Abstract:
The transfer case reduction gearset is often never used for its original intended function, that is, to provide an additional speed reduction (torque amplification) ratio for the powertrain. This concept allows for the increased use of the transfer case gearset components to work in concert with the automatic transmission to increase its ratio spread. This increase in ratio spread will result in improved launch performance for the vehicle by steepening the effective first gear ratio of the automatic transmission. The increase in ratio spread may also provide for reductions in numerical axle ratio of the vehicle thereby improving the fuel economy during normal highway operation. The present invention focuses on a method of shifting the transmission of the vehicle in accordance with the invention which includes providing a transmission connected to a vehicle engine having a predetermined number of gear ratios which are selectable.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/552,588, filed Mar. 12, 2004. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to improving the powertrain of a vehicle by providing additional speed reduction ratios.  
       BACKGROUND OF THE INVENTION  
       [0003]     Transfer cases are a common method of transferring power to more than one set of wheels in a motor vehicle. Devices such as transfer cases often have the ability to operate at more than one gear ratio. Typically a 1:1 gear ratio is used, and less often a reduced gear ratio, which can range from 1.5:1 to 4:1, is also used to generate more torque. For the transfer case to provide a transfer of power to more than one set of wheels in the vehicle, it is common practice for various types of synchronizers to be used to engage the gears in the transfer case providing the different gear ratios. These synchronizers can provide a smooth power transition with minimal effort.  
         [0004]     Because typical driving conditions do not mandate the use of the reduced speed, high-torque gearset in the transfer case, most owners of vehicle equipped with four-wheel-drive do not ever use this function of the transfer case.  
       SUMMARY OF THE INVENTION  
       [0005]     The transfer case reduction gearset is often never used for its original intended function, that is, to provide an additional speed reduction (torque amplification) ratio for the powertrain. This concept allows for the increased use of the transfer case gearset components to work in concert with the automatic transmission to increase its ratio spread. This increase in ratio spread will result in improved launch performance for the vehicle by steepening the effective first gear ratio of the automatic transmission, and will also allow for the vehicle to operate at a lower speed with the engine in a normal speed range. When the vehicle is traveling on a steep, downhill grade, there is a significant risk of overheating the brakes while trying to maintain a slow, safe speed without the assistance of a low range gear. The elevated ratio of engine speed to ground speed allows the engine compression to aid in the braking of the vehicle.  
         [0006]     The use of low range extends the life of the transmission because it allows the transmission to operate in its higher gears, as opposed to the lower gears because transmissions are typically designed to have less life in the lower gears than in the higher gears. The use of a low range can also produce torque amplification, most commonly needed in Europe where many vehicles have smaller engines to improve fuel economy but are also used to pull recreational trailers through mountainous terrain in Europe. The increase in ratio spread may also provide for reductions in numerical axle ratio of the vehicle thereby improving the fuel economy during normal highway operation.  
         [0007]     The present invention focuses on a method of shifting the transmission of the vehicle in accordance with the invention which includes providing a transmission connected to a vehicle engine having a predetermined number of gear ratios which are selectable. A transfer case coupled to an output from the transmission and having an output from the transfer case to at least one drive wheel of the vehicle is provided. The transfer case itself includes at least two gear transfer ranges which are selectable and will expand the number of ratios available for shifting during operation of the vehicle. The expansion of the number of available gear ratios is carried out by selecting a gear ratio from the transfer case which provides a final drive ratio either above or below the selected gear ratio of the transmission during operation of the vehicle. The invention also incorporates what is generally known as a dog clutch that functions to disengage the planetary gear set of the transfer case and engage the input shaft directly to provide a direct 1:1 drive ratio.  
         [0008]     The invention can also include a transfer case with the low range gear set modified to produce a 1.6:1 reduction versus a 2.64:1. This may be achieved by having the ring gear be the input and holding the sun gear.  
         [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 diagrammatic view of a motor vehicle driveline having a transfer case incorporating the present invention;  
         [0012]      FIG. 2  is a full, sectional view of a motor vehicle transfer case incorporating a synchronizer according to the present invention;  
         [0013]      FIG. 3  is an enlarged, fragmentary, sectional view of the synchronizer according to the present invention;  
         [0014]      FIG. 4  is a greatly enlarged, fragmentary, sectional view of the synchronizer assembly according to the present invention; and  
         [0015]      FIG. 5  is a schematic diagram of each of the power flow paths according to the present invention.  
