Abstract:
A two-speed segmented transfer case includes an automatic transmission side, and a transfer case side. The transfer case side having a gear reduction set, and a shift sleeve for selecting between the high, or direct drive speed, and the low, or reduced gear speed. The transmission side includes a hydraulic clutch which is used to transfer power from the transmission, to the front wheels. The hydraulic clutch is operated and controlled by the use of automatic transmission fluid that comes from the vehicle transmission. When fully engaged, the hydraulic clutch causes the power coming into the transfer case to be split between the front and rear wheels. This configuration allows for the elimination of a separate actuation system that would normally control the engagement of the clutch.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/578,943, filed Jun. 12, 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to two-speed transfer cases, more particularly, an apparatus for operating a two-speed transfer case through the use of hydraulic fluid from a vehicle transmission.  
       BACKGROUND OF THE INVENTION  
       [0003]     The vast majority of transfer cases in the United States are used in conjunction with automatic transmissions. Transfer cases frequently contain clutch packs and shifting elements. Historically, these clutches and shifting elements have been powered by electric motors, magnetic coils, solenoids, and hydraulic pistons getting their pressure from pumps which are a part of the transfer case assembly. The automatic transmission has available hydraulic pressure that has not previously been used to perform transfer case functions due to issues with lubrication complexity. The oil level of the transfer case portion of the powertrain must be kept at a different level than the level mandated by the automatic transmission. This has required the regulation of a return pump in the transfer case to give back the oil to the automatic transmission. The pressure also has had to be routed through complex housings or through long rotating shafts. This configuration is expensive to manufacture and the benefits have not outweighed the increase in cost to use the automatic transmission pump and valve body for control of the transfer case functions.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention is directed to a transfer case configuration that overcomes the above disadvantages. Accordingly, a first embodiment of the present invention is a transfer case having a segmented casing, including a first side in communication with a transmission and sump of transmission fluid. A second side of the transfer case is in communication with a transfer case sump. A drive shaft is positioned in the segmented casing and includes a drive end disposed in the first side of the casing for coupling with a transmission and an output end disposed in the second side of the casing. Circumscribed about the drive shaft is a sprocket shaft having a sprocket mounted thereon. The first embodiment also includes a hydraulic clutch positioned in the first side of the transfer case that is operably coupled between the drive shaft and the sprocket for transfer of rotation of the drive shaft to the sprocket.  
         [0005]     A second embodiment of the present invention is a transfer case for use in a motor vehicle having a casing made up of two segments. A first segment is in communication with a transmission fluid sump, and a second segment is in communication with a transfer case fluid sump. A planetary gearset is disposed in the second segment with the transfer case fluid, and connected to the primary output shaft of the transfer case. A shaft having a first end coupled to the transmission is disposed in the first segment, and has a second end disposed in the second segment, wherein the second end is coupled to the planetary gearset. A sprocket is mounted on a sprocket shaft that circumscribes and rotates about the shaft. A hydraulic clutch is disposed in the first segment of the casing which is operated by the use of hydraulic fluid from the transmission, and couples the sprocket shaft to the planetary gearset.  
         [0006]     In a third embodiment of the present invention, a method of actuating low to high shifts as well as engaging two-wheel and four-wheel drive modes in a transfer case using the fluid from an automatic transmission is described. The method includes separating a transfer case into two segments, a first segment in communication with a transmission and a sump of transmission fluid, and a second segment in communication with a transfer case side and a transfer case sump of fluid. A gear reduction set is also provided which is disposed in the second segment of the transfer case, driven by an input shaft, and in communication with a primary output shaft. Included in the third embodiment is a shift rail, mounted in the transfer case, which slides axially in the casing. A shift sleeve is operably disposed about the shift rail that is in communication with a bracket and the gear reduction set. A hydraulic clutch is disposed in the first segment of the transfer case, and a sprocket and sprocket tube assembly are in communication with the hydraulic clutch.  
