Reduced drag front axle shift mechanism

A front axle shift mechanism configured to be operably associated with a front axle housing having a front differential and a first lubricant is provided. The front axle shift mechanism includes a disconnect feature housing defining an inner cavity to house a shifting mechanism configured to selectively provide power to front wheels of the vehicle, the shifting mechanism configured to rotatably couple to the front differential. The inner cavity is configured to receive a second lubricant to facilitate providing lubrication to the first clutch gear and the second clutch gear. The second lubricant is fluidly separate from the first lubricant.

FIELD OF THE INVENTION

The subject invention relates to four wheel drive axle shift mechanisms and, more specifically, to an axle shift mechanism with independent lubrication.

BACKGROUND

Four-wheel drive vehicles provide improved traction on roads such as those covered in snow, ice, and mud. Four-wheel drive vehicles may be provided with an axle shift mechanism to selectively disconnect a secondary driving axle in order to provide a two-wheel drive mode when using four-wheel drive mode is not beneficial. Some four-wheel drive axle shift mechanisms may utilize axle gear lubricant to lubricate the shift mechanism. However, in some low temperature conditions, it may be difficult for the four-wheel drive shift to occur due to drag that may result from the cold, lower viscosity axle gear lube.

SUMMARY OF THE INVENTION

In one aspect, a front axle shift mechanism configured to be operably associated with a front axle housing having a front differential and a first lubricant is provided. The front axle shift mechanism includes a disconnect feature housing defining an inner cavity to house a shifting mechanism configured to selectively provide power to front wheels of the vehicle, the shifting mechanism configured to rotatably couple to the front differential. The inner cavity is configured to receive a second lubricant to facilitate providing lubrication to the first clutch gear and the second clutch gear. The second lubricant is fluidly separate from the first lubricant.

In another aspect, a vehicle is provided. The vehicle includes a body, a front axle housing having a front differential and a first lubricant disposed therein, and a front axle shift mechanism. The front axle shift mechanism includes a disconnect feature housing defining an inner cavity to house a shifting mechanism configured to selectively provide power to front wheels of the vehicle, the shifting mechanism configured to rotatably couple to the front differential. A second lubricant is disposed in the inner cavity to facilitate providing lubrication to the first clutch gear and the second clutch gear. The second lubricant is fluidly separate from the first lubricant.

In yet another aspect, a method of manufacturing a front axle shift mechanism configured to be operably associated with a front axle housing having a front differential and a first lubricant is provided. The method includes providing a disconnect feature housing defining an inner cavity to house a shifting mechanism configured to selectively provide power to front wheels of the vehicle, the shifting mechanism configured to rotatably couple to the front differential, and providing a second lubricant in the inner cavity to facilitate providing lubrication to the shifting mechanism.

DETAILED DESCRIPTION

FIG. 1illustrates a schematic view of an exemplary part-time four-wheel drive vehicle100that generally includes an internal combustion engine102, a transmission104, and a transfer case106to receive drive torque from engine102and transmission104. A transfer case first output member108is drive connected to a rear driveshaft110, which in turn is drivingly connected to a rear differential112. The rear differential112drives rear wheels114in a known manner. A transfer case second output member116is drive connected to a front drive shaft118, which in turn is connected to a front differential gear assembly120disposed in a front axle housing122. Front differential gear assembly120selectively drives front wheel124utilizing a four-wheel drive front axle shift mechanism10.

FIGS. 2 and 3illustrate an exemplary front axle shift mechanism10operably associated with main axle housing122(FIG. 1). Front axle shift mechanism10generally includes a clutch shaft12, a flange14, a disconnect feature housing16, an extension shaft18, and a front axle actuator19assembled thereto. In one embodiment, front axle shift mechanism10is provided as a unitary disconnect assembly configured to couple to front axle housing122.

Clutch shaft12includes a first end20and a second end22. First end20is splined and is configured to couple to front differential gear assembly120. Second end22includes first clutch gear24configured to selectively engage extension shaft18to transmit a rotational force thereto. A clutch collar26is retained for rotation with an axial sliding movement on first clutch gear24. As shown inFIG. 3, clutch shaft12extends through a tube or sleeve28disposed between flange14and disconnect feature housing16.

Flange14is disposed about clutch shaft12and is configured for coupling to front axle housing122. Flange14includes an inner diameter30to receive clutch shaft12, a removable plug32to hold shaft12in place during shipment, and a seal34(FIG. 3) to prevent axle lubrication in front axle housing122from traveling down sleeve28to disconnect feature housing16.

Extension shaft18includes a first end36and a second end38. First end36is splined and is configured to couple to a half shaft126(FIG. 1) coupled to front wheel124. Second end38includes a second clutch gear40for coupling to first clutch gear24, thereby connecting clutch shaft12and extension shaft18for common rotation. In this position, front differential gear assembly120may transfer power from transfer case106to front wheels124.