         [0016]      FIG. 6  is a full, sectional view of a portion of a synchronizer according to the present invention taken along line  5 - 5  of  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     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.  
         [0018]     Referring now to  FIG. 1 , a four-wheel vehicle drive train is diagrammatically illustrated and designated by the reference number  10 . The four-wheel vehicle drive train  10  includes a prime mover  12  which is coupled to and directly drives a transmission  14 . The transmission  14  may either be an automatic or manual type. The output of the transmission  14  directly drives a transfer case assembly  16  which provides motive power to a primary or rear drive line  20  comprising a primary or rear prop shaft  22 , a primary or rear differential  24 , a pair of live primary or rear axles  26  and a respective pair of primary or rear tire and wheel assemblies  28 .  
         [0019]     The transfer case assembly  16  also selectively provides motive power to a secondary or front drive line  30  comprising a secondary or front prop shaft  32 , a secondary or front differential assembly  34 , a pair of live secondary or front axles  36  and a respective pair of secondary or front tire and wheel assemblies  38 . The front tire and wheel assemblies  38  may be directly coupled to a respective one of the pair of front axles  36  or, if desired, a pair of manually or remotely activateable locking hubs  42  may be operably disposed between the pair of front axles  36  and a respective one of the tire and wheel assemblies  38  to selectively connect same. Finally, both the primary drive line  20  and the secondary drive line  30  may include suitable and appropriately disposed universal joints  44  which function in conventional fashion to allow static and dynamic offsets and misalignments between the various shafts and components. An electronic control unit  46  controls the shifting of the transfer case in order synchronizes it with the transmission  14 .  
         [0020]     The foregoing and following description relates to a vehicle wherein the rear drive line  20  functions as the primary drive line, i.e., it is engaged and operates substantially all the time and, correspondingly, the front drive line  30  functions as the secondary drive line, i.e., it is engaged and operates only part-time or in a secondary or supplemental fashion, such a vehicle commonly being referred to as a rear wheel drive vehicle.  
         [0021]     These designations “primary” and “secondary” are utilized herein rather than “front” and “rear” inasmuch as the may be readily utilized in transmissions and transfer cases wherein the primary drive line  20  is disposed at the front of the vehicle and the secondary drive line  30  is disposed at the rear of the vehicle. Such designations “primary” and “secondary” thus broadly and properly characterize the function of the individual drive lines rather than their specific locations.  
         [0022]     Referring now to  FIGS. 2-7 , the transfer case assembly  16  incorporating the present invention includes a multiple piece, typically cast, metal housing assembly  50  having planar and circular sealing surfaces, openings for shafts and bearings and various recesses, shoulders, flanges, counterbores and the like to receive various components and assemblies of the transfer case assembly  16 . An input shaft  52  includes female or internal splines or gear teeth  54  or other suitable structure which drivingly couple an output of the transmission  14  (illustrated in  FIG. 1 ) to the input shaft  52 . The input shaft  52  is rotatably supported externally by anti-friction bearings such as a ball bearing assemblies  56  and internally by an anti-friction bearing such as a roller bearing assemblies  58 . The roller bearing assemblies  58  are disposed upon a reduced diameter portion of a primary output shaft  60 . An oil seal  62 , positioned between the input shaft  52  and the housing assembly  50 , provides an appropriate fluid tight seal therebetween.  
         [0023]     The transfer case assembly  16  includes a planetary gear speed reduction assembly  80 . The planetary gear speed reduction assembly  80  includes a ring gear  114  that is integrated to the input shaft  52  by a circular disc  102 . The ring gear  114  serves as the input to the planetary gear speed reduction assembly  80 . The ring gear  114  has teeth  112  that engage a plurality of planet gears  88 . The planet gears  88  are rotatably disposed upon roller bearings  92  which in turn are supported by fixed stub shafts  94  or the planet gears  88  can be rotably supported directly on the stub shafts  94 , if desired. The stub shafts  94  are retained and secured within a planet carrier  96  that includes an extension  98 , second extension  99  and male or external splines or gear teeth  100 .  
