Transfer case with synchronized range shift and controllable bi-directional clutch

#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 invention 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 range shift mechanism for establishing high-range and low-range drive modes, and a controllable bi-directional overrunning clutch for controlling interaxle slip between the front and rear drivelines.

#Four-wheel drive vehicles are in great demand due to the enhanced on and off road traction control they provide. In many four-wheel drive vehicles, a transfer case is installed in the drivetrain and is normally operable to deliver drive torque to the primary driveline for establishing a two-wheel drive mode. The transfer case is further equipped with a clutch assembly that can be selectively or automatically actuated to transfer drive torque to the secondary driveline for establishing a four-wheel drive mode. These “mode” clutch assemblies can range from a simple dog clutch that is operable for mechanically shifting between the two-wheel drive mode and a “locked” (i.e., part-time) four-wheel drive mode to a more sophisticated automatically-actuated multi-plate clutch for providing an “on-demand” four-wheel drive mode.

#On-demand four-wheel drive systems are able to provide enhanced traction and stability control and improved operator convenience since the drive torque is transferred to the secondary driveline automatically in response to lost traction at the primary driveline. An example of passively-controlled on-demand transfer case is shown in U.S. Pat. No. 5,704,863 where the amount of drive torque transferred through a pump-actuated clutch pack is regulated as a function of the interaxle speed differential. In contrast, actively-controlled on-demand transfer cases include a clutch actuator that is adaptively controlled by an electronic control unit in response to instantaneous vehicular operating characteristics detected by a plurality of vehicle sensors. U.S. Pat. Nos. 4,874,056, 5,363,938 and 5,407,024 disclose various examples of adaptive on-demand four-wheel drive systems.

#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 integrated planetary gear assembly and the range shift mechanism in greater detail;

#Referring now to the drawings, a drivetrain for a full-time 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 44, and a mode clutch 46. Planetary gear assembly 42 includes a first planetary gearset 48 and a second planetary gearset 50 interconnected through a common carrier 52. Range clutch 44 is operable to couple components of first planetary gearset 48 for driving carrier 52 at either of a first (high-range) speed ratio or a second (low-range) speed ratio. Second planetary gearset 50 of planetary gear assembly 42 functions as an interaxle differential having carrier 52 as its input with other components thereof operably coupled to front output shaft 30 and rear output shaft 40. Additionally, mode clutch 46 is operable to control the magnitude of speed differentiation and torque distribution between rear output shaft 40 and front output shaft 30. Power transfer system 10 further includes a power-operated actuator 54 for controlling coordinated actuation of range clutch 44 and mode clutch 46, a mode select mechanism 56 operable to permit the vehicle operator to select one of the available drive modes, and a controller 58 for controlling actuation of actuator 54. In particular, controller 58 functions to control actuation of power-operated actuator 54 in response to the mode signal sent to controller 58 from mode select mechanism 56 for establishing the particular mode selected.

#With particular reference now to FIGS. 2 through 5 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. As noted, planetary gear assembly 42 includes a first gearset 48 interconnected to second gearset 50 via carrier 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 52 A stub shaft segment 82 of first sun gear 70 is shown fixed via a splined connection 84 for rotation with input shaft 62.