles incorporates a pass-through power takeoff shaft to drive remote secondary implements or accessory devices. The power takeoff shaft delivers rotational power from the vehicle transmission to the remote implement or accessory by passing through the housing of the transfer case to improve ground clearance and minimize driveline angles. The housing for the transfer case can mount bearings that rotatably support the power takeoff shaft. Alternatively, a tubular member can be mounted in the transfer case to provide a passageway through which the power takeoff shaft can pass through the transfer case. The points of engagement of the power takeoff shaft and the transfer case housing are sealed to prevent the loss of lubricating fluid from the transfer case. In each embodiment, the power takeoff shaft passes through the transfer case without engagement of or interference with the drive components therein.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation in part of U.S. patent application Ser. No. 13/398,055, filed on Feb. 16, 2012, now abandoned, the content of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to a transfer case for a four wheel drive vehicle, and more particularly, to a transfer case having a power takeoff shaft extending through the transfer case without operatively engaging the drive components within the transfer case. 
       BACKGROUND OF THE INVENTION 
       [0003]    A transfer case is a part of a drive system for four wheel drive and all-wheel drive vehicles. The transfer case houses drive components that connect to the primary drive mechanism of the vehicle and transfers operative power to the front drive axle via a drive shaft associated with the drive components within the transfer case. Operative power is generally transferred from the primary drive mechanism to the drive components within the transfer case using a set of gears or a chain drive mechanism. 
         [0004]    On some vehicles, including particularly commercial trucks and tractors, a power takeoff mechanism (PTO) is provided to transfer engine power to another piece of equipment or an accessory device carried by the vehicle. Typically, the power takeoff mechanism transfers engine power from the transmission to a secondary implement or accessory device by a power takeoff shaft. The power takeoff mechanism is operable independently of the transfer of engine power through the transfer case. Typically, manual drive transmissions have provisions for connecting the power takeoff mechanism lower on the transmission, in which case the power takeoff shaft is more easily able to pass below the transfer case to deliver engine power to the remote secondary or accessory device. Customarily, automatic transmissions provide operative connection of the power takeoff mechanism to the side of the transmission. As a result, power takeoff shafts are usually provided with universal joints to enable the power takeoff shaft to circumvent the transfer case to deliver operative power to the secondary implement or accessory device located behind the transfer case, as is depicted in  FIG. 2  in broken lines. 
         [0005]    The routing of the power takeoff shaft below the transfer case creates clearance problems, as the power takeoff mechanism often become the lowest part of the drive mechanism. Furthermore, maintaining acceptable driveline angles within the universal joints can be problematic, as designing a power takeoff mechanism that will maximize ground clearance while minimizing the number of universal joints and the driveline angles required of the universal joints can prove to be difficult. 
         [0006]    It would be desirable to provide a drive mechanism for a four wheel drive vehicle utilizing a transfer case that would allow for providing a power takeoff mechanism that would maximize ground clearance while minimizing problems with universal joints in the power takeoff shaft. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of this invention to overcome the disadvantages of the prior art by providing a transfer case that has a pass-through power takeoff shaft. 
         [0008]    It is another object of this invention to provide a transfer case for use with a four wheel drive vehicle that allows the power takeoff shaft to pass through the transfer case without interfering with the drive components within the transfer case. 
         [0009]    It is a feature of this invention that the power takeoff shaft can pass through the housing of the transfer case to connect with a secondary implement or an accessory device located behind the transfer case. 
         [0010]    It is an advantage of this invention that the positioning of the power takeoff shaft does not define the minimum ground clearance for the vehicle. 
         [0011]    It is another feature of this invention that the power takeoff shaft passes through the transfer case housing without engaging or interfering with the drive components within the transfer case. 
         [0012]    It is another advantage of this invention that the positioning of the power takeoff shaft through the transfer case minimizes the number of universal joints required for operation of the power takeoff mechanism. 