         [0024]     The planet gears  88  are in constant mesh with gear teeth  86  of a sun gear  82  which is held stationary by an extension  87 .  
         [0025]     The input shaft  52  includes an elongate sleeve or quill  122 . The sleeve or quill  122  is rotatably supported by a pair of roller bearing assemblies  58 . The sleeve or quill  122  of the input shaft  52  includes extension  123  having male splines or gear teeth  126  which are spaced from and axially aligned with the male splines or gear teeth  100  on the second extension  99 .  
         [0026]     The transfer case assembly  16  also includes a synchronizer assembly  130  as best seen in  FIGS. 3 and 4 . The synchronizer assembly  130  includes an outer annular shift collar  132  that is bi-directionally translated from its center position by corresponding bi-directional motion of a shift fork  134  which is received within a circumferential channel or groove  136 . The annular shift collar  132  includes external or male splines or gear teeth  138  that are complementary to and in constant engagement with female or internal splines or gear teeth  142  formed on an annular member  144  of the primary output shaft  60 . The annular shift collar  132  also includes internal or female splines or gear teeth  148  which are complementary to and axially aligned with the male splines  100  on the planetary gear carrier  96  and the male splines  126  of the extension  123  on input shaft sleeve or quill  122 . There is also an inner detented collar  150  which has external or male splines or gear teeth  152  received within and rotates with the annular shift collar  132 . The detented collar  150  includes a circumferential channel  154  which is capable of receiving a contractable circumferential spring  156  which, in its relaxed state, resides within a shallow, oblique-walled circumferential recess  158  in the outer annular shift collar  132 . The circumferential groove  154 , the contractable spring  156  and the oblique-walled circumferential recess  158  cooperate to provide a detenting action between the detented collar  150  and the annular shift collar  132  which provides some resistance to motion of the detented collar  150 , when the detented collar  150  is moved out to the position illustrated in  FIG. 3  and assists return of the detented collar  150  to the center position illustrated in  FIG. 3 . The shift fork  134  is connected to annular shift collar  132 , but allows annular shift collar  132  to rotate with inner right and left circular ball ramp members  164   a  and  164   b . As the shift fork  134  is translated to the left or to the right in  FIG. 2  or  3 , the annular shift collar  132  is also translated to the left or to the right.  
         [0027]     Referring now to  FIGS. 3, 4   a ,  4   b , and  6 , centrally disposed on the inner surface of the annular shift collar  132  is a region of axially extending internal or female splines or gear teeth  162 . The splines or gear teeth  162  engage first or inner left and right circular ball ramp members  164   a  and  164   b  which include splines  166   a  and  166   b  complementary to and engaged with the female splines or gear teeth  162  on the detented collar  150 . The circular members  164   a  and  164   b  include a plurality of oblique walled, ramped recesses  168   a  and  168   b  which receive a like plurality of load transferring balls  172   a  and  172   b . Preferably, the ramped recesses  168   a  and  168   b  extend angularly over approximately 90° to 100°. The circular members  164   a  and  164   b  also include internal or female splines or gear teeth  174   a  and  174   b  that engage complementarily configured male or external splines or gear teeth  178  on a collar or hub  180  that is freely rotatably disposed upon the input shaft sleeve or quill  122 . The splines or gear teeth  178  are non-standard in that only three splines or gear teeth  178  disposed at 120° intervals reside on the collar or hub  180 . It will be appreciated that the primary output shaft  60 , the annular shift collar  132 , the detented collar  150 , annular member  144 , the first or inner clutch members  164   a  and  164   b  and the collar or hub  180  all rotate together.  
         [0028]     Operably disposed between the adjacent faces of the first or inner left and right circular ball ramp members  164   a  and  164   b  is a compression spring  182 . The compression spring  182  may be a Belleville washer, a wave washer, or a circular disc having a plurality of small compression springs disposed along axes parallel to and equidistant from the center line of the primary output shaft  60 .  
