Patent Publication Number: US-2007117672-A1

Title: Tandem axle system

Description:
FIELD OF THE INVENTION  
      The present invention relates to a tandem axle system for vehicles. More specifically, the present invention relates to a tandem axle system utilizing hub reduction gearing.  
     BACKGROUND OF THE INVENTION  
      Known tandem axle systems for vehicles suffer from several disadvantages. First, the known systems typically have input shafts of the forward drive axle system located in a relatively high position to connect with the drive shaft from the prime mover of the vehicle. This relatively high position results in a tall forward drive axle system housing that takes up space among the frame members of the vehicle.  
      Second, the known systems utilize a drive shaft to transfer drive from the forward drive axle system to the rear drive axle system. The end of the drive shaft connected to the input shaft of the rear drive axle system must typically be lowered and laterally offset from the end of the drive shaft connected to the output shaft of the forward drive axle system. Those skilled in the art know that it is undesirable to unnecessarily lower and laterally offset the drive shaft as it may result in increased vibration and it may increase the wear on the joints between the drive shaft and the rear drive axle system and the forward drive axle system.  
      Third, some prior art systems use a spiral bevel pinion in both the forward drive axle system and the rear drive axle system. In the forward drive axle system, sufficient distance must be provided between the spiral bevel pinion and the output shaft, thus contributing to the overall height of the forward drive axle system.  
      In light of the disadvantages of known tandem axle systems, it would be desirable to have a forward drive axle system with a relatively small height, a drive shaft with a relatively small down angle and a relatively small lateral offset between the forward drive axle system and the rear drive axle system and a forward drive axle system housing and a rear drive axle system housing that provide the greatest ground clearance.  
     SUMMARY OF THE INVENTION  
      The present invention is directed toward a tandem axle system having a forward drive axle system connected to a rear drive axle system via a drive shaft. The forward drive axle system has a hypoid bevel pinion driving a forward ring gear. The forward ring gear drives a first forward half shaft and a second forward half shaft via a forward differential. The rear drive axle system utilizes a spiral bevel pinion to drive a rear ring gear. The rear ring gear drives a first rear half shaft and a second rear half shaft via a rear differential. A separate hub reduction system is located on the opposite end of each of the half shafts from the forward differential and the rear differential. Each hub reduction system comprises a sun gear for engagement with the half shaft. The sun gear is in driving engagement with a plurality of planetary gears within a planet carrier. The planet carrier drives a wheel hub. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above, as well as other advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which:  
       FIG. 1  is a schematic side view of the present invention;  
       FIG. 2  is a schematic top view of the present invention;  
       FIG. 3  is a cut-away schematic side view of a component of the invention;  
       FIG. 4  is a partial, schematic cut-away top view of the component depicted in  FIG. 3 ;  
       FIG. 5  is a cut-away schematic side view of another component of the invention;  
       FIG. 6  is a partial, cut-away schematic top view of the component depicted in  FIG. 5 ; and  
       FIG. 7  is a cut-away schematic side view of yet another component of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions, directions or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless the claims expressly state otherwise.  
      Referring now to  FIG. 1 , a forward drive axle system  10  and a rear drive axle system  12  for a vehicle, such as a truck, are depicted in a tandem arrangement. The forward drive axle system  10  and the rear drive axle system  12  are connected by a drive shaft  14 . A portion of an input shaft  16  of the forward drive axle system  10  is depicted. The input shaft  16  is connected via a yoke (not shown) to a prime mover drive shaft (not shown). The prime mover drive shaft is connected to a prime mover (not shown), such as an internal combustion engine, to provide rotational drive to the prime mover drive shaft, as known by those skilled in the art. The input shaft  16 , connected via the yoke to the prime mover drive shaft, thus rotates with the prime mover drive shaft.  
      The forward drive axle system  10  also comprises a housing  18 . The housing  18  may be of one-piece construction or multi-piece construction. The components within the housing  18  will be described in greater detail below. Suffice it to say at this point that drive is transmitted through the forward drive axle system  10  to an output shaft  20 , which is partially shown in  FIG. 1 . The output shaft  20  of the forward drive axle system  10  is connected via a yoke (not shown) to one end of the drive shaft  14 . The output shaft  20  provides rotational drive to the drive shaft  14 .  
      The other end of the drive shaft  14  is connected to an input shaft  22 , partially depicted in  FIG. 1 , of the rear drive axle system  12 . The rear drive axle system  12  also comprises a housing  24 . The housing  24  may be of a one-piece construction or multi-piece construction. The components located within the housing  24  will be described in greater detail below.  
      Based on  FIG. 1 , it can be appreciated that the drive shaft  14  angles downwardly at an angle  26  from the output shaft  20  of the forward drive axle system  10  to the input shaft  22  of the rear drive axle system  12 .  
      Turning now to  FIG. 2 , the tandem nature of the forward drive axle system  10  and the rear drive axle system  12  can also be appreciated. It can also be seen that a first forward half shaft housing  28  and a second forward half shaft housing  30  extend away from the housing  18  of the forward drive axle system  10 . A first rear half shaft housing  32  and a second rear half shaft housing  34  also extend away from the housing  24  of the rear drive axle system  12 . About the end portions  36  of each half shaft housing  28 ,  30 ,  32 ,  34  there is located a hub  38  and a wheel  40  where the wheel  40  is secured to the hub  38  with a plurality of mechanical fasteners, such as bolts and nuts. Tires  42  are mounted to each wheel  40  in a manner known to those skilled in the art.  
      The drive shaft  14  connecting the forward drive axle system  10  and the rear drive axle system  12  can also be seen in  FIG. 2 . It can be appreciated that the drive shaft  14  has a small lateral offset  44  from its connection at one end to the output shaft  20  of the forward drive axle system  10  and the input shaft  22  of the rear drive axle system  12 .  
