Abstract:
A three-speed transfer case for providing a direct drive connection between the input shaft and the output shafts, a low-range drive connection and an ultra low-range drive connection. The ability to choose between the distinct speed ratio drive connections permits the vehicle operator to best match the road conditions or off-road terrain to the tractive requirements of the motor vehicle.

Description:
FIELD OF THE INVENTION 
     The present inventions generally to transfer cases for used in four-wheel drive motor vehicles and, more particularly, to a multi-speed transfer case. 
     BACKGROUND OF THE INVENTION 
     Due to growing consumer demand for four-wheel drive vehicles, a plethora of different power transfer systems are currently utilized for directing power (i.e., drive torque) to all four wheels of the vehicle. For example, in many “part-time” power transfer systems, a transfer case is installed between the front and rear drivelines and is normally operable in a two-wheel drive mode for delivering drive torque to the driven wheels. However, when the four-wheel drive mode is desired, a mode shift mechanism is selectively actuated by the vehicle operator for directly coupling the non-driven wheels to the driven wheels for establishing a part-time or locked four-wheel drive mode. 
     A significant number of the transfer cases discussed above are equipped with a gear reduction unit and a range shift mechanism operable for permitting the vehicle operator to choose between a high-range and a low-range drive mode. The particular low-range reduction ratio established is dictated by the gear geometry of the gear components associated with the reduction unit and, as such, all conventional two-speed transfer cases have a fixed ratio which ranges between about 2.5 to 4.5 to 1.0. True off-road enthusiasts desire the higher ratio which provides greater tractive ability over the most severe terrain. In contrast, the lower ratio is considered to provide the best tractive results for most typical road and severe weather conditions. Thus, the need exists to provide a multi-speed transfer case that can provide both a high and low reduction ratio mode in addition to the direct ratio mode. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a transfer case for use in four-wheel drive vehicles that is capable of establishing at least three distinct speed ratio drive connections between the input shaft and the output shafts. 
     As a related object, the transfer case is operable to establish a high-range direct drive connection, a low-range reduction ratio drive connection, and an ultra low-range reduction ratio drive connection. 
     As a further related object, the transfer case of the present invention is also operable to establish a mid-range drive connection. 
     As a further object, the three-speed transfer case of the present invention is operable to establish full-time and part-time four-wheel drive modes. 
     In accordance with a preferred embodiment of the present invention, the three-speed transfer case includes and input shaft, first and second output shafts, and a first planetary gearset having a first sun gear driven by the input shaft, a first ring gear fixed to a stationary member, and a set of first pinions meshed with the first sun gear and the first ring gear and which are rotatably supported from a first carrier. The transfer case further includes a second planetary gearset including a second sun gear, a third sun gear, a second ring gear, a second carrier driving the first output shaft, a set of second pinions rotatably supported by the second carrier and meshed with the second ring gear and the second sun gear, and a set of third pinions rotatably supported by the second carrier and meshed with the third sun gear and the second pinions. A transfer mechanism is provided for driving the second output shaft. The transfer case also includes a range clutch operable in a first state to couple the second ring gear to the input shaft and in a second state to couple the second ring gear to the first carrier; a lock-out clutch operable in a first state to permit rotation of the second sun gear and in a second state to couple the second sun gear to the stationary member; and a mode clutch operable in a first state to couple the transfer mechanism to the third sun gear, in a second state to couple the transfer mechanism to the third sun gear and the second carrier, and in a third state to couple the transfer mechanism to the second carrier. 