         [0029]     The synchronizer assembly  130  includes second or outer left and right circular ball ramp members  184   a  and  184   b  each having a corresponding plurality of oblique walled, ramped recesses  188   a  and  188   b . Preferably, the ramped recesses  188   a  and  188   b  extend angularly over approximately 90 to 100°. As illustrated in  FIG. 6 , the three male or external splines  178  spaced at 120° intervals engage with a corresponding number, i.e., three, spaced apart splines  192  on each second circular member  184   b . The second circular member  184   b  is free to rotate through a limited range of travel relative to the collar or hub  180 . Such range of travel is on the order of eighty to ninety angular degrees and thus the relative rotation and the axial displacement of the circular members  164   a  and  164   b  relative to the corresponding circular member  184   a  and  184   b  is limited.  
         [0030]     It will be appreciated that the ramped recesses  168   a ,  168   b ,  188   a  and  188   b  and the load transferring balls  172   a  and  172   b  is replaced with other analogous mechanical elements that cause axial displacement of the circular members  164   a ,  164   b ,  184   a  and  184   b  in response to relative rotation therebetween. For example, tapered rollers disposed in complementarily configured conical helices may be utilized. It will also be appreciated that the synchronizer assembly  130  may be replaced by other suitable mechanical synchronizers or hydraulic clutch synchronizers, which can be used to engage either the 1:1 gear ratio or the reduced gear ratio.  
         [0031]     Each of the second or circular outer members  184   a  and  184   b  includes a respective shoulder  192   a  and  192   b  which traps and engages a corresponding flat washer  194   a  and  194   b . The opposite faces of each of the flat washers  194   a  and  194   b  engage the internal splines or gear teeth  162  on the detented collar  150 . Thus, as the annular shift collar  132  moves to the left or right from the position as illustrated in  FIG. 3 , the female or internal splines or gear teeth  162  engage and translate one of the flat washers  194   a  or  194   b  in a direction corresponding to the direction of travel of the detented collar  150  and correspondingly translate one of the second or outer circular members  184   a  or  184   b  into engagement with a corresponding left and right friction clutch pack  200   a  or  200   b.    
         [0032]     The left and right friction clutch packs  200   a  and  200   b  include a first plurality of larger clutch plates or discs  202   a  and  202   b . The larger friction plates or discs  202   a  on the left engage complementarily configured splines or gear teeth  204   a  on the bell shaped portion  98  of the planet carrier  96 . A second plurality of smaller diameter friction clutch plates or discs  206   a  on the left engage the splines  178  on the collar or hub  180 . Correspondingly, a first set of larger friction clutch plates or discs  202   b  on the right engage a complementary plurality of internal or female splines or gear teeth  204   b  on the elongate quill or sleeve  122  of the input shaft  52 . A second, interleaved plurality of smaller diameter friction clutch plates or discs  206   b  on the right also engage the splines  178  on the collar or hub  180 .  
         [0033]     Referring to  FIG. 5 , a schematic layout is shown of both of the synchronizer clutch assemblies  200   a  and  200   b . It can be seen how when clutch  200   a  is engaged, the sun gear  82  is held stationary; this creates the reduced gear ratio. When this occurs, clutch  200   b  is not engaged. When it is desired to have the gearset operate at a 1:1 ratio, clutch  200   b  is engaged, and clutch  200   a  is released.  
         [0034]     Referring again to  FIG. 2 , the shift fork  134  is part of a shift operator assembly  210 . The shift fork  134  extends radially from a cylindrical body  212  having a pair of identical cams  212   a  at each end. The cams  212   a  are engaged by a pair of spaced apart cam followers  214  which are secured to a bi-directionally rotatable shift shaft or rail  216 . The shift rail  216  is bi-directionally rotated by an electric motor drive mechanism  218  which selectively, bi-directionally rotates the shift rail  216  and axially translates the shift fork  134  to axially, bi-directionally, move the outer elongate shift collar  132 .  
         [0035]     When a shift is commanded, the shift fork  134  begins to move the outer annular shift collar  132  to the right or to the left from the position illustrated in  FIGS. 2, 3 ,  4   a , and  4   b . In the following explanation, it will be assumed that the outer annular shift collar  132  is being moved to the left as illustrated in  FIGS. 2, 3 ,  4   a , and  4   b  to engage the reduced speed output from the carrier  96  of the planetary gear speed reduction assembly  80 . Translation of the outer annular shift collar  132  to the right engages direct drive from the input shaft  52  but the action of the synchronizer assembly  130  is essentially the same.  
