Two-speed full-time transfer case with integrated planetary gearset and synchronized range shift

#The present invention relates generally to a power transfer system for controlling the distribution of drive torque between the front and rear drivelines of a four-wheel drive vehicle. More particularly, the present relates to a full-time transfer case having a two-speed gear reduction unit and an interaxle differential integrated into a planetary gear assembly, a synchronized range shift mechanism for establishing high-range and low-range drive modes, and a biasing clutch for controlling interaxle slip between the front and rear drivelines.

#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, 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. One example of a part-time transfer case is disclosed in commonly-owned U.S. Pat. No. 4,770,280.

#It is also known to use “on-demand” power transfer systems for automatically directing power to the non-driven wheels, without any input or action on the part of the vehicle operator, when traction is lost at the driven wheels. Typically, the on-demand feature is incorporated into the transfer case by replacing the mode shift mechanism with a clutch assembly that is interactively associated with an electronic control system and a sensor arrangement. During normal road conditions, the clutch assembly is maintained in a non-actuated condition such that drive torque is only delivered to the driven wheels. However, when the sensors detect a low traction condition at the driven wheels, the clutch assembly is automatically actuated to deliver drive torque to the non-driven wheels. The amount of drive torque transferred through the clutch assembly can be varied as a function of specific vehicle dynamics detected by the sensor arrangement. One example of an on-demand power transfer system is disclosed in commonly-owned U.S. Pat. No. 5,323,871.

#FIG. 1 is a schematic representation of a four-wheel drive motor vehicle equipped with a full-time power transfer system according to the present invention;

#FIG. 2 is a sectional view of a full-time two-speed transfer case constructed according to a preferred embodiment of the present invention;

#FIG. 3 is an enlarged partial view taken from FIG. 2 showing components of the synchronized range shift mechanism in greater detail;

#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.

#As will be detailed hereinafter with greater specificity, transfer case 20 is equipped with a planetary gear assembly 42, a range clutch assembly 44, and a mode clutch assembly 46. Planetary gear assembly 42 includes a first planetary gearset 48 and a second planetary gearset 50 interconnected through a common carrier assembly 52. Range clutch assembly 44 is operable to couple components of first planetary gearset 48 for driving carrier assembly 52 at either of a first (high-range) speed ratios or a second (low-range) speed ratio. Second planetary gearset 50 of planetary gear assembly 42 functions as an interaxle differential having carrier assembly 52 as its input with other components thereof operably coupled to front output shaft 30 and rear output shaft 40 of transfer case 20. Additionally, mode clutch assembly 48 is operable to control the magnitude of speed differentiation and torque biasing between rear output shaft 40 and rear output shaft 30. Power transfer system 10 further includes a power-operated actuator assembly 54 for controlling actuation of range clutch assembly 44 and mode clutch assembly 46, a sensor group 56 for sensing dynamic and operational characteristics of the motor vehicle and generating sensor input signals indicative thereof, and a controller 58 for generating control signals in response to the sensor input signals. Power transfer system 10 also includes a mode select mechanism 60 for permitting the vehicle operator to select one of the available drive modes. In particular, controller 58 functions to control actuation of power-operated actuator assembly 54 in response to the mode signal sent to controller 58 from mode select mechanism 60 that is indicative to the particular mode selected.

#With particular reference now to FIGS. 2 through 4 of the drawings, transfer case 20 is shown to include an input shaft 62 rotatably supported by a bearing assembly 64 from a housing 66. Input shaft 62 is adapted for connection to an output shaft of transmission 18. Likewise, front output shaft 30 and rear output shaft 40 are also rotatably supported by housing 66. As noted, planetary gear assembly 42 includes a first gearset 48 interconnected to second gearset 50 via a common carrier assembly 52. First gearset 48 includes a ring gear 68, a first sun gear 70, and a set of first planet gears 72 each meshed with ring gear 68 and first sun gear 70. Planet gears 72 are rotatably supported on long pins 74 and short pins 76, each of which extends between first and second carrier rings 78 and 80, respectively, of carrier assembly 52. First sun gear 70 is shown fixed via a splined connection 84 for rotation with and axial sliding movement on a quill shaft 86 journalled on rear output shaft 40 and which is fixed via a splined connection 88 for rotation with input shaft 62. As such, first sun gear 70 is always driven by input shaft 62.