On-demand two-speed transfer case for four-wheel drive hybrid vehicle

#The present invention relates generally to hybrid drive systems for motor vehicles, and, more specifically, to a hybrid transfer case for use in four-wheel drive vehicles.

#Automobile manufacturers are actively working to develop alternative powertrain systems in an effort to reduce the level of pollutants exhausted into the air by conventional powertrains equipped with internal combustion engines. Significant development has been directed to electric vehicles and fuel cell vehicles. Unfortunately, these alternative powertrain systems suffer from several disadvantages and, for all practical purposes, are still under development. However, several different hybrid electric vehicles (HEV) have recently been offered for sale. These hybrid vehicles are equipped with an internal combustion engine and an electric motor that can be operated independently or in combination to drive the vehicle.

#There are two types of hybrid vehicles, namely, series hybrid and parallel hybrid. In a series hybrid vehicle, power is delivered to the wheels by the electric motor which draws electrical energy from the battery. The engine is used in series hybrid vehicles to drive a generator which supplies power directly to the electric motor or charges the battery when the state of charge falls below a predetermined value. In parallel hybrid vehicles, the electric motor and the engine can be operated independently or in combination pursuant to the running conditions of the vehicle. Typically, the control strategy for such parallel hybrid vehicles utilizes a low-load mode where only the electric motor is used to drive the vehicle, a high-load mode where only the engine is used to drive the vehicle, and an intermediate assist mode where the engine and electric motor are both used to drive the vehicle. Regardless of the type of hybrid drive system used, hybrid vehicles are highly modified versions of conventional vehicles that are expensive due to the componentry, required control systems, and specialized packaging requirements.

#FIG. 1 is a schematic view showing a hybrid powertrain for a four-wheel drive vehicle in accordance with the present invention;

#FIG. 2 is a sectional view of the transfer case associated with the hybrid powertrain shown in FIG. 1;

#FIG. 3 is an enlarged partial sectional view showing the input clutch assembly in greater detail;

#Referring to FIG. 1 of the drawings, a four-wheel drive powertrain 10 for a hybrid motor vehicle is shown to include an internal combustion engine 12, a transmission 14 and a transfer case 16 arranged to transferred motive power (i.e., drive torque) from engine 12 and transmission 14 to a primary driveline 18 and a secondary driveline 20. In the particular arrangement shown, primary driveline 18 is the rear driveline and includes a pair of rear wheels 22 connected to a rear differential unit 24 associated with a rear axle assembly 26. A rear prop shaft 28 interconnects rear differential unit 24 to a rear output shaft 30 of transfer case 16. Secondary driveline 20 is the front driveline and includes a pair of front wheels 32 connected to a front differential unit 34 associated with a front axle assembly 36. A front prop shaft 38 interconnects differential unit 34 to a front output shaft 40 of transfer case 16. Powertrain 10 is also shown to be associated with a powertrain control system 42 generally shown to include an array of vehicle sensors 44, a battery 46 and a controller 48. As will be detailed, controller 48 is operable, among other things, to control actuation of two major sub-systems integrated into transfer case 16. These sub-systems include an electric motor/generator unit and a hydraulic clutch and brake control system.

#Referring primarily to FIGS. 2 through 7, the components of transfer case 16 are shown in sufficient detail to provide a clear understanding of its construction and operation. To this end, transfer case 16 is shown to include a housing 50, an input shaft 52 driven by the output shaft of transmission 14, a mainshaft 54, and an input clutch assembly 56 operably disposed between input shaft 52 and mainshaft 54. Transfer case 16 further includes a planetary gearset 58 having an input member driven by mainshaft 54 and an output member adapted to drive rear output shaft 30, and a transfer assembly 60. A direct clutch assembly 62 is shown operably disposed between the output member of planetary gearset 58 and input shaft 52. In addition, a low brake assembly 64 is shown operably disposed between a reaction member of planetary gearset 58 and a portion of housing 50, transfer case 16 also include a transfer clutch assembly 66 that is operably disposed between transfer assembly 60 and front output shaft 40. Finally, an electric motor/generator (M/G) unit 68 is shown to include a stator 70 fixed to housing 50 and a rotor 72 fixed to mainshaft 54.

#As best seen from FIG. 3, input shaft 52 is rotatably supported from housing 50 by a bearing assembly 74 and a forward end of tubular mainshaft 54 is supported by a bearing assembly 76 on input shaft 52 for rotation relative thereto. Input clutch assembly 56 is operable in an applied state to couple mainshaft 54 for rotation with input shaft 52 and is further operable in a released state to permit relative rotation therebetween. Input clutch assembly 56 is shown to be a spring-released pressure-applied type of arrangement. Input clutch assembly 56 includes an annular drive hub 78 fixed to input shaft 52, a clutch drum 80 fixed to rotor 72, and a multi-plate clutch pack 82 therebetween. Clutch pack 82 includes a set of inner plates 84 splined to drive hub 78 and which are interleaved with a set of outer plates splined to drum 80. Clutch pack 82 is disposed between a reaction plate 88 splined to drum 80 and a piston 92.