       FIG. 3  provides a cut-away side view of the forward drive axle system  10 . The input shaft  16  is mounted for rotation within the housing  18  on at least one input bearing  46 . An interaxle differential  48  is mounted on the input shaft  16  for rotation therewith. The interaxle differential  48  divides the rotational drive from the input shaft  16  between a first helical gear  50  and a side gear  52 .  
      The first helical gear  50  drives a second helical gear  54  located beneath the first helical gear  50 . The second helical gear  54  is mounted on a forward pinion shaft  56 . The forward pinion shaft  56  is mounted for rotation within the housing  18  on at least two bearings  58 . A hypoid bevel pinion  60  is located on the end of the forward pinion shaft  56 . The hypoid bevel pinion  60  is drivingly connected to a forward ring gear  62 A.  
      A hypoid bevel pinion  60  is preferably used in the forward drive axle system  10  because, with its lower position on the forward ring gear  62 , it does not interfere with the input shaft  16  as a spiral bevel pinion would. The hypoid bevel pinion  60  thus permits the input shaft  16  to be mounted lower in the forward drive axle system housing  18 , thus resulting in a vertically compressed forward drive axle system  10  compared to the prior art designs.  
      As shown in  FIG. 4 , the forward ring gear  62 A is fixed to a forward differential  64 , also within the housing  18 . The forward differential  64  divides rotational drive from the ring gear  62  to a first forward half shaft  66  and a second forward half shaft  68 .  
      The position of another ring gear  62 B is depicted in  FIG. 4 . Thus, it can be appreciated that forward gear sets, comprising the ring gear and the pinion gear, can be of various sizes without departing from the scope of the present invention. Although not shown in  FIG. 3  or  4 , it should be appreciated that the pinion  60  can be of a size other than as shown.  
      Referring back now to  FIG. 3 , it can be seen that the side gear  52  is connected to the output shaft  20  to provide drive to the drive shaft  14 . The output shaft  20  is mounted for rotation in the housing  18  with at least two bearings  70 , with three bearings being shown in  FIG. 3 . It can be appreciated, based on  FIGS. 3 and 4 , that the first and second forward half shafts  66 ,  68  are located below the output shaft  20 . It can also be seen that the hypoid bevel pinion  60  is located below the input shaft  16  and the output shaft  20  in the forward drive axle system  10 .  
      A cut-away side view of the rear drive axle system  12  in  FIG. 5  schematically depicts certain components thereof. Specifically, the input shaft  22  can be seen rotatingly mounted within the housing  24  on at least two bearings  74 . A spiral bevel pinion  76 A is located on the end of the input shaft  22 . The spiral bevel pinion  76 A is co-axial with the input shaft  22 .  
      The spiral bevel pinion  76 A is engaged with a rear ring gear  78 A. It can be appreciated that the spiral bevel pinion  76 A reduces the overall height required for the rear drive axle system housing  24  as compared to a hypoid bevel pinion. The rear ring gear  78 A is connected to a rear differential  80 , as shown in  FIG. 6 . The rear differential  80  divides the rotational drive provided by the ring gear  78 A between a first rear axle half shaft  82  and a second rear axle half shaft  84 .  
      The first and second forward axle half shafts  66 ,  68  and the first and second rear axle half shafts  82 ,  84 , each located within their respective half shaft housings  28 ,  30 ,  32 ,  34 , extend away from their respective differentials  64 ,  80 . The present discussion will now focus solely on a single axle half shaft and its interaction with a hub reduction system  87  for purposes of clarity and conciseness. It should be understood that in the preferred embodiment the following structures and components of the reduction system  87  are located at an outboard end portion  86  of each of the above described axle half shafts  66 ,  68 ,  82 ,  84 .  
      An axle half shaft, for example first forward axle half shaft represented by reference numeral  66 , has a plurality of teeth  88  located about its outboard end portion  86 , as seen in  FIG. 7 . A sun gear  90  is preferably directly engaged with the teeth  88  and thus rotates with the first forward axle half shaft  66 . A plurality of planetary gears  92  are located in a planet carrier  94  about the sun gear  90 . The number of planetary gears  92  may vary, however, in the presently described embodiment it is preferred that three planetary gears  92  are located in the planet carrier  94 . The planetary gears  92  are each preferably directly engaged with a set of teeth  96  of the sun gear  90 . As seen in  FIG. 7 , it is preferred that the planetary gears  92  be located directly radially outward from the sun gear  90 . Each planetary gear  92  is located on a shaft  98 . The shaft  98  is connected to the carrier  94  by a mechanical fastener.  
      Each planetary gear  92  is also engaged with an annulus gear  100 . The annulus gear  100  is prevented from rotating as it is secured to the housing  28  for the first forward axle half shaft  66 . A flange member  102  connects the annulus gear  100  with the housing  28  for the first forward axle half shaft  66 . It can be appreciated that the planet carrier  94  is thus forced to rotate by virtue of its interaction of the planetary gears  92 . The planet carrier  94  is attached to the wheel hub  38  by a member  104  extending over the annulus gear  100 . The member  104  urges the wheel hub  38 , and thus the tire  42 , or tires, attached to it, to rotate and move the vehicle the over the ground. Bearings  106  are located between the first forward axle half shaft housing  28  and the wheel hub  38  to permit the rotation.  
      The position of another pinion  76 B and another ring gear  78 B are depicted in  FIGS. 5 and 6 . Thus, it can be appreciated that rear gear sets, comprising the ring gear and the pinion gear, can be of various sizes without departing from the scope of the present invention.  
      In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiments. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.