         [0013]    It is still another advantage of this invention that the positioning of the power takeoff shaft through the transfer case minimizes the driveline angles for the universal joints incorporated into the power takeoff shaft. 
         [0014]    It is still another feature of this invention that the power takeoff shaft can incorporate a tubular member defining a passageway through the housing of the transfer case to provide an isolated passageway for the pass-through power takeoff shaft. 
         [0015]    It is yet another feature of this invention that the entrance and exit of the power takeoff shaft through the housing of the transfer case is sealed to prevent the loss of lubricating fluid for the drive components within the transfer case. 
         [0016]    It is yet another advantage of this invention that the passage of the power takeoff shaft through the transfer case does not disrupt the operation of the drive components within the transfer case. 
         [0017]    It is a further feature of this invention that the housing of the transfer case can be utilized to support a bearing or bearings for rotatably supporting the power takeoff shaft. 
         [0018]    It is still another object of this invention to provide a transfer case accommodating a pass through power takeoff shaft which is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use. 
         [0019]    These and other objects, features and advantages are accomplished according to the instant invention by providing a transfer case for use with four-wheel drive vehicles that incorporates a pass-through power takeoff shaft to drive remote secondary implements or accessory devices. The power takeoff shaft delivers rotational power from the vehicle transmission to the remote implement or accessory by passing through the housing of the transfer case to improve ground clearance and minimize driveline angles. The housing for the transfer case can mount bearings that rotatably support the power takeoff shaft. Alternatively, a tubular member can be mounted in the transfer case to provide a passageway through which the power takeoff shaft can pass through the transfer case. The points of engagement of the power takeoff shaft and the transfer case housing are sealed to prevent the loss of lubricating fluid from the transfer case. In each embodiment, the power takeoff shaft passes through the transfer case without engagement of or interference with the drive components therein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The foregoing and other objects, features, and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description that follows, in conjunction with the accompanying sheets of drawings. It is to be expressly understood, however, that the drawings are for illustrative purposes and are not to be construed as defining the limits of the invention. 
           [0021]      FIG. 1  is a perspective view of a portion of the drive mechanism for a four wheel drive vehicle utilizing a transfer case coupled to the primary drive mechanism and having a power takeoff mechanism incorporating the principles of the instant invention; 
           [0022]      FIG. 2  is a side view of the primary drive mechanism as shown in  FIG. 1 , but with the front axle drive shaft being removed for purposes of clarity, and having a transfer case incorporating the principles of the instant invention, the prior art positioning of the power takeoff shaft being shown in broken lines passing below the transfer case; 
           [0023]      FIG. 3  is a perspective view of a front housing member of the transfer case; 
           [0024]      FIG. 4  is a perspective view of a rear housing member of the transfer case; 
           [0025]      FIG. 5  is a cross-sectional view taking along lines  5 - 5  of  FIG. 1  to show a portion of the transfer case as depicted in  FIG. 1  and a first embodiment of the mounting of the power takeoff shaft passing through the transfer case; 
           [0026]      FIG. 6  is an exploded rear perspective view of a rear portion of the transfer case showing a rear bearing assembly mounted on the transfer case housing for rotatably supporting the power takeoff shaft passing therethrough; 
           [0027]      FIG. 7  is a cross-sectional view of the transfer case taken along lines  7 - 7  of  FIG. 2  to show the passage of the power takeoff shaft without engagement or interference with the drive components within the transfer case; 
           [0028]      FIG. 8  is a rear perspective view of the transfer case showing an adapter for mounting a secondary implement or accessory directly to the transfer case while being powered by the power takeoff shaft passing through the transfer case; 
           [0029]      FIG. 9  is a perspective view of another embodiment of the transfer case accommodating the passage of the power takeoff shaft according to the principles of the instant invention; 
           [0030]      FIG. 10  is a cross-sectional view of a portion of the transfer case taken along lines  10 - 10  in  FIG. 9  to depict the mounting of the tubular member and the passage of the power takeoff shaft therethrough without engagement or interference with the drive components within the transfer case; 