     These and other objects, features and advantages of the present invention will be clearly illustrated and understood upon study of the following written description when taken in conjunction with the following drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a four-wheel drive vehicle equipped with a multi-speed transfer case according to the present invention; 
     FIG. 2 is a schematic view of the multi-speed transfer case operating in a full-time high-range four-wheel drive mode; 
     FIG. 3 is a schematic view, similar to FIG. 2, showing the multi-speed transfer case operating in a locked high-range four-wheel drive mode; 
     FIG. 4 shows the multi-speed transfer case operating in a neutral mode; 
     FIG. 5 shows the multi-speed transfer case operating in a full-time low-range four-wheel drive mode; 
     FIG. 6 shows the multi-speed transfer case operating in a locked low-range four-wheel drive mode; 
     FIG. 7 shows the multi-speed transfer case operating in a locked ultra low-range four-wheel drive mode; 
     FIG. 8 shows the multi-speed transfer case operating in a locked mid-range four-wheel drive mode; and 
     FIG. 9 is a chart listing the position of the various clutches used to establish each of the above-listed operational modes. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, a drivetrain for a four-wheel drive vehicle is schematically shown interactively associated with a power transfer system  10  of the present invention. The motor vehicle drivetrain includes a front driveline  12  and a rear driveline  14  both driveable from a source of power, such as an engine  16 , through a transmission  18  which may be of the manual or automatic type. In the particular embodiment shown, the drivetrain includes a transfer case  20  for transmitting drive torque from engine  16  and transmission  18  to front driveline  12  and rear driveline  14 . Front driveline  12  includes a pair of front wheels  22  connected at opposite ends of a front axle assembly  24  having a front differential  26  coupled to one end of a front drive shaft  28 , the opposite end of which is coupled to a front output shaft  30  of transfer case  20 . Similarly, rear driveline  14  includes a pair of rear wheels  32  connected at opposite ends of a rear axle assembly  34  having a rear differential  36  coupled to one end of a rear drive shaft  38 , the opposite end of which is interconnected to a rear output shaft  40  of transfer case  20 . 
     Transfer case  20  includes an input shaft  42  that is rotatably supported by a bearing assembly from housing  44  input shaft  42  is driven by the output of transmission  18 . Rear output shaft  40  and front output shaft  30  are also rotatably supported from housing  44  by suitable bearing assemblies. A first planetary gearset  46  includes a first sun gear  48  driven by input shaft  42 , a first ring gear  50  fixed to housing  44 , and a set of first pinions  52  each meshed with first sun gear  48  and first ring gear  50 . First pinion gears  52  are rotatably supported on pins extending between a first carrier ring  54  and a second carrier ring  56  which are interconnected to define a first carrier  58 . Transfer case  20  further includes a second planetary gearset  60  having a second ring gear  62 , a second sun gear  64 , a third sun gear  66 , a set of second pinions  68 , and a set of third pinions  70 . Second pinions  68  are rotatably supported on pins extending between a third carrier ring  72  and a fourth carrier ring  74  which are interconnected to define a second carrier  76 . Second pinions  68  are meshed with second ring gear  62  and second sun gear  64 . Third pinions  70  are rotatably supported on pins extending between fourth carrier ring  74  and a fifth carrier ring  78  such that they are also supported by second carrier  76 . Third pinions  70  are meshed with third sun gear  66  and second pinions  68 . 
     Transfer case  20  also includes a range clutch  80  that is operable for selectively coupling output components of first gearset  46  to an input component of second planetary gearset  60 . In particular, second ring gear  62  includes a shaft segment  82  on which a range sleeve  84  is splined for sliding movement between three distinct range position. Range sleeve  84  is moveable between a high-range (“H”) position, a neutral (“N”) position and a low-range (“L”) position. In the H position, clutch teeth on range sleeve  84  engage clutch teeth on first sun gear  48  such that a direct drive ratio (1:1) is established between input shaft  42  and second ring gear  62 . In the L position, the clutch teeth on range sleeve  84  engage clutch teeth on second carrier ring  56  such that a first reduced ratio of approximately 2.72:1 is established between input shaft  42  and second ring gear  62 . Specifically, since first ring gear  50  is braked against rotation, rotation of input shaft  42  causes first carrier  58  to be driven at a reduced speed dictated by the gear ratios of the components of first planetary gearset  46 . The 2.72:1 ratio is established when first ring gear  50  has 91 teeth, first sun gear  48  has 53 teeth, and each first pinion  52  has 19 teeth. Finally, when range sleeve  84  is located in its N position, the drive connection between input shaft  42  and second ring gear  62  is interrupted. 
