Planetary gear transmission systems or components – Differential planetary gearing – Spur gear differential
Reexamination Certificate
2000-10-31
2003-10-21
Marmor, Charles A (Department: 3681)
Planetary gear transmission systems or components
Differential planetary gearing
Spur gear differential
C475S252000
Reexamination Certificate
active
06634979
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to differential gear systems used in vehicles and, specifically, to a differential gear system providing adjustable resistance to differential action.
2. Description of the Related Art
As is well known to those skilled in the art, when a vehicle turns a corner, the driven road wheels of the vehicle rotate at different speeds, as the wheel on the inside of the curve travels a shorter distance than the wheel on the outside of the curve. For this reason, the drive shaft from the vehicle engine cannot be coupled directly to a continuous axle that carries the driven road wheels. Instead, the drive shaft must be coupled to a differential gear mechanism that drives two separate half shafts. Each half shaft carries a respective wheel. In this manner the wheels can be driven at different speeds of rotation.
In a vehicle having a conventional differential gear system, the vehicle drive shaft, which forms a connection from the gearbox or transmission case, has a bevel pinion that engages a larger bevel gear wheel called a crown wheel. The crown wheel is secured to a differential casing in which differential pinions are mounted. The differential pinions are rotatably mounted in the casing. When the casing rotates due to rotation of the crown wheel to which it is secured, the differential pinions revolve around the wheels' axis as they are carried by the rotating casing.
When the vehicle is traveling straight ahead, the casing rotates, but the differential pinions do not spin about their individual longitudinal axes. These pinions are engaged with bevel gears that are rigidly connected to the inner ends of the half shafts so that the latter rotate at the same speed. When the vehicle goes around a corner, one half shaft rotates at a slower speed than the other, causing the differential pinions to spin about their respective axes in the casing. The action of the differential pinions retards rotation of the bevel wheel of one half shaft and at the same time accelerates the bevel wheel of the other half shaft.
A disadvantage of such conventional differential mechanisms is that they permit one of the driven wheels to spin excessively if that wheel has less tractive ability than the other wheel, such as occurs under conditions of ice or mud. The total tractive ability of the vehicle is then limited to only one wheel. As the slipping wheel overspins, the differential pinions reactively spin and consequently reduce the torque supplied to the non-slipping wheel.
Several differential mechanisms have been proposed to overcome this disadvantage. One particularly useful design is illustrated and described in European Patent Application No. 84304420.7 to Quaife. This differential gear system includes a casing in which two collinear sun gears are journaled, the casing configured to rotate about the axis of rotation of the vehicle's wheels. Each sun gear has a splined connection to one of the half shafts that are connected to the wheels, such that rotation of a wheel causes likewise rotation of its respective sun gear. Two sets of planetary differential pinions are journaled in cylindrical pockets in the casing, the pockets being parallel to the axis of rotation of the wheels. Each set of pinions is engaged with one of the sun gears, such that the pinions surround the sun gear. Also, each pinion of one set is adjacent to and engaged with two pinions of the other set, such that as one set of pinions rotates in one direction, the other set of pinions rotates in the opposite direction. Collectively, the two sets of engaged differential pinions surround the axis of wheel rotation. The sun gears and the differential pinions have helical teeth. The casing includes end plates that enclose the pinions in the cylindrical packets of the casing. Each of the packets also encloses a thrust plate on the outer axial end of the enclosed differential pinion. The thrust plates are non-rotatably secured with respect to the casing.
This prior art differential mechanism operates as follows: When the vehicle is traveling straight ahead, the casing rotates. This causes the differential pinions to revolve about the half shafts. However, the pinions do not spin about their respective longitudinal axes. Since the differential pinions remain stationary with respect to the casing, the sun gears, which are engaged with the pinions, likewise do not rotate with respect to the casing. Thus, the sun gears, along with their respective half shafts and wheels, rotate at the same speed as the casing. In this manner, rotation of the casing causes rotation of the wheels. When the vehicle travels along a curve, the differential pinions rotate to slightly accelerate the speed of the wheel on the inside of the curve and to slightly decelerate the speed of the wheel on the outside of the curve.
When one wheel slips (for example, due to ice or mud on the road surface), the acceleration of the slipping wheel causes its respective sun gear to accelerate. The helical teeth of the sun gear mesh with the complementary helical teeth of the engaged set of differential pinions, causing the sun gear to be thrust axially inward and the differential pinions to be thrust axially outward against their respective thrust plates. The thrust plates apply a frictional force against the pinions that retards the spinning of the pinions and the slipping wheel. This frictional resistance to differential action prevents to some extent a reduction of torque to the non-slipping wheel.
SUMMARY OF THE INVENTION
It is a principal object and advantage of the present invention to provide a differential gear system in which frictional resistance to differential action can be adjusted to suit the particular needs of the driver and the driving conditions, as may be desired, for example, by racing enthusiasts. This is accomplished by the use of friction pads that are biased against the differential pinions by biasers, such as springs. Adjusters, such as set screws, may be included to permit adjustment of the biasing force of the biasers.
In one aspect, the present invention provides a differential gear mechanism comprising a casing, first and second sun gears, first and second sets of planetary pinions, a friction pad, and a spring. The first and second sun gears are rotatably mounted in the casing and are adapted to be connected to first and second half shafts, respectively, that are connected to road wheels of the vehicle. The first set of planetary pinions are journaled in a first set of pockets defined the casing, and are arranged to surround and mesh with the first sun gear. The second set of planetary pinions are journalled in a second set of pockets defined by the casing, and are arranged to surround and mesh with the second sun gear. The two sets of planetary pinions also mesh with one another. Each pocket for one set of pinions intersects two adjacent pockets for the other set of pinions, whereby each pinion of one set meshes with two adjacent pinions of the other set so that the planetary pinions of the first and second sets mesh with each other in a circle surrounding the sun gears. The friction pad is positioned on the axially facing outer end of at least one of the planetary pinions, and is biased against the planetary pinion by the spring. Additionally, a spring adjuster may be provided, the spring adjuster being configured to permit adjustment of the spring force applied by the spring onto the friction pad. The sun gears and planetary pinions have helical teeth.
In another aspect, the present invention provides a differential gear system for a vehicle, comprising a casing, first and second sun gears, first and second planetary pinions, first and second friction pads, and first and second springs. The casing is configured to rotate about a wheel axis of rotation of a pair of wheels of the vehicle. The first and second sun gears are rotatably mounted in the casing and are adapted to be connected to first and second half shafts, respectively, that are connected to ro
Ho Ha
Knobbe Martens Olson & Bear LLP
Marmor Charles A
Quaife Michael John
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