Disconnect feature housing16includes a first end46, a second end48and an inner cavity50disposed therebetween. First end46includes an inner diameter52to receive clutch shaft second end22, a bearing54, and a seal56(FIG. 3). Bearing54rotatably supports clutch shaft12, and seal56prevents lubricant in cavity50from traveling down sleeve28to front axle housing122. As such, seals34and56prevent mixing of the front axle lubricant and the disconnect feature lubricant such that front axle housing122and disconnect feature housing16include fluidly separate lubrication systems.

Second end48includes an inner diameter58to receive extension shaft second end38, a bearing60, and a seal62(FIG. 3). Bearing60rotatably supports extension shaft18, and seal62prevents lubrication in cavity50from traveling outward toward wheel124.

Inner cavity50houses a disconnect shift system64that includes selectively engageable first clutch gear24, clutch collar26, and second clutch gear40. As described, inner cavity50houses a volume of lubricant for lubricating shift system64and bearings54,60. This is in contrast to some known systems which rely on splashing of the axle lube from a front axle housing for lubrication purposes. Further, in contrast to axle lube, disconnect feature lubrication is a lower viscosity lubricant, which reduces drag under low temperature conditions (e.g., between approximately −20° F. and approximately −40° F.). Moreover, the disconnect feature lubricant reduces shift efforts on a manual transfer case (not shown) by lowering rotating inertia under the low temperature conditions, and reduces axle lube volume in the main sump of the front axle housing122since the axle lube is not required to be directed into sleeve28.

In one embodiment, the disconnect feature lubricant is Automatic Transmission Fluid (ATF). In another embodiment, the disconnect feature lubricant is a lubricant having a Brookfield Viscosity of between 5,000 Cp and 25,000 Cp at −40° F. In yet another embodiment, the disconnect feature lubricant is a lubricant having a Brookfield Viscosity of between approximately 5,000 Cp and approximately 25,000 Cp at −40° F. In one embodiment, the disconnect feature lubricant is a lubricant having a Brookfield Viscosity of between 10,000 Cp and 20,000 Cp at −40° F. In another embodiment, the disconnect feature lubricant is a lubricant having a Brookfield Viscosity of between approximately 10,000 Cp and approximately 20,000 Cp at −40° F. In one embodiment, the disconnect feature lubricant is a lubricant having a Brookfield Viscosity of 15,000 Cp at −40° F. In another embodiment, the disconnect feature lubricant is a lubricant having a Brookfield Viscosity of approximately 15,000 Cp at −40° F. The axle lubricant of front axle housing122may have a Brookfield Viscosity of 60,000 Cp at −40° F.

Front axle actuator19selectively shifts clutch collar26from an uncoupled first position (FIGS. 2 and 3) to a coupled second position (not shown) where clutch collar26couples first clutch gear24for rotation with second clutch gear40, thereby connecting clutch shaft12and extension shaft18for common rotation. As such, disconnect shift system64has a first operating mode for a two-wheel drive operation of vehicle100and a second operating mode for a four-wheel drive operation of vehicle100.

In the first operating mode, shafts12,18are not coupled and rotate independently. In this first operating mode, rolling movement of front wheels124does not drive front differential gear assembly120. In the second operating mode, where front axle actuator19shifts clutch collar26to the second position to couple shafts12and18for co-rotation, front wheels124are operably coupled to engine102.

A method of manufacturing front axle shift mechanism10includes providing clutch shaft12, flange14, disconnect feature housing16, extension shaft18, and front axle actuator19. Clutch shaft12includes first end20and second end22having first clutch gear24and clutch collar26. Flange14may be coupled to front axle housing122and includes sleeve28, bearing32, and seal34disposed within flange inner diameter30. Extension shaft18includes first end36and second end38having second clutch gear40. Disconnect feature housing16defines inner cavity50configured to house first clutch gear24, clutch collar26, and second clutch gear40. Inner cavity50is provided with a lubricant different and separate from axle lubricant in front axle housing122. One or more seals34,56are provided to fluidly separate the inner cavity lubricant and the axle lubricant. Front axle actuator19is operably coupled to clutch collar26to selectively couple first clutch gear24and second clutch gear40.

Described herein are systems and methods for lubricating a front axle shift mechanism. A lower viscosity lubricant is used exclusively within a disconnect feature housing of the front axle shift mechanism, which reduces drag on the front axle shift mechanism, particularly under cold temperature conditions. Further, the system reduces the volume of axle lubrication contained within the main axle housing, which lowers drag on the vehicle and results in better fuel economy.