         [0007]     The transfer case layout has the low range gear set on the output side of the sprocket and chain. The biasing clutch is placed in front of the sprocket and chain. The front portion of the transfer case housing which separates the fluids of the automatic transmission and the transfer case is in a location between the biasing clutch and the sprocket and chain. This allows the biasing clutch to reside within the same lube environment as the automatic transmission. It also allows the shift force required to be generated hydraulically also in the front portion of the transfer case. All leakage and return oil from these functions will be kept within the automatic transmission sump and thereby eliminate the need for a return pump. The configuration shown in the drawings is an “on demand” type of transfer case. However, this principle is not limited to an on demand transfer case. It could be used with a differentiated all wheel drive transfer case. Although the present invention can be used to shift a two-speed transfer case, it is obvious that it is not limited to a two-speed transfer case. A single speed transfer case would be a far less complex assembly and may be much more economical than the traditional single speed configurations.  
         [0008]     A hydraulic clutch is provided for shifting of the transfer case in the two-speed transfer case embodiment, it is usually smoother and easier to achieve precise control than electromotive actuated clutches. However, other types of clutch actuation can be utilized in the present invention.  
         [0009]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0011]      FIG. 1  is a sectional view of a transfer case in accordance with the present invention.  
         [0012]      FIG. 2  is a sectional view of an alternative single-speed embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     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.  
         [0014]     Referring now to  FIG. 1 , a transfer case of the present invention is generally shown at  10 . Transfer case  10  includes a segmented casing  12  comprising a transmission side  14  and a transfer case side  24 . The transmission side  14 , which includes a transmission sump side  16  in communication with a transmission  18 . A wall  20  separates the transmission sump side  16  from the transfer case side  24 . The transfer case side  24  includes a transfer case sump  22 . Within the transmission side  14 , there is a hydraulic clutch  26  that is in communication with the input shaft  28  that is connected to the transmission  18  through the use of a gear reduction set  32 . The hydraulic clutch  26  is comprised of clutch hub  34 , clutch housing  35 , apply piston  43 , pressure plate spring  45 , reaction plate  47 , and a series of separator plates  37  interleaved with a series of friction plates  41 . The friction plates  41  are splined at their inner diameter to clutch hub  34 , and the separator plates are splined at their outer diameter to clutch housing  35 . The hydraulic clutch  26  is engaged and released through the use of fluid pressure from a transmission pump (not shown). This allows for the hydraulic controls in the transmission  18  to also control the hydraulic clutch  26  in the transfer case  10 .  
         [0015]     Set forth in  FIG. 1  is a 2-speed embodiment of the transfer case  10  of the present invention. Transfer case  10  includes an input shaft  28  coupled with a reduction gear set  32 . The input shaft  28  is splined to the sun gear  42 . The sun gear  42  is in communication with the planetary gears  44 , which are also in communication with the ring gear  46 . The planetary gears  44  are mounted on shafts  49  and are free to rotate thereon. The shafts  49  are connected to carrier  50 , thereby providing a connection between the planetary gears  44  and the carrier  50 . On the outside of the ring gear  46 , there is a shift sleeve  48 , which can slide forward and rotationally secure the ring gear  46  to the carrier  50 , allowing the reduction gear set  32  to rotate together, and give a one-to-one or direct ratio between the input shaft  28  and front output shaft  54  and the rear output shaft  52 . The rear output shaft  52  includes a primary propshaft  78  connected to a driveshaft (not shown), which is used for driving a first set of wheels. The output shaft  54  has a secondary propshaft  80 , connected to a driveshaft (not shown), which is used to drive a second set of wheels.  
         [0016]     When the shift sleeve  48  is in the position shown in  FIG. 1 , the reduction gear set  32  is in neutral, and the front output shaft  54  and rear output shaft  52  can rotate independently from each other. If the shift sleeve  48  is slid rearward, the ring gear  46  will be secured to the segmented casing  12 , and the carrier  50  will rotate at a predetermined speed, that is a function of the sun gear  42  speed (between 2.5 and 3.0 to 1.0). A shift fork  58  connects the shift rail  56  longitudinally to the shift sleeve  48 . The translation of the shift sleeve  48  is accomplished by sliding the shift rail  56 . The shift rail  56  is moved by hydraulic pressure (coming from the pump of transmission  18 ) on the end of the round cross-section  60 . The hydraulic pressure is fed through channel  59  and applies pressure to the round cross-section  60 . The default position for the shift rail  56  is the direct-drive position (in which the shift rail  56  is positioned all the way to the left). The shift rail  56  is held in the default position and biased in that direction by a return spring  62 . Hydraulic pressure is applied to the end of the shift rail  56  opposite the return spring  62  for shifting the gear reduction set  32 . The shift rail  56  is held in the neutral position by way of a solenoid  64  that, once engaged, inserts a pin  66  into a slot  68  on the shift rail  56 , only allowing the shift rail  56  to slide to a position such that the shift sleeve  48  is in a position such that the ring gear  46  is not engaged to the carrier  50  or the segmented casing  12 .  