     As seen, second carrier  76  drives rear output shaft  40  via third carrier ring  72  being directly fixed thereto. Second sun gear  64  is shown to include an elongated shaft segment  86  that is journalled on rear output shaft  40 . Transfer case  20  also includes a lock-out clutch  88  that is operable for selectively coupling second sun gear  64  to housing  44 . In particular, lock-out clutch  88  includes a brake plate  90  fixed to housing  44  and a lock-out sleeve  92  that is splined for sliding movement on shaft segment  86  between a first position (“X”) and a second position (“Y”). In the X position, clutch teeth on lock-out sleeve  92  are released from engagement with clutch teeth on brake plate  90  such that second sun gear  64  is free to rotate relative to housing  44 . In contrast, movement of lock-out sleeve  92  to its Y position results: in engagement of its clutch teeth with the clutch teeth on brake plate  90  so as to prevent rotation of second sun gear  64 . 
     Transfer case  20  is further shown to include a transfer mechanism  94  including a drive sprocket  96  journalled on shaft segment  86  of second sun gear  64 , a driven sprocket  98  fixed to first output shaft  30 , and a power chain  100  interconnecting driven sprocket  98  to drive sprocket  96 . A mode clutch  102  is operable for selectively coupling drive sprocket  96  to at least one of third sun gear  66  and second carrier  76 . Mode clutch  102  includes a mode sleeve  104  that is splined to drive sprocket  96  for sliding movement between three distinct mode positions. Mode sleeve  104  is moveable between a first mode position (“A”), a second mode position (“B”), and a third mode position (“C”). When mode sleeve  104  is in its A position, its clutch teeth mesh with clutch teeth formed on a clutch ring segment  106  of third sun gear  66  such that third sun gear  66  is connected to transfer mechanism  94  for transferring drive torque to front output shaft  30 . When mode sleeve  104  is in its B position, its clutch teeth are maintained in meshed engagement with the clutch teeth on clutch ring segment  106  of third sun gear  66  and further engage clutch teeth on a clutch ring segment  108  fixed to fourth carrier ring  74 , whereby both second carrier  76  and third sun gear  66  are coupled to transfer mechanism  94 . Finally, movement of mode sleeve  104  to its C position causes its clutch teeth to be released from engagement with the clutch teeth on clutch ring segment  106  of third sun gear  66  while maintaining engagement with the clutch teeth on clutch ring segment  108  driven by second carrier  76 . In this position, mode sleeve  104  only couples second carrier  76  to transfer mechanism  94 . 
     Power transfer system  10  is shown to include a power-operated actuator assembly  110  for controlling movement of range sleeve  84 , lock-out sleeve  92 , and mode sleeve  104  to establish at least seven different operational modes. Power transfer system  10  also includes a mode selector mechanism  112  for permitting the vehicle operator to select a desired operational mode, and a control unit  114  which functions to control activation of actuator assembly  110  in response to the particular mode signal sent thereto by mode select mechanism  112 . Preferably, actuator assembly  110  includes a rotary actuator, such as an electric gearmotor  116  which rotates a drive mechanism capable of coordinating movement of the three sleeves to establish a selected operational mode. The drive mechanism is interconnected to an output member  118  of gearmotor  116  and includes a sector plate  120  that is rotatably driven through a range of angular motion by output member  118  in response to activation of electric gearmotor  116 . 
     To generate axial movement of range sleeve  84 , sector plate  120  includes a first slot  122  within which a follower  124  is retained that is fixed to a first fork  126 . Fork  126  is also connected to range sleeve  84 . The contour of first slot  122  is adapted to control movement of range sleeve  84  between its H, N and L range positions in response to bi-directional rotation of sector plate  120 . Likewise, sector plate  120  also includes a second slot  130  within which a follower  132  is retained that is fixed to a second fork  134 . Second fork  134  is also connected to lock-out sleeve  92 . The contour of second slot  130  is adapted to control movement of lock-out sleeve  92  between its X and Y positions in response to bidirectional rotation of sector plate  120 . Finally, sector plate  120  includes a third slot  136  within which a follower  138  is retained that is fixed to a third fork  140 . Third fork  140  is also connected to mode sleeve  104 . The contour of third slot  136  is adapted to control movement of mode sleeve  104  between its A, B and C positions in response to bi-directional rotation of sector plate  120 . With this arrangement, a single power-operated device is capable of coordinating movement of the various sleeves to establish the six different operational modes. As an alternative, first slot  122  and slot  130  could be profiled end surfaces of sector plate  120  with their corresponding followers  124  and  132  biased by springs in continuous contact therewith. It is also possible to utilize separate electric actuators, similar to gearmotor  116 , for controlling independent movement of first fork  126 , second fork  134  and third fork  140 . 
