Electronically-controlled coupling for all-wheel drive system

#The present invention relates generally to hydraulic couplings for use in motor vehicle driveline applications for limiting slip and transferring torque between rotary members. More specifically, a drive axle assembly for an all-wheel drive vehicle is disclosed having a pair of hydraulic couplings each having a fluid pump, a multi-plate clutch assembly, and a fluid distribution system operable to control actuation of the clutch assembly.

#In all-wheel drive vehicles, it is common to have a secondary drive axle that automatically receives drive torque from the drivetrain in response to lost traction at the primary drive axle. In such secondary drive axles, it is known to provide a pair of clutch assemblies connecting each axleshaft to a prop shaft that is driven by the drivetrain. For example, U.S. Pat. No. 4,650,028 discloses a secondary drive axle equipped with a pair of viscous couplings. In addition, U.S. Pat. Nos. 5,964,126, 6,095,939, 6,155,947 and 6,186,258 each disclose secondary drive axles equipped with a pair of pump-actuated multi-plate clutch assemblies. In contrast to these passively-controlled secondary drive axles, U.S. Pat. No. 5,699,888 teaches of a secondary drive axle having a pair of multi-plate clutches that are actuated by electromagnetic actuators that are controlled by an electronic control system.

#In response to increased consumer demand for motor vehicles with traction control systems, hydraulic couplings are currently being used in a variety of driveline applications. Such hydraulic couplings rely on hydromechanics and pressure-sensitive valve elements to passively respond to a limited range of vehicle operating conditions. These hydraulic couplings are susceptible to improvements that enhance their performance, such as a more controlled response to a wider range of vehicle operating conditions. With this in mind, a need exists to develop improved hydraulic couplings that advance the art.

#Further objects, features and advantages of the present invention will become readily apparent from the following detailed specification and the appended claims which, in conjunction with the drawings, set forth the best mode now contemplated for carrying out the invention. Referring to the drawings:

#FIG. 1 is a schematic view of a motor vehicle drivetrain equipped with a secondary drive axle assembly constructed in accordance with the present invention;

#FIG. 2 is a sectional view of the secondary drive axle assembly of the present invention;

#In general, the present invention is directed to a hydromechanical limited slip and torque transfer device, hereinafter referred to as a drive axle assembly, for use in connecting the drivetrain to a pair of axleshafts associated with a secondary driveline of an all-wheel drive vehicle. However, the drive axle assembly can also find application in other driveline applications including, but not limited to, limited slip differentials of the type used in full-time transfer cases and front-wheel drive transaxles. Furthermore, this invention advances the technology in the field of actively-controlled hydraulically-actuated couplings of the type requiring pressure relief and thermal unloading to prevent damage to the driveline components.

#With reference to FIG. 1, a schematic layout for a vehicular drivetrain 10 is shown to include a powertrain 12 driving a first or primary driveline 14 and a second or secondary driveline 16. Powertrain 12 includes an engine 18 and a transaxle 20 arranged to provide motive power (i.e., drive torque) through a front differential (not shown) to a pair of wheels 22 associated with primary driveline 14. In particular, primary driveline 14 includes a pair of halfshafts 24 connecting wheels 22 to the front differential associated with transaxle 20. Secondary driveline 16 includes a power take-off unit (PTU) 26 driven by transaxle 20, a prop shaft 28 driven by PTU 26, a pair of axleshafts 30 connected to a pair of wheels 32, and a drive axle assembly 34 operable to transfer drive torque from propshaft 28 to one or both axleshafts 30.

#Referring to FIGS. 2 through 7, the components associated with drive axle assembly 34 will be now detailed. Drive axle assembly 34 includes a multi-piece housing 40, an input shaft 42, a first hydraulic coupling 44, and a rear differential drive module 46. Input shaft 42 is rotatably supported in housing 40 by a bearing assembly 48 and sealed relative thereto via a seal assembly 50. A yoke 52 is secured to input shaft 42 and is adapted for connection to propshaft 28. Drive module 46 includes a pinion shaft 54, a bevel-type differential gearset 56, a pair of output shafts 58 and 60 adapted for connection to axleshafts 30, and a second hydraulic coupling 62. In operation, first hydraulic coupling 44 is operable to transfer drive torque from input shaft 42 to pinion shaft 54 in response to excessive interaxle speed differentiation between propshaft 28 and differential gearset 56. Second hydraulic coupling 62 is operable to limit intra-axle slip in response to excessive speed differentiation between output shafts 58 and 60.