Selectable grounded gear linear actuation

A power transfer mechanism includes a shift mechanism translating a shift sleeve to a first position where an input shaft is directly drivingly coupled to a first output shaft and to a second position where a reduced speed drive ratio connection exists between the input shaft and the first output shaft as well as the input shaft and a second output shaft via a first planetary gearset. The shift system includes a second planetary gearset having a planet gear fixed for rotation with a lead screw threadingly engaged with the shift sleeve. Rotation of the planet gear axially translates the shift sleeve. A first clamp arm restricts rotation of one member of the second planetary gearset to cause rotation of the planet gear in a first direction. A second clamp arm restricts rotation of another member of the planetary gearset to rotate the planet gear in an opposite direction.

FIELD

The present disclosure relates generally to a power transfer mechanism used in a four-wheel drive vehicle. More particularly, a shift mechanism includes a linear actuator driven by a planetary gearset equipped with selective grounded members.

BACKGROUND

Demand continues to increase for four-wheel drive vehicles based on the enhanced on-road 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 a primary driveline for establishing a two-wheel drive mode. The transfer case may be 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 may include 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, a sophisticated automatically-actuated multi-plate clutch for providing an “on-demand” four-wheel drive mode, or some other variant.

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. An example of a 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.

Due to the cost and complexity associated with such actively-controlled, on-demand clutch control systems, recent efforts have been directed to constructing simplified transfer cases that provide dedicated operating modes without incorporating multiple friction plate clutches and the associated actuators. It may be beneficial to continue to develop transfer cases that do not require large electric actuator motors or hydraulic pumps but instead take advantage of the kinetic energy of the vehicle to complete a shift. In addition, it may be desirable to disconnect various power transfer components from the load path during certain modes of operation to increase the fuel efficiency of the vehicle.

SUMMARY

A power transfer mechanism includes an input shaft and first and second output shafts. A shift mechanism translates a shift sleeve to a first position where the input shaft is drivingly coupled to the first output shaft in a direct drive ratio connection and to a second position where a reduced speed drive ratio connection exists between the input shaft and the first output shaft as well as the input shaft and the second output shaft via a first planetary gearset. The shift system includes a second planetary gearset having a planet gear fixed for rotation with a lead screw threadingly engaged with the shift sleeve. Rotation of the planet gear axially translates the shift sleeve. The shift system includes a first clamp arm to restrict rotation of one member of the second planetary gearset to cause rotation of the planet gear in a first direction. A second clamp arm restricts rotation of another member of the planetary gearset to rotate the planet gear in an opposite direction.

DETAILED DESCRIPTION

Referring now toFIG. 1, a drive system10for a four-wheel drive motor vehicle is shown to include a power source, such as an engine12, which drives a conventional transmission14of either the manually-shifted or automatic type. The output shaft of transmission14drives an input member of a transfer case16which, in turn, delivers drive torque to a primary output shaft18that is operably connected to a primary driveline20. Primary driveline20includes an axle assembly22having a differential24driving a pair of wheel assemblies26via axleshafts28, and a drive shaft30connected between primary output shaft18and differential24.

Transfer case16further includes a secondary output shaft32that is operably connected to a secondary driveline34. Secondary driveline34includes an axle assembly36having a differential38driving a pair of wheel assemblies40via axleshafts42, and a driveshaft44connected between secondary output shaft32and differential38.

Drive system10also includes an electronic controller46which receives input data from various vehicle sensors47and a mode selector48. Controller46uses the input data from sensors47and mode selector48to generate control signals used to actuate one or more controllable systems associated with transfer case16. According to the arrangement shown, primary driveline20is the rear driveline of a rear wheel drive vehicle while secondary driveline34is its front driveline. Drive torque is typically supplied to rear driveline20and is only transferred to front driveline34when mode selector48signals operation in one of a four-wheel drive or a four-wheel lock mode. However, it will be understood that the teachings of the present disclosure could easily be adapted for use in a front wheel drive vehicle in which the front driveline would be designated as the primary driveline.

Referring primarily toFIG. 2, transfer case16is shown to generally include an input shaft50, rear output shaft18, a planetary reduction gearset52, a front output shaft32, a transfer assembly56, and a shift system60, all of which are mounted with a housing assembly62. Input shaft50is adapted for connection to the output shaft of transmission14. Planetary gearset52includes a sun gear64, a ring gear66non-rotatably fixed to housing assembly62, and a plurality of planet gears68rotatably supported on a planet carrier70.

Transfer assembly56includes a drive sprocket76fixed for rotation with planet carrier70. A driven sprocket78is fixed for rotation with front output shaft32. A flexible drive member such as a chain80drivingly interconnects drive sprocket76and driven sprocket78.

Shift system60includes a first sleeve86, a second sleeve88and a third sleeve90axially translatable between a high-range (H) position, a high lock (HL) position, a neutral (N) position, and a low-range (L) position. In the H position, clutch teeth94on third sleeve90engage clutch teeth96on input shaft50and clutch teeth98of rear output shaft18to establish a direct ratio drive connection between input shaft50and rear output shaft18. When shift system60operates in the H mode, torque is not transferred to front output shaft32.