           [0031]      FIG. 11  is a perspective view of yet another embodiment of the transfer case accommodating the passage of the power takeoff shaft according to the principles of the instant invention; 
           [0032]      FIG. 12  is a cross-sectional view of a portion of the transfer case taken along lines  12 - 12  in  FIG. 11 ; and 
           [0033]      FIG. 13  is a schematic perspective view of a four wheel drive vehicle having the drive mechanism incorporating the principles of the instant invention installed therein to drive the front and rear axles of the vehicle. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0034]    Referring to  FIGS. 1, 2 and 13 , a significant portion of the primary drive line  10  for a four wheel drive vehicle can best be seen. The vehicle  5  has a front axle  6  and a rear axle  7  which are both driven through the primary drive line  10 , as will be described in greater detail below. The vehicle  5  has a conventional motor (not shown) that provides a source of rotational power that is delivered to the transmission  12  by connection to the power input shaft  13  for the transmission  12 . As one skilled in the art will recognize, the transmission  12  is operable to vary the speed of rotation of the transmission output shaft  14  with respect to the speed of operation of the transmission input shaft  13 . The output shaft (not shown) of the motor, which is connected to the transmission  12  through the power input shaft  13 , through the transmission output shaft  14  which is conventionally connected to the rear axle drive shaft  15  is defined as the primary or main drive line  10 . 
         [0035]    The rear axle  7  of the vehicle  5  is driven directly from the transmission output shaft  14 , which becomes the rear axle drive shaft  15  via connection through a universal joint  15   a . The front axle  6  of the vehicle  5  is driven through a power transfer mechanism  25  associated with a transfer case  20 , as will be described in greater detail below, to transfer rotational power to a front axle drive shaft  16  which ultimately connects to the front axle  6  typically through a clutch (not shown) that permits selective operative engagement of the front axle drive shaft  16  with the front axle  6 . Many four wheel drive vehicles  5 , particularly commercial trucks and tractors, are also provided with a power takeoff mechanism  30  that is operable, as will also be described in greater detail below, to provide a source of operative power for a secondary implement or accessory device (not shown) that is associated with the vehicle  5 . This invention is directed to providing a drive system for a four wheel drive vehicle that delivers rotational power to both the front and rear axles  6 ,  7  of the vehicle  5  while providing a unique arrangement for the support of a power takeoff mechanism  30 . 
         [0036]    The transfer case  20  is best seen in  FIGS. 1-8 . The transfer case  20  includes a housing  21  that is generally oval in shape and is oriented perpendicularly to the drive line  10  rearwardly of the transmission  12 . The housing  21  is preferably manufactured from formed sheet metal or castings into mating front and rear housing members  22 ,  23  that are joined together by a plurality of fasteners  24  spaced around the periphery of the housing  21  with a seal (not shown) therebetween to form a fluid tight hollow housing  21  that retains lubricating fluid for the power transfer mechanism  25  housed within the housing  21 . As best seen in  FIGS. 3 and 4 , the housing  21  is formed to include a housing extension  19  that connected to the transmission  12  to become part of the drive line  10 . 
         [0037]    The power transfer mechanism  25  within the transfer case  20  is best seen in  FIG. 7  and includes a drive sprocket  26  mounted on the transmission output shaft  14  to be rotatable therewith. The front axle drive shaft  16  is rotatably supported by bearings  17  mounted internally of the housing  21  at the distal end of the transfer case  20  from the transmission output shaft  14  and has a driven sprocket  27  mounted thereon to be rotatable therewith. An endless chain coupler  29  is entrained around the drive sprocket  26  and the driven sprocket  27  to transfer rotational power from the transmission output shaft  14  to the front axle drive shaft  16 . One skilled in the art will recognize that the power transfer mechanism  25 , including the sprockets  26 ,  27  and the chain coupler  29 , is the preferred embodiment of the power transfer mechanism  25 , but is not the only embodiment that would be operable to transfer rotational power to the front axle. For example, a series of intermeshing gears (not shown) could interconnect the transmission output shaft  14  and the front axle drive shaft  16  to transfer rotational power. A belt drive arrangement (not shown) would also be an operable embodiment. 
