Locking differential having improved torque capacity

A locking differential for an automotive vehicle including a housing and a differential mechanism supported in the housing. The differential mechanism includes a pair of clutch members disposed in spaced axial relationship with respect to each other wherein each clutch member includes a groove disposed in an opposed inwardly directing face that is adapted to receive a cross pin. Each of the grooves includes a working surface extending laterally relative to each other. Each of the working surfaces defines a screw involute surface such that the cross pin contacts the working surface along a line extending in the direction of the cross pin in the event of differential rotation of an axle half shaft relative to the housing. Alternatively, each of the working surfaces defines a slightly convex surface in one plane such that the cross pin contacts the working surface at a point defined thereon. In another embodiment, the working surface defines a slightly convex surface in two planes such that the cross pin contacts the working surface at a point defined thereon.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, generally, to locking differentials for automotive vehicles, and more specifically to features of a locking differential that result in increased torque capacity and density for a given size of the differential.

2. Description of the Related Art

Locking differentials of the type contemplated by the present invention are employed as a part of a drive train and generally include a pair of clutch members supported for rotation in a housing. A pair of side gears are splined for rotation to corresponding axle half shafts. A clutch mechanism is interposed between the clutch members and the side gears. A cross pin is operatively mounted for rotation with the housing and is received in a pair of opposed grooves formed on the inwardly facing surfaces of the clutch members. In the event of excess differential rotation between the axle half shafts, such as when one tire is supported on a slippery surface, the cross pin acts on the associated clutch member to engage the clutch mechanism thereby coupling the pair of axle half shafts together.

While locking differentials of this type have generally worked for their intended purposes, certain disadvantages remain. More specifically, the size of the components of the differential are often dictated by the amount of torque that can be transmitted thereby. Higher torque requirements typically require larger, more robust components such as the cross pin, clutch members, etc. This design limitation ultimately increases the cost of a differential for the given amount of torque capacity and density required in any application.

Thus, there remains a need in the art for a locking differential that is designed so as to increase its torque capacity and density without the need for increasing the size of the related components, thereby reducing the cost of the differential.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages in the related art in a locking differential for an automotive vehicle that includes a housing and a differential mechanism supported in the housing. The differential mechanism includes a pair of clutch members disposed in spaced axial relationship with respect to one another and operatively supported for rotation with the housing. A pair of side gears is operatively adapted for rotation with a corresponding pair of axle half shafts. A pair of clutch mechanisms is operatively disposed between the corresponding pair of clutch members and the side gears. The clutch members are axially moveable within the housing to engage a respective clutch mechanism to couple the axle half shafts together in the event of a predetermined amount of differential movement between the axle half shafts. Each of the pair of clutch members presents an inwardly directed face. Each face includes a groove disposed in facing relationship with respect to the other. A cross pin is received in the grooves and operatively connected for rotation with the housing. Each of the grooves includes a pair of working surfaces extending laterally relative to each other. In one embodiment of the present invention, the working surfaces define a screw involute surface such that the cross pin contacts the working surfaces along a line extending in the direction of the cross pin in the event of differential rotation of an axle half shaft. In another embodiment of the present invention, the working surfaces define a slightly convex surface in one plane such that the cross pin contacts the working surface at a point defined thereon in the event of differential rotation of one axle half shaft. In still another embodiment of the present invention, the working surfaces define a slightly convex surface in two planes such that the cross pin contacts the working surface at a point defined thereon in the event of differential rotation of one axle half shaft.

In this way, the locking differential of the present invention employs clutch members having working surfaces having screw involute working surfaces that allow for line contact between the cross pin and the working surface; a working surface that may be slightly convex in one plane; or a working surface that may be topologically modified to be slightly convex in two planes that allows for point contact between the cross pin and the working surface. This structure significantly reduces the edge stress generated by the interaction of the cross pin and the working surface and thereby increases the torque density that may be generated through the differential for a given size of the cross pin and clutch member. Accordingly, the present invention reduces the necessity of increasing the size of the related component and by association the cost of the differential for a given torque capacity of the differential.

DETAILED DESCRIPTION

One embodiment of a locking differential of the type contemplated by the present invention is generally indicated at10inFIGS. 1-2. The locking differential10is designed to be employed as a part of a drive train for any number of vehicles having a power plant that is used to provide motive force to the vehicle. Thus, the differential10includes a housing, generally indicated at12. The housing12may support a ring gear14that is designed to be driven in meshing relationship with the pinion gear16fixed to a drive shaft18. The ring gear14, pinion16and driveshaft18are shown in phantom inFIG. 1. The housing12may be composed of a main body20and a cap22that is fixedly mounted to the main body20at a pair of mating annular flange portions24A and24B via bolts26or any other suitable fastening mechanism. The ring gear14may also be mounted to the housing12at the mating flanges24A,24B via the fastener26. Those having ordinary skill in the art will appreciate from the description that follows that the housing may be defined by any conventional structure known in the related art and that the present invention is not limited to a housing defined by a main body and a cap portion. Similarly, the housing12may be driven by any conventional drive mechanism known in the related art and that the invention is not limited to a housing that is driven via a ring gear, pinion, and drive shaft.