     According to one embodiment of the present invention, sector plate  120  may be rotated to any one of seven distinct sector positions to establish a corresponding number of operational modes. These modes include a full-time four-wheel high-range drive mode, a locked or part-time four-wheel high-range drive mode, a neutral mode, a full-time four-wheel low-range drive mode, a part-time four-wheel low-range drive mode, a part-time four-wheel ultra low-range drive mode, and a part-time four-wheel mid-range drive mode. The particular four-wheel drive mode selected is established by the position of first pin  124  in first slot  122 , the position of second pin  132  in second slot  130 , and the position of third pin  138  in third slot  136 . In operation, the vehicle operator selects a desired operational mode via actuation of mode select mechanism  112  which, in turn, sends a mode signal to controller  114  that is indicative of the selection. Thereafter, controller  114  generates an electric control signal that is applied to gearmotor  116  for controlling the rotated position of sector plate  120 . It should be understood that transfer case  20  can be arranged to provide any number of the seven different drive. modes to provide a multi-speed power transfer device. 
     Mode select mechanism  112  can take the form of any mode selector device which is under the control of the vehicle operator for generating a mode signal indicative of the specific mode selected. In one form, the mode selector device may be in an array of dash-mounted push button switches. Alternatively, the mode selector may be a manually-operable shift lever sequentially moveable between a plurality of positions corresponding to the available operational modes which, in conjunction with a suitable electrical switch arrangement, generates a mode signal indicating the selected mode. In either form, mode select mechanism  112  offers the vehicle operator the option of deliberately choosing between the various operative drive modes. 
     When the full-time four-wheel high-range drive mode is selected, sector plate  120  is rotated to a first sector position causing range sleeve  84  to be located in its H position, lock-out sleeve  92  to be located in its X position, and mode sleeve  104  to be located in its A position, as best shown in FIG.  2 . This mode does not provide any speed reduction between input shaft  42  and second ring gear  62  but does provide a torque split between rear output shaft  40  (via second carrier  76 ) and front output shaft  30  (via third sun gear  66  and transfer mechanism  94 ). Thus, the full-time four-wheel drive mode is established with speed differentiation permitted between the output shafts. In addition, second sun gear  64  is disconnected from the power flow paths and does not carry any loading. 
     If mode selector  112  signals selection of the part-time four-wheel high-range drive mode, gearmotor  116  is activated to rotate sector plate  120  to a second sector position for locating range sleeve  84  in its H position, locating lock-out sleeve  92  in its X position, and locating mode sleeve  104  in its B position. This drive mode is shown in FIG.  3 . With mode sleeve  104  in its B position, second carrier  76  and third sun gear  66  are directly coupled for common rotation such that no speed differentiation is permitted between rear output shaft  40  and first output shaft  30 . 
     Referring to FIG. 4, transfer case  20  can also be shifted into a neutral mode for purposes of towing. When mode selector  112  indicates selection of this mode, gearmotor  116  rotates sector plate  120  to a third sector position. In particular, movement of sector plate  120  to its third sector position causes range sleeve  84  to be located in its N position, mode sleeve  104  to be located its A position, and lock-out sleeve  92  to be located in its X position. As such, no drive torque is transmitted from input shaft  42  through first gearset  46  to second gearset  60 . 
     Selection of the full-time four-wheel low-range drive mode results in rotation of sector plate  120  to a fourth sector position whereat range sleeve  84  is located in its L position, lock-out sleeve  92  is located in its X position, and mode sleeve  104  is located in its A position. This mode for transfer case  20  is shown in FIG. 5 of the drawings. In particular, second ring gear  62  is driven at the reduced ratio of about 2.72:1 relative to input shaft  42  due to range sleeve  84  coupling ring gear  62  to first carrier  58 . With mode sleeve  104  in its A position, third sun gear  66  is coupled to front output shaft  30  via transfer mechanism  94  while rear output shaft  40  is driven by second carrier  76 . Thus, speed differentiation between the output shafts is permitted and the full-time four-wheel drive mode is established. 