         [0038]    The power takeoff mechanism  30  is operatively coupled to the front portion of the transmission to be engaged with the transmission input shaft  13  so as to receive rotational power from the engine or motor (not shown) without modification induced by the operation of the transmission  12 . One of ordinary skill in the art will recognize that the power takeoff mechanism (also known as the PTO)  30  receives rotational power from the input shaft  13  through a drive transfer mechanism  32  that causes the power takeoff shaft  35  to rotate. As shown in broken lines in  FIG. 2 , the power takeoff shaft (also known as the PTO shaft)  35  conventionally included multiple universal joints  33  that enabled the PTO shaft  35  to bend from the drive transfer mechanism  32  to pass below the transfer case  20  in order to reach a position behind the transfer case to power a secondary implement or accessory device (not shown). 
         [0039]    According to the principles of the instant invention, instead of the PTO shaft  35  passing below the transfer case  20 , the transfer case  20  is adapted to receive the PTO shaft  35  and allow the PTO shaft  35  to pass through the transfer case  20  without engagement with or interference with the power transfer mechanism  25  housed within the housing  21 . Since the transfer case  20  needs to be a fluid-tight structure to keep the power transfer mechanism  25  therein lubricated, the entrance and exit of the PTO shaft  35  through the housing  21  of the transfer case  20  will require sealing as well as proper placement so as to not interfere with the operation of the power transfer mechanism  25 . 
         [0040]    Referring now to  FIGS. 1-7 and 13 , the structure of the power takeoff mechanism  30  passing through the transfer case  20  can best be seen. Rather than pass below the transfer case  20 , as is shown in broken lines in  FIG. 2 , the power takeoff shaft  35  is aligned with the transfer case  20 . A first PTO opening  22   a  is formed in the front housing member  22  of the housing  21 , while a second PTO opening  23   a  is formed in the rear housing member  23  of the housing  21  in alignment with the first PTO opening  22   a  to allow for the passage of the PTO shaft  35  through the transfer case  20 . To rotatably support the PTO shaft  35  through the transfer case  20 , a bearing  36  is supported in the first PTO opening  22   a  by a collar  34  welded and sealed to the front housing member  22  of the housing  21  to maintain the transfer case  20  as a fluid tight structure. Similarly, a second bearing  37  is mounted at the second PTO opening  23   a  by a rear collar  34   a  welded and sealed with the rear housing member  23  of the housing  21 . With the PTO shaft  35  mounted for rotation by the bearings  36 ,  37 , the PTO shaft  35  is free to operate while the transfer case  20  is maintained as a fluid tight structure. 
         [0041]    As is best seen in  FIG. 7 , the selection of the location for the PTO openings  22   a ,  23   a , is such as to allow the PTO shaft  35  to pass through the void in the power transfer mechanism  25  between the sprockets  26 ,  27  and between the upper and lower runs of the chain coupler  29 . Furthermore, the location of the PTO openings  22   a ,  23   a  is generally aligned with the drive transfer mechanism  32  so as to present a substantially linear path for the positioning of the PTO shaft  35 . As best seen in  FIG. 7 , the preferably configuration for the location of the PTO shaft through the transfer case  20  is closer to the front axle drive shaft  16  than the primary drive line  10  such that with the distance from the transmission output shaft  14  to the front axle drive shaft  16  being x 3 , the distance x 1  from the front axle drive shaft  16  to the PTO shaft  35  is smaller than the distance x 2  from the PTO shaft  35  to the transmission output shaft  14 . In such a linear configuration, the PTO shaft  35  could potentially utilize fewer universal joints  33 . Furthermore, one skilled in the art will recognize that the PTO shaft  35  between the two bearings  36 ,  37  is exposed to lubrication from the lubricating fluid (not shown) placed internally of the transfer case  20  to lubricate the power transfer mechanism  25 ; however, such exposure is not detrimental to the operation of the power takeoff mechanism  30 , nor detrimental to the operation of the power transfer mechanism  25 . 