         [0017]     The carrier  50  is permanently splined to the rear output shaft  52  on a first side, on a second side the carrier  50  is splined to the torque tube  40 . The torque tube  40  extends forward, through the sprocket  30 , to the hydraulic clutch  26 . The hydraulic clutch  26  frictionally connects the torque tube  40  to the sprocket shaft  70  that returns torque to the sprocket  30 . The sole driving torque to the sprocket  30  is delivered by the hydraulic clutch  26 . This can be modulated by regulating the hydraulic apply pressure. Hydraulic supply pressure comes from the transmission  18 , preferably a transmission oil pump is used for the source of the hydraulic pressure.  
         [0018]     In  FIG. 1 , when the use of four-wheel drive or all wheel drive is not necessary, the hydraulic clutch  26  is not engaged. The pressure plate spring  45  biases the apply piston  43  away from the friction plates  41  and separator plates  37 . When engagement of the four-wheel or all-wheel drive capabilities of the vehicle become necessary, the hydraulic apply pressure is delivered through the hollow bore  33  in the center of the input shaft  28  and outwardly through a radial bore  36 , and then through a radial drilled hole  38  in the intermediate torque tube  40  into the pressure chamber  72 . The hydraulic clutch seals  39  only allow transmission fluid to be transferred into the pressure chamber  72 , and do not allow any of the transmission fluid to leak into any other parts of the transfer case  10 . As transmission fluid fills pressure chamber  72 , the pressure applied to the apply piston  43  is greater than the force exerted by the pressure plate spring  45 , and the apply piston  43  is forced toward the friction plates  41  and separator plates  37 , causing the friction plates  41  to frictionally engage the separator plates  37  and achieve the same speed.  
         [0019]     Once the hydraulic clutch  26  is fully engaged, torque is transferred from the input shaft  28  through the gear reduction set  32 , either at a one-to-one or reduced gear ratio, through torque tube  40 , to the clutch hub  34 , through the engaged friction plates  41  and separator plates  37 , through the housing  35 , through the sprocket shaft  70 , and to the sprocket  30 . The driven sprocket  30 , transfers driving torque by means of the chain  76  to the front output sprocket  74  that is splined to the front output shaft  54 . As will be readily appreciated by those skilled in the art, gears could be used, instead of the sprockets, in a conventional manner.  
         [0020]     It should also be noted that driving the primary propshaft  78  and secondary propshaft  80  through splined engagements to either side of the carrier  50  can result in drive train windup through the transfer case. This is avoided in this assembly by the simple relief of pressure in the hydraulic clutch  26 .  
         [0021]     It should also be noted that the hydraulic clutch  26  may be partially engaged so as to provide only a partial torque transfer to the secondary propshaft  80 . Partially engaging the hydraulic clutch  26  may be more beneficial for certain driving conditions than full engagement.  
         [0022]     An alternate embodiment of the present invention is a single-speed transfer case design. This single-speed embodiment is generally shown at  110  in  FIG. 2 , wherein like numbers differing by 100 refer to like elements. Transfer case  110  operates in a similar fashion as the two-speed design, but it does not incorporate the use of the gear reduction set  32  in conjunction with the separate input shaft  28  and output shaft  52 . In this embodiment, there is a single input shaft  82  that runs through the transfer case  110 , and includes a driven end portion  83  and a drive end portion  85 . The hydraulic clutch  126  operates in similar fashion as the two-speed design; the hydraulic fluid is delivered through the bore  84  of the input shaft  82 , but does not need to be fed through the intermediate torque tube  40  as in the two-speed design. In this design, there is no intermediate torque tube  40 , such as the one connecting the gear reduction set  32  to the hydraulic clutch  26  in the two-speed design. However, there is a connection shaft  86  that connects the hydraulic clutch  126  to the drive sprocket  130 . When the hydraulic clutch  126  is engaged, torque is not only transferred through the input shaft  82 , but is also transferred through the connection shaft  86  to the drive sprocket  130 , the drive sprocket  130  in turn communicates torque through the chain  176  to the driven sprocket  174 , delivering torque to the front propshaft  180 .  
         [0023]     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.