         [0036]     As the outer annular shift collar  132  moves to the left, the contractable spring  156  is driven by the oblique sidewalls  158  into the circumferential channel  154  of the inner detented collar  150 . The detented collar  150  likewise begins to move to the left and the female or internal splines or gear teeth  162  translate the flat washer  194   a  which in turn, translates the second or outer left circular ball ramp member  184   a  into increased frictional engagement with the left friction clutch pack  200   a . The drag so created causes relative rotation between the outer circular ball ramp member  184   a  and the inner circular ball ramp member  164   a  causing the load transferring balls  172   a  to axially separate the circular members  164   a  and  184   a.    
         [0037]     Both the relative rotation of the inner and outer circular members  164   a  and  184   a  and thus their axial separation is limited by the cooperative action of the splines  178  and  192 . The axial separation of the inner and outer circular members  164   a  and  184   a  compresses the friction clutch pack  200   a  and begins to drive the planetary gear carrier  96  into synchronism with the primary output shaft  60 . The compressive force applied to the friction clutch pack assembly  200   a  is controlled and limited by the compressive force generated by the compression spring  182  and, in fact, can be no greater than that force generated by the compression spring  182 . There are two snap rings  160   a  and  160   b  which inhibit circular ball ramp members  164   a  and  164   b  from translating to the left or right, limiting the amount compression spring  182  can be compressed. It must be appreciated that the adjacent first or inner circular members  164   a  and  164   b  must not be permitted to touch or contact one another as this would allow force in excess of that controlled or limited by the compression spring  182  to be applied to the friction clutch packs  200   a  and  200   b  and provide abrupt and unacceptable synchronizer operation.  
         [0038]     In this regard, it should also be appreciated that selection of the spring rate of the compression spring  182  will control the force applied to the friction clutch packs  200   a  and  200   b  and thus the relative speed of synchronization achieved by the synchronizer assembly  130 . That is, a higher or stiffer spring rate will allow more force to be applied to the friction clutch packs  200   a  and  200   b  resulting in faster synchronization and a lower or softer spring rate will achieve a slower rate of synchronization.  
         [0039]     When the speed of the planer carrier  96  matches that of a primary output shaft  60 , the outer annular shift collar  132  may be further advanced to the left such that the female or internal splines or gear teeth  148  may be engaged with the male splines or gear teeth  100  second extension  99 . In this condition, drive torque is transferred directly from the planetary gear carrier  96 , through extension  98 , through second extension  99 , through the outer annular shift collar  132 , through the inter-engaging splines  138  and  142 , through the annular member  144 , and to the primary output shaft  60 .  
         [0040]     The present invention provides a method of shifting the transmission  14  of the vehicle using the vehicle drive train  10 . The method includes providing the transmission  14  which is connected to an engine of the vehicle. The transmission  14  has a predetermined number of gear ratios which are selectable. Additionally, the transfer case  16  is provided that receives an input from the transmission  14 . The transfer case  16  has an output that connected to the primary or secondary wheel assemblies  28 ,  38 . The transfer case  16  includes several gear transfer ranges that are selectable. These selectable gear transfer ranges expand the number of gear ratios available for shifting during the operation of the vehicle by selecting a gear ratio from the transfer case  16  which provides a final drive ratio either at or below at least one of said number of gear ratios of said transmission of the vehicle. The gear transfer ranges which are selected during acceleration of the vehicle will provide an additional shiftable gear range to the transmission. It is possible to have an even greater number of gear transfer ranges within the transfer case  16 . The actual gear ratios achieved will vary depending on the desired ratios. Generally it will be desirable to provide a ratio of less than 1:1 in order to achieve a gear range that is intermediate to the gear range inputted to the transfer case from the transmission. The present invention is configured to provide a ratio of 1.61:1 when the planetary gear speed reduction assembly  80  is engaged.  
         [0041]     A controller  46  is used to select the proper combination of gear ratios from the transmission or transmissions combined with the transfer case during operation of the vehicle. In the embodiment described above the controller  46  sends a control signal to an electrical actuator that actuates the torque synchronizer clutch  130  in order to shift between gear ratios.  
         [0042]     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.