The main body20defines a hub28that supports one30of the pair of axle half shafts30,32. Similarly, the cap22defines an opposed hub34that supports the other one32of a pair of axle half shafts. Together, the main body20and cap22of the housing12cooperate to define a cavity36. A differential mechanism, generally indicated at38, is supported in the cavity36defined by the housing12. The differential mechanism38is also illustrated in the exploded view ofFIG. 3and includes a pair of clutch members40disposed in spaced axial relationship with respect to one another. The clutch members40are operatively supported for rotation with the housing12. A pair of side gears42,44is operatively adapted for rotation with a corresponding one of the pair of axle half shafts30,32. To this end, the side gears42,44define splines46on the inner circumference thereof that are matingly received in corresponding splines defined on the axle half shafts30,32. A pair of clutch mechanisms, generally indicated at48and50, is operatively disposed between each corresponding pair of clutch members40and side gears40,42. To this end, the side gears42,44include splines52on the outer circumference thereof. The clutch mechanism48,50includes a plurality of friction disks54that are cooperatively splined to the outer circumference of the side gears42,44and are rotatable therewith. Similarly, each of the pair of clutch members40includes a plurality of splines56formed on the inner circumference thereof. A series of plates58are operatively supported on the splined inner circumference56of the clutch members40and are interleaved between the plurality of friction disks54supported on the side gears42,44. The pair of clutch members40are axially moveable within the housing12to engage a respective clutch mechanism48,50to couple their associated axle half shafts30,32together in the event of a predetermined amount of differential movement between the axle half shafts as will be described in greater detail below. One embodiment of the locking differential of the type contemplated by the present invention may also employ a plurality of biasing members60that are disposed between the clutch members40and receiving in cavities61to urge the clutch members40away from one another.

As best shown inFIGS. 3-5, each of the pair of clutch members40presents an inwardly directed face62disposed in spaced axial relationship to one another. Each of the inwardly directed faces62of the pair of clutch members40includes a groove, generally indicated at64, disposed in facing relationship with respect to the other. A cross pin66is received in the grooves64and is operatively connected for rotation with the housing12. To this end, the differential10may also include a tubular mounting sleeve68(FIGS. 1-2) splined to the inner circumference of the main body20of the housing12. The cross pin66may be fixed to the tubular sleeve at corresponding apertures70formed in the sleeve68for this purpose. However, those having ordinary skill in the art will appreciate from the description set forth herein that the cross pin66may be operatively mounted for rotation with the housing12in any suitable manner.

Referring now specifically toFIGS. 4-5, each of the grooves64is defined by a groove bottom72and a pair of working surfaces74extending laterally relative to one another. The groove bottom72is disposed between and operatively interconnects the pair of working surfaces74. In addition, in one embodiment, the working surfaces extend at an obtuse angle relative to each other. However, those having ordinary skill in the art will appreciate from the description that follows that the grooves64do not necessarily need to define a groove bottom72in order to function in the way intended by the present invention. The working surfaces also define inner and outer radial edges75,77, respectively. In its operative mode, the cross pin66engages the working surfaces74to drive the clutch members40axially outwardly to thereby engage the clutch mechanisms48,50and couple the axle half shafts30,32together as will be described in greater detail below.

More specifically, the locking differential10of the type described above allows for a certain amount of limited slip between the axle half shafts30,32to which it is mounted. However, in an automotive context, for example, when one of the tires is solidly supported and the other one is slipping (such as when one tire is on the pavement and the other is supported on a slippery surface, such as ice) the differential acts to transfer torque from the slipping tire to the solidly supported tire. This occurs when the cross pin66engages the working surfaces74of the groove64disposed on opposite sides of the centerline CLof the groove64to move the associated clutch member40into engagement with an associated clutch mechanism48,50thereby coupling the axle half shafts30,32of the spinning tire to the other solidly supported shaft. In this way, torque is transferred from the slipping tire to the solidly supported tire thereby allowing the vehicle to be driven even though one of the tires is slipping. The opposed working surfaces74that are engaged by the cross pin66in this operational embodiment are shaded as designated at76inFIG. 5and are disposed on opposite sides of a centerline CLbisecting the groove64(FIG. 4).