     Referring to FIG. 6, transfer case  20  is now shown operating in its part-time four-wheel low-range drive mode that is established when sector plate  120  is rotated to a fifth sector position. In this sector position, range sleeve  84  is located in its L position, mode sleeve  104  is located in its B position, and lock-out sleeve  92  is located in its X position. Thus, the low-range drive connection between input shaft  42  and second ring gear  62  is established while mode sleeve  104  couples third sun gear  66  to second carrier  76  so as to prevent speed differentiation between rear output shaft  40  and front output shaft  30  and establish the part-time four-wheel drive mode. 
     Another operational mode, referred to as the part-time four-wheel ultra low-range drive mode is shown in FIG. 7 with range sleeve  84  located in its L position, mode sleeve  104  in its C position, and lock-out sleeve  92  in its Y position. This location of the sleeves is a result of sector plate  120  being rotated to a sixth sector position from its fifth sector position. As such, the 2.72:1 ratio established across first planetary gearset  46  is compounded by an approximately 1.68:1 ratio that is established through second planetary gearset  60 , thereby establishing an overall gear ratio reduction of about 4.57:1 between input shaft  42  and second carrier  76 . The overall reduction ratio of about 4.57:1 establishes the ultra low-range and permits aggressive off-road driving. In this. mode, second carrier  76  drives both rear output shaft  40  (via third carrier ring  72 ) and front output shaft  30  (via fourth carrier ring  74 , mode sleeve  104  and transfer mechanism  94 ) so as to establish the part-time four-wheel drive mode. As seen, with mode sleeve  104  in its C position, third sun gear  66  is disconnected from the power path and clutch plate segment  108  of carrier ring  74  is coupled to drive sprocket  96 . Also, lock-out sleeve  92  acts to couple second sun gear  64  to brake plate  90  such that second sun gear  64  is fixed against rotation. Since second sun gear  64  is stationary, driven rotation of second ring gear  62  causes second carrier  76  to rotate at the reduced speed relative thereto, thereby establishing the second speed reduction ratio of about 1.64:1. To establish this particular ratio across second planetary gearset  60 , second ring gear  62  has 87 teeth, second sun geatr  64  has 59 teeth, third sun gear  66  has 34 teeth, second pinions  68  each have 14 teeth, and third pinions  70  each have 19 teeth. Thus, transfer case  20  provides several distinct speed ranges which can be selected to accommodate the particular road conditions and/or off-road terrain that the vehicle encounters. 
     As a further option, transfer case  20  is operable, if so desired, to provide a fourth speed range in addition to the previously described high-range, low-range and ultra-low range. Specifically, a part-time four-wheel mid-range drive mode can be established when sector plate  120  is rotated from its sixth sector position to a seventh sector position. In this sector position, as shown in FIG. 8, range sleeve  84  is located in its H position, mode sleeve  104  is located in its C position, and lock-out sleeve  92  is located in its Y position. As such, the 1:1 ratio established by first planetary gearset  46  is compounded by the 1:68:1 ratio established across second planetary gearset  60 , thereby establishing the 1.68:1 ratio between input shaft  42  and second carrier  76 . This mid-range speed ratio between the 1:1 high-range and the 2.72:1 low-range can be mode available when road-terrain conditions warrant its use. 
     It will be appreciated that the first and second reduction ratios, and thus the compounded ratio, are merely exemplary and are dictated by the number of teeth provided on each gear component. Those skilled in the gear art will appreciate that alternative reduction ratios can be established utilizing the arrangement of gear components described in association with the present invention. Preferred embodiments have been disclosed to provide those skilled in the art an understanding of the best mode currently contemplated for the operation and construction of the present invention. The invention being thus described, it will be obvious that various modifications can be made without departing from the true spirit and scope of the invention, and all such modifications as would be considered by those skilled in the art are intended to be included within the-scope of the following claims.