To provide the HL mode, each of first, second and third range sleeves86,88and90are translated to new positions. In particular, third sleeve90remains drivingly engaged with input shaft50and rear output shaft18. Second sleeve88includes a plurality of clutch teeth102engaged with clutch teeth98of rear output shaft18. Second sleeve88is fixed for rotation with third sleeve90via rear output shaft clutch teeth98but remains axially moveable relative thereto. Second sleeve88is also in a splined connection to first sleeve86. Planet carrier70includes lugs104axially extending toward rear output shaft18that are fixed for rotation with first sleeve86. In the high lock (HL) mode of operation, input shaft50, rear output shaft18, planet carrier70and drive sprocket76rotate at the same speed. Front output shaft32is also continuously driven based on the drive connection between chain80and driven sprocket78.

In the N position, third sleeve90is disengaged from rear output shaft18. Torque is not transferred from input shaft50to either rear output shaft18or front output shaft32. In the L position, a set of clutch teeth108formed on third sleeve90meshingly engage clutch teeth110formed on sun gear64. Reduced speed output from planetary gearset52is provided to drive sprocket76via planet carrier70as well as rear output shaft18via lugs104, first sleeve86and second sleeve88.

Shift system60includes a planetary gearset120including a ring gear122, a sun gear124and a pinion gear126. Pinion gear126is rotatably supported within planet carrier70. A drive screw130is integrally formed with and fixed for rotation to pinion gear126. Drive screw130is threadingly engaged with first sleeve86at a threaded aperture132. Rotation of drive screw130axially translates first sleeve86. Drive screw130may be rotated in either direction to axially translate first sleeve86in either direction.

Shift system60also includes a grounding mechanism140for selectively restricting rotation of ring gear122or sun gear124. When ring gear122is restricted from rotation, pinion gear126rotates in a first direction to translate first sleeve86in a first direction. When ring gear122is free to rotate and sun gear124is restricted from rotation, pinion gear126rotates in the opposite direction. First sleeve86translates in an opposite direction.

A first brake drum144is fixed for rotation with ring gear122. A second brake drum146is fixed for rotation with sun gear124. A first clamp arm148includes a first friction surface150for selective engagement with first brake drum144. In similar fashion, a second clamp arm154includes a second friction surface156selectively engageable with second brake drum146. First clamp arm148and second clamp arm154are biased toward a position where friction surfaces150and156are clear of brake drums144,146. A biasing member such as spring160may be associated with first clamp arm148and second clamp arm154. More than one spring may provide the desired function.

An actuation arm164is fixed for rotation with a dual lobe cam166. A first cam lobe168engages a surface170of first clamp arm148. A second cam lobe172is axially offset from first cam lobe168and is positioned in contact with a surface174of second clamp arm154. First cam lobe168and second cam lobe172are circumferentially clocked at different positions such that rotation of actuation arm164in a clockwise direction when viewed inFIG. 3engages first cam lobe168with first clamp arm148but not second cam lobe172with second clamp arm154. Rotation of actuation arm164in the clockwise direction causes first cam lobe168to drive first clamp arm148in a downward direction to engage first friction surface150with first brake drum144. Second cam lobe172does not cause second clamp arm154to move during clockwise rotation of actuation arm164. Conversely, rotation of actuation arm164in a counter-clockwise direction causes second cam lobe172to drive second clamp arm154downwardly and engage second friction surface156with second brake drum146. First cam lobe168does not drive first clamp arm148into contact with first brake drum144when actuation arm164rotates in the counter-clockwise direction.

A first solenoid178is drivingly coupled to actuation arm164to urge the actuation arm in one of a clockwise or counter-clockwise direction. A second solenoid180is drivingly coupled to actuation arm164to urge actuation arm164in the other of the clockwise or counter-clockwise directions. Controller46is operable to selectively energize either first solenoid178or second solenoid180to rotate actuation arm164in one of the clockwise or counter-clockwise direction. Depending on the rotation induced, ring gear122or sun gear124will be restricted from rotation. During vehicle movement, members of planetary gearset120are driven causing pinion gear126and drive screw130to rotate thereby translating first sleeve86.

FIGS. 4 and 5depict an alternate shift system60a. Shift system60ais substantially similar to shift system60. As such, similar elements will be identified with like reference numerals including an “a” suffix. Shift system60aincorporates a worm gear assembly200including a worm shaft202and a sector gear204in lieu of solenoids178,180. Worm shaft202includes gear teeth206meshingly engaged with gear teeth208of sector gear204. Sector gear204is fixed to a first cam lobe168aand a second cam lobe172a. An electric motor (not shown) may be drivingly coupled to worm shaft202via a socket210. The electric motor may be controlled to rotate in a clockwise or a counter-clockwise direction to rotate sector gear204in either a clockwise or counter-clockwise direction. The remaining operation of shift system60ais substantially similar to shift system60.