Transfer case

A transfer case includes a planetary differential including an input, a first output and a second output, a sprocket journalled on the second output, and a sleeve driveably connected to the second output, for (i) releaseably connecting the first output to the sleeve, (ii) releaseably connecting the sprocket to the sleeve, (iii) releaseably connecting the first output and the sprocket to the sleeve, and (iv) disconnecting the sprocket and first output from the sleeve.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to an apparatus for a motor vehicle driveline that selectively produces two-wheel drive, four-wheel drive, all-wheel drive and neutral operation of the driveline.

2. Description of the Prior Art

Some modern automatic transmissions have integral with the transmission itself the ability to shift among two-wheel drive, four-wheel drive, and all-wheel drive ranges. Automatic transmissions also are able to produce a lower speed ratio for use while towing that the speed ratio that is used to launch the vehicle under lower loaded conditions.

A need exists for a transfer case having all-wheel drive capability that can be used in combination with such transmissions.

Preferably the transfer case would not use automatic transmission fluid from the transmission sump or share hydraulic fluid with the transmission.

The transfer case would provide two-wheel drive (2WD) and four-wheel drive 4WD operation with a locked differential and all-wheel drive operation with an open differential.

Preferably the transfer case would not require a controllable hydraulically-actuated clutch, but would produce multiple functional options using a simpler, less costly technique, such as a single displaceable sleeve.

SUMMARY OF THE INVENTION

A transfer case includes a planetary differential including an input, a first output and a second output, a sprocket journalled on the second output, and a sleeve driveably connected to the second output, for (i) releaseably connecting the first output to the sleeve, (ii) releaseably connecting the sprocket to the sleeve, (iii) releaseably connecting the first output and the sprocket to the sleeve, and (iv) disconnecting the sprocket and first output from the sleeve.

The transfer case operates alternately in 2WD, 4WD, AWD and Neutral modes without need for a controllable hydraulically-actuated clutch. All transfer case function options are controlled by a single displaceable sleeve.

The transfer case requires no sharing of hydraulic fluid with the hydraulic system of the transmission.

A vehicle equipped with the transfer case can be towed with all its wheels contacting the ground, i.e., in flat-tow mode, without transmitting wheel rotation to the vehicle's transmission.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first toFIG. 1, a motor vehicle powertrain includes front and rear wheels10,12, a power transmission14for producing multiple forward speed ratios and reverse drive, and a transfer case16. An engine (not shown) transmits power through a torque converter17to the input of transmission14.

When two-wheel-drive (2WD) operation of the powertrain is selected, the transfer case16driveably connects the transmission output to a rear drive shaft18. When four-wheel-drive (4WD) or all-wheel-drive (AWD) operation is selected, the transfer case16directly connects the transmission output concurrently to the front drive shaft20and to rear drive shaft18through a chain drive30.

Shaft18transmits power to a rear wheel differential mechanism22, from which power is transmitted differentially to the rear wheels12through axle shafts24,26, which are contained within a differential housing. The front wheels10are driveably connected to right-hand and left-hand half shafts32,34, to which power is transmitted from the front drive shaft20through a front differential36.

The components of transfer case16include an input40, which is driveably connected to the output of transmission14; a planetary differential42, which split input torque in two equal portions carried by a planet carrier44and by sun gear46; a sprocket48, which is engaged by a drive chain30; a first output50of planetary differential42secured to sun gear46and continually driveably connected to rear driveshaft18; a sleeve52; a rail54; and a fork56, which is secured to rail54for axial displacement with the rail and engages a recess58on sleeve52, thereby allowing the sleeve to rotate relative to the fork and rail.

Differential42further includes a ring gear60, secured to input40; first planet pinions62meshing with ring gear60and supported on carrier44; second planet pinion supported on carrier44and meshing with pinions62and ring gear46. The differential42has a second output represented by carrier44and a sleeve shaft66, which is secured to carrier44.

Sleeve shaft66is formed with external axial spline teeth68, which are in continuous meshing engagement with internal, axial spline teeth70formed on sleeve52.

Sprocket48is journalled on the sleeve shaft66portion of the differential's second output.

Output50includes external, axial spline teeth74formed on the outer cylindrical surface of disc72. Due to axial displacement of sleeve52, spline teeth74mesh with and disengage from internal, axial spline teeth76, formed on an internal cylindrical surface of an annular member78, secured to an axial end of sleeve52. Due to axial displacement of sleeve52, spline teeth74also mesh with and disengage from internal, axial spline teeth80, formed on an internal cylindrical surface of sleeve52.

Sprocket48is formed with external, axial spline teeth82. Due to axial displacement of sleeve52, spline teeth82can mesh with and disengage from internal, axial spline teeth84, formed on an internal cylindrical surface of sleeve52.

Transfer case16operates in 2WD mode in response to movement of fork56to the position shown inFIG. 3. Spline teeth74on disc72of the output50mesh with spline teeth80of sleeve52. Spline teeth68of sleeve shaft66mesh with spline teeth70of sleeve52. Differential42is then locked due to the sun gear46and carrier44being mutually connected at sleeve52. But because sprocket48is not engaged with sleeve52, torque is not transmitted by drive chain30to the front drive shaft20. Therefore, output50transmits all of the torque at input40through locked differential42, rear driveshaft18, rear differential22and shafts24,26to the rear wheels12, which are the primary wheels.

Transfer case16operates in neutral mode when fork56is moved to the position shown inFIG. 4. Because sprocket48is not engaged with sleeve52, no torsional reaction is applied by the front wheels10, through sprocket48, to carrier44. Differential42, therefore, is open due to sun gear46and carrier44being mutually disconnected at sleeve52, due to spline teeth74on disc72of the output50being disengaged from spline teeth80of sleeve52.

Transfer case16operates in AWD mode when fork56is moved to the position shown inFIG. 5. Spline teeth82on sprocket48mesh with spline teeth84of sleeve52. Spline teeth68of sleeve shaft66mesh with spline teeth70of sleeve52. Differential42is then open and transmits approximately one-half of the torque at input40(the secondary wheels) through carrier44, sleeve shaft66, into sleeve52through meshing spline teeth68,70, out of sleeve52to sprocket48through meshing spline teeth82,84, in drive chain30and front axle shaft20to the front wheels10. Similarly, differential42transmits approximately one-half of the torque at input40to the rear wheels10through output50, and sun gear46.

Transfer case16operates in 4WD mode when fork56is moved to the position shown inFIG. 6. Spline teeth74on disc72of the output50mesh with spline teeth76of sleeve52. Spline teeth68of sleeve shaft66mesh with spline teeth70of sleeve52. Differential42is then locked due to sun gear46and carrier44being mutually connected at sleeve52. The front wheels10are driveably connected through front drive shaft20, drive chain30, sprocket48, and meshing spline teeth82,84, to sleeve52. Similarly, the rear wheels12are driveably connected through rear drive shaft18, and meshing spline teeth74,76to sleeve52. Input40is connected thought locked differential42and meshing spline teeth68,70to sleeve52.

A hydraulic or electric actuator90, preferably located in transmission14, is used displace the rail54, fork56and sleeve52among the axial positions that correspond to the selected operating mode of transfer case16.