When there is differential movement of the axle half shafts supported by the locking differential of the type known in the prior art, the cross pin and the working surface of the groove operate to create areas of increased stress at the radial edges of the working surface. These areas of increased stress are illustrated in the arcuately stippled portions indicated at78illustrated inFIG. 5. These areas of increased stress78limit the amount of torque that can be generated for a given size of differential. Thus, where increased torque is required for any given application, the clutch members and cross pins must be increased in size and thickness and may also require additional heat treat and other processes in order to handle the increased torque applied to the differential.

On the other hand, the locking differential10of the present invention employs a groove64with specially designed working surfaces74that are calculated to eliminate or reduce the edge stress at the radial edges of the working surfaces. Thus, a locking differential10employing the specially designed working surfaces of the present invention is capable of transmitting more torque for a given size of differential, thereby reducing the cost of manufacturing the differential.

More specifically, and referring now toFIGS. 6A-6C, one embodiment of the locking differential of the present invention employs working surfaces74that define a screw involute surface representatively designated at80inFIG. 6B. In this case, the cross pin66will contact the screw involute working surface80along a line82extending in the direction of the cross pin66in the event of differential rotation of an axle half shaft relative to the housing12. More specifically, and with continuing reference toFIG. 6A-6C, the screw involute surface80defines an imaginary point A located near the outer radial edge77of the clutch member40adjacent to the groove bottom72and an imaginary point B located near the inner radial edge75of the clutch member40remote from the groove bottom72. The screw involute surface80is slightly convex between the imaginary points A and B such that an imaginary plane P may be defined orthogonal to the working surface74and intersects an imaginary point C at the outer radial edge77of the working surface74. The imaginary plane P defines a line82extending radially across the working surface. In this operative mode, and as noted above with reference toFIG. 4, the cross pin66engages the working surfaces74disposed on opposite sides of the center line illustrated in that figure. The use of screw involute working surfaces80produces line contact between the cross pin66and the working surface74thereby substantially reducing the problem of edge stress generated by the interaction of the cross pin66and the working surfaces74. However, it is also true that, while ideal, screw involute working surfaces are difficult to manufacture. Thus, those having ordinary skill in the art will appreciate that the use of theoretically perfect screw involute working surfaces may not be completely practical in a commercial embodiment of the present invention.

In recognition of this difficulty,FIGS. 7A-7Bdisclose another embodiment of the present invention where like numbers are used to designate like structure and same are increased by100. This embodiment also reduces the edge stress generated between the cross pin66and the working surfaces174but is more feasible to manufacture in a commercial embodiment. More specifically, the working surfaces174defined inFIGS. 7A and 7Bare slightly convex in one plane, such that the cross pin66contacts the working surface at an imaginary point F defined thereon in the event of differential rotation of an axle half shaft relative to the housing. For example, and as illustrated in these figures, the working surface174defines an imaginary point D located near the outer radial edge77of the clutch member40adjacent to the groove bottom72and an imaginary point E located near the inner radial edge77of the clutch member40remote from the groove72. The working surface is slightly convex between the imaginary points D and E such that an imaginary plane P defined orthogonal to the working surface174intersects an imaginary point F on the working surface. The cross pin66establishes point contact between the annular surface of the cross pin66and the working surface174of the clutch member40. In this context, and as best representatively illustrated inFIG. 7B, the radius of convexivity of the working surface174should be as large as possible. A large radius of curvature of the convex working surface174substantially reduces the edge stress on these surfaces.

Another embodiment of the working surface of the locking differential of the present invention is also illustrated inFIGS. 8A and 8Bwhere like numerals are used to designate like structure and where same reference numbers have been increased by200relative to the embodiment illustrated inFIGS. 6A-6C. In this embodiment, the working surfaces274have been topologically modified so that they are slightly convex in two planes. In this embodiment, the cross pin66will contact the working surface at an imaginary point F defined thereon during differential rotation of the clutch member relative to the housing.

In this way, the locking differential of the present invention employs clutch members having working surfaces having screw involute working surfaces that allow for line contact between the cross pin and the working surface; a working surface that may be slightly convex in one plane; or a working surface that may be topologically modified to be slightly convex in two planes that allows for point contact between the cross pin and the working surface. This structure significantly reduces the edge stress generated by the interaction of the cross pin and the working surface and thereby increases the torque density that may be generated through the differential for a given size of the cross pin and clutch member. Accordingly, the present invention reduces the necessity of increasing the size of the related component and by association the cost of the differential for a given torque capacity of the differential.

The invention has been described in great detail in the foregoing specification, and it is believed that various alterations and modifications of the invention will become apparent to those having ordinary skill in the art from a reading and understanding of the specification. It is intended that all such alterations and modifications are included in the invention, insofar as they come within the scope of the appended claims.