Motor vehicles – Having four wheels driven – With differential means for driving two wheel sets at...
Reexamination Certificate
2002-07-25
2004-08-03
Morris, Lesley D. (Department: 3611)
Motor vehicles
Having four wheels driven
With differential means for driving two wheel sets at...
Reexamination Certificate
active
06769506
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an all wheel drive system for a motor vehicle and more specifically, to an all wheel drive system including a pair of front halfshaft assemblies, a power take-off unit, a first propshaft assembly, a second propshaft assembly, a means for controlling torque transmission from the front halfshaft assemblies to the rear halfshaft assemblies, a rear differential, a pair of rear halfshaft assemblies and a torque arm mounting system.
BACKGROUND ART
There are generally four (4) main types of automotive driveline systems. More specifically, there exists a full-time front wheel drive system, a full-time rear wheel drive system, a part-time four wheel drive system, and an all wheel drive system. Most commonly, the systems are distinguished by the delivery of power to different combinations of drive wheels, i.e., front drive wheels, rear drive wheels or some combination thereof. In addition to delivering power to a particular combination of drive wheels, most drive systems permit the respectively driven wheels to rotate at different speeds. For example, the outside wheels must rotate faster than the inside drive wheels, and the front wheels must normally rotate faster than the rear drive wheels while driving in a corner.
Often, the inside and outside drive wheels of a two wheel drive system are connected to a differential mechanism which permits the opposite drive wheels to rotate at different speeds while delivering an approximately equal amounts of drive torque to each. Delivering approximately equal amount of torque to the drive wheels independently of the rotational speed sometimes significantly limits the total amount of torque which can be delivered to the drive wheels when one of the drive wheels loses traction. For example, if either drive wheel does not have sufficient traction to sustain its portion of the drive torque, the amount of drive torque which can be delivered to the other drive wheel is similarly reduced.
In an attempt to overcome this problem, there are certain modifications to differential performance which support unequal distributions of torque between the drive wheels. The unequal distributions of torque are supported by resisting any differential rotation between drive wheels. A limited slip differential modifies a conventional differential by including a frictional clutch mechanism which resists any relative rotation between the drive wheels. Unequal torque distribution between drive wheels is supported by sacrificing some of the differential capacity to support unequal rotational speeds between the drive wheels during cornering.
Recently, all wheel drive vehicles have been gaining popularity as a way to enhance traction capability. Instead of dividing drive power between only two wheels of a vehicle either in the front or the rear, all wheel drive vehicles divide power between all four wheels. As a result, each wheel is required to support a smaller portion of the total drive torque. However, in addition to delivering power to both the front and rear drive axle, all wheel drives must also permit the two axles to rotate at different speeds. Accordingly, driveshafts to the front and rear axles are often interconnected by a differential mechanism which permits the front and rear drive axles to rotate at different speeds while delivering approximately equal amounts of torque. Part-time four wheel drive systems permit a vehicle operator to selectively connect a second drive axle to the vehicle driveline when adverse traction conditions are encountered. It should be noted however, that if both front and rear axles are permanently interconnected by a differential mechanism, more power is expended by the drivetrain delivering power to two drive axles in comparison to delivering power to only one of the axles. Thus, adequate traction is available for a single pair of drive wheels to support the delivery of drive power and the further division of drive power among more than two wheels is not necessary. Significant power losses and reduced gas mileage sometimes occur as a result of the unnecessary transmission of drive power to additional wheels.
Part-time four wheel drive systems rely on operator judgment to select between two and four wheel drive modes. Driveshafts to the front and rear drive axles are generally coupled together in the four wheel drive mode, thereby preventing the two axles from rotating at different speeds. The drive wheels of one or the other axles tend to skid in response to courses of travel which require, the front and rear axles to rotate at different speeds. Accordingly, significant power losses occur in the four wheel drive mode from the tendency of one of the axles to brake the vehicle. Power is delivered to either the front or rear axle depending on whichever axle is required to rotate slower to maintain traction. This makes for unpredictable changes in vehicle handling characteristics by switching between effective front or rear wheel drive. Further, part-time four wheel drive vehicles experience the same loss of traction as two wheel drive vehicles until the four wheel drive mode is engaged.
It is also known in the art to provide a conventional differential interconnecting front and rear drive axles with a limited slip differential to further enhance traction capabilities of all wheel drive vehicles. The limited slip differential supports unequal distributions of torque between drive axles, but it also resist relative rotation between the axles. Accordingly, the same power losses occur from permanently driving an additional axle, and drive torque is unpredictably divided between the front and rear axles in response to situations requiring the drive axles to rotate at different speeds.
U.S. Pat. No. 5,782,328 (“the 328 patent”), to Warn Industries, Inc. describes the use of a bi-directional clutch in combination with a transfer case. More specifically, the '328 patent describes a transfer case for a vehicle having two output shafts, a gear reduction assembly, a coupling mechanism and an overrunning roller clutch for selectively producing driving of one shaft only or both shafts concurrently. The coupling mechanism selectively couples one output shaft to either (1) an input shaft, (2) the gear reduction assembly, or (3) a neutral position. The overrunning clutch has an inner race, and outer race, and rollers located between the races. Drag shoes are positioned to frictionally slide on a drag surface of a selectively grounded member to retard the rollers. A resilient band urges the drag shoes against the drag surface. When the drag shoes rotate at a sufficient speed they disengage from the drag surface so as to provide no force to retard the rollers. When the ground member is grounded it provides the drag surface for the drag shoes. When the ground member is ungrounded it is free to rotate and the drag shoes do not provide a drag force to bias the rollers. A latch may be coupled to the inner race to engage a roller cage to prevent high speed lock-up. A drag ring is located inside the outer race and provides a drag force on the rollers to advance the rollers when it is desired, e.g., when front wheel compression braking is advantageous. An actuator assembly is provided with a variable speed drive for shifting the transfer case between modes of operation.
U.S. Pat. No. 5,195,604, also to Warn Industries, Inc., describes a bi-directional clutch for use with a braking system. More specifically, the '604 patent describes a clutch mechanism for a drive train of a four-wheel drive vehicle for controlling the application of braking power between the front and rear wheels as applied through the drive train. A driving shaft is connected to a driven shaft through a roller clutch assembly and the driven shaft is coupled to a wheel set equipped with anti-lock brakes. The driving shaft has a drive cam race and a driven shaft has a cylindrical race. A cage carries the clutch rollers and is provided with drag shoes biased against a fixed drag ring. The rollers captured by the cage continuously drag ag
Gassmann Theodore
Peura Brent
Dinnin & Dunn P.C.
GKN Automotive Inc.
Morris Lesley D.
Nylander Mick A.
Royal, Jr. Paul
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