         [0042]    As is depicted in  FIGS. 1, 2 and 13 , the PTO shaft  35  can extend rearwardly of the transfer case  20  to power the operation of a secondary device or accessory  38  positioned remotely from the transfer case  20 . Such extension of the PTO shaft  35  will typically require the utilization of at least one universal joint  33 . On the other hand, some configurations of the secondary device or accessory, such as a hydraulic pump  38   a  as depicted in  FIG. 8 , can be mounted directed to the rear housing member  23  of the housing  21  through a mounting bracket  39  that is affixed, such as by welding, to the rear collar  34   a  secured to the housing  21  and configured to mate with the device  38   a  mounted thereto. In such a configuration, the distal end of the PTO shaft  35  is configured to mate with the input shaft of the device  38   a  in order to transfer rotational power thereto. Accordingly, a hydraulic pump  38   a  can be mounted on the rear housing member  23  of the housing  21  and be driven directly by the PTO shaft  35 . The operation of the hydraulic pump  38   a  can drive the operation of a number of remote hydraulic devices (not shown). 
         [0043]    An alternative structural configuration for passing the PTO shaft  35  through the interior of the transfer case  20  can be seen in  FIGS. 9 and 10 . Rather than have a pair of bearings  36 ,  36  mounted on the housing  21  to rotatably support the operation of the PTO shaft  35 , the transfer case  20  can be provided with a receiving tube  40  passing through the front and rear PTO openings  22   a ,  23   a  and being formed with at least one external circular flange  42  to facilitate affixing, such as by welding, the receiving tube  40  to the front and rear housing members  22 ,  23  of the transfer case housing  21 . With the receiving tube  40  sealed to the housing  21 , such as by the welding of the receiving tube  40  to the housing  21 , the transfer case  20  remains fluid tight and is thus formed with a passageway extending through the transfer case  20 . 
         [0044]    The PTO shaft  35  can then be passed through the transfer case  20  by being positioned through the passageway defined by the receiving tube  40 . Preferably, bearings  46 ,  47  are mounted in the opposing front and rear ends of the receiving tube  40  to rotatably support the operation of the PTO shaft  35 . The bearings  46 ,  47  in the receiving tube  40  do not require sealing to maintain the fluid tight integrity of the transfer case  20 , as the receiving tube  40  seals the openings  22   a ,  23   a . In this configuration, the central, exterior portion of the receiving tube  40  is exposed to the lubrication within the transfer case  20 , rather than the PTO shaft  35  itself. The mounting of the bearings in the receiving tube  40  has the advantage of being easier to replace in the event of bearing failure, as the bearings  46 ,  47  in the receiving tube  40  would not require re-sealing as the bearings  36 ,  37  would require with respect to the housing  21 . 
         [0045]    Yet another alternative structural configuration of the power takeoff shaft  35  passing through the transfer case  20  can be seen in  FIGS. 11 and 12 . In this configuration, the forward portion of the PTO shaft  35  between the drive transfer mechanism  32  and the transfer case  20  is devoid of universal joints. The PTO shaft  35  is supported by the internal bearings (not shown) of the drive transfer mechanism  32  and the single bearing  47  at the rearward side of the receiving tube  40 . A universal joint  33  located rearwardly of the transfer case  20  will enable the PTO shaft  35  to bend slightly to accommodate the positioning of the secondary implement or accessory. As with the other embodiments of the PTO mechanism  30  described above, the PTO shaft  35  passes through the transfer case  20  without disrupting the operation of the drive mechanism  25  within the housing  21 . The receiving tube  40  will seal the front side  22  of the housing  21 , while the receiving tube  40  or the bearing  47  will seal the rear side  23  of the housing  21  to maintain the fluid tight integrity of the transfer case  20 . 
         [0046]    It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention.