Limited-slip differential assembly with partially frustoconical locking tongues

Abstract

Limited-slip differential assembly (12), comprising: a differential housing (60) with a first housing element (74) and a second housing element (76) that work together to define a cavity (66), wherein the first housing element (74) has a first end wall (68); a differential gear (62) received in the cavity (66), wherein the differential gear (62) has a first side gear (80); and A locking mechanism (64) for selectively locking the first side gear (80) to the differential housing (60) for common rotation, the locking mechanism (64) comprising a plurality of locking openings (90), a first locking claw (92) and a second locking claw (94), the locking openings (90) being formed in the first end wall (68), the first locking claw (92) comprising a set of first claw teeth (110) that are rigidly coupled to the first side gear (80), the second locking claw (94) comprising an annular body (118), a set of second claw teeth (120) and a plurality of locking tongues (122), the set of second claw teeth (120) extending from the annular body (118) and configured to engage with the set of first claw teeth (110) to provide relative locking. to prevent rotation between the first and second locking claw (92, 94),wherein the locking tongues (122) extend radially outwards from the ring body (118) and are received in the locking openings (90), wherein the second locking claw (94) is movable along an axis (54) between a first position in which the set of second claw teeth (120) is disengaged from the set of first claw teeth (110) to allow relative rotation between the first side gear (80) and the differential housing (60), and a second position in which the set of second claw teeth (120) engages with the set of first claw teeth (110) to prevent relative rotation between the first side gear (80) and the differential housing (60); wherein the locking openings (90) have a first locking surface (100) which is at least partially frustoconical in shape, and wherein the locking tongues (122) define a second locking surface (130) which is configured to engage appropriately with the first locking surface (100).

Description

AREA

[0001] The present disclosure relates to a limited-slip differential assembly, a method of forming a limited-slip differential assembly, and an axle assembly. BACKGROUND

[0002] This section provides background information related to the present disclosure that may not necessarily constitute prior art.

[0003] Various types of differential assemblies are known in the art for transmitting rotational power from an engine train to a pair of vehicle wheels. Typically, a differential assembly includes a differential case and a differential gear having a pair of side gears driven by the differential case. One type of differential assembly is known as a limited-slip differential assembly and is configured to selectively lock one or both of the side gears of the differential gear to the differential case for common rotation about a rotational axis. Typically, the limited-slip differential assembly includes a locking dog non-rotatably but slidably mounted to the differential case for movement into a position to engage one of the side gears to prevent rotation of the side gear relative to the differential case.Although this configuration is well suited for its intended purpose, this type of limited-slip differential assembly still has room for improvement.

[0004] Limited-slip differential assemblies are known, for example, from WO 2014 / 116 802 A1, US 5 890 989 A and US 2010 / 0 311 533 A1. SUMMARY

[0005] An object of the present invention is to improve the limited-slip differential assemblies known from the prior art with a displaceable locking claw as described above.

[0006] The stated object is achieved by a limited-slip differential assembly having the features of patent claim 1. Furthermore, the object is achieved by a method for forming a limited-slip differential assembly having the features of patent claim 6, as well as an axle assembly having the features of patent claim 10. Further developments of the limited-slip differential assembly, the method, and the axle assembly are the subject of the subclaims.

[0007] In one form, the present disclosure provides a limited-slip differential assembly including a differential case, a differential gear, and a locking mechanism. The differential case has a first case member and a second case member that cooperate to define a cavity. The first case member has a first end wall 68. The differential gear is received within the cavity and has a first side gear. The locking mechanism has a plurality of locking openings, a first locking claw, and a second locking claw. The locking openings are formed in the first end wall 68. The first locking claw has a set of first claw teeth fixedly coupled to the first side gear. The second locking claw has an annular body, a set of second claw teeth, and a plurality of locking tongues.The set of second dog teeth extends from the ring body and is configured to engage the set of first dog teeth to prevent relative rotation between the first and second locking dogs. The locking tabs extend radially outward from the ring body and are received in the locking openings. The second locking dog is movable along an axis between a first position in which the set of second dog teeth is disengaged from the set of first dog teeth to permit relative rotation between the first side gear and the differential case, and a second position in which the set of second dog teeth engages the set of first dog teeth to prevent relative rotation between the first side gear and the differential case. The locking openings have a first locking surface that is at least partially frustoconically shaped.The locking surfaces define a second locking surface configured to matingly engage the first locking surface.

[0008] In another form, the present disclosure provides a method of forming a limited-slip differential assembly. The method includes: providing a first housing member configured to be rotatable about a rotational axis, the first housing member having a plurality of locking openings, each of the locking openings defining a first locking surface having a frustoconical shape;Installing a locking claw on the first housing member, the locking claw having a body, a set of first claw teeth, and a plurality of locking tabs, the set of first claw teeth extending axially from the body, the locking tabs extending radially from the body and received in the locking openings, the locking tabs defining a second locking surface and being received in the locking openings, at least a portion of the second locking surface being frustoconically shaped and configured to matingly engage the first locking surface; and installing a differential gear on the first housing member, the differential gear having a side gear with a set of second claw teeth configured to selectively matingly engage the set of first claw teeth.

[0009] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. DRAWINGS Fig. 1 is a schematic illustration of a vehicle having a rear axle assembly with an exemplary limited-slip differential assembly constructed in accordance with the teachings of the present disclosure; Fig. 2 is a perspective view of the rear axle assembly of Fig. 1; Fig. 3 is an exploded perspective view of a portion of the rear axle assembly illustrating the limited-slip differential assembly in detail; Fig. 4 is a longitudinal sectional view of the limited-slip differential assembly; Fig. 5 is a longitudinal sectional view of a portion of the limited-slip differential assembly, illustrating a first housing member in detail; Fig. 6 is a perspective, partially cutaway view of the first housing member illustrating locking apertures formed in the first housing member; Fig. 7 is a side view of a portion of the limited-slip differential assembly illustrating a second locking pawl in detail; Fig. 8 is a perspective view of a portion of the second locking claw, illustrating a locking tongue formed on a ring body of the second locking claw; Fig. 9 is a sectional view of a portion of the limited-slip differential assembly illustrating contact between a first locking surface formed on the differential case and a second locking surface formed on the locking tab of the second locking pawl.

[0010] Corresponding reference numerals indicate corresponding parts in the several views of the drawings. DETAILED DESCRIPTION

[0011] Exemplary embodiments will now be described more fully with reference to the accompanying drawings.

[0012] With reference to Fig. 1 of the drawings, a vehicle 8 is schematically illustrated as having a rear axle assembly 10 with a limited-slip differential assembly 12 constructed in accordance with the teachings of the present disclosure. The vehicle 8 is a four-wheel drive vehicle having a powertrain 14 including an engine 16 and a transmission 18 that provides rotational power to a drivetrain 20 including a transfer case 22, the rear axle assembly 10, and a front axle assembly 24. Rotational power may be transmitted from the transfer case 22 to the rear axle assembly 10 and the front axle assembly 24 via rear and front propeller shafts 26 and 28, respectively. The configuration of the front axle assembly 24 may be generally similar to that of the rear axle assembly 10, and as such, a discussion of the rear axle assembly 10 for the front axle assembly 24 is sufficient.

[0013] In Fig. 2, the rear axle assembly 10 is illustrated, which includes an axle housing assembly 30, a pinion gear 32, a ring gear 34, the limited-slip differential assembly 12, and a pair of axle shafts 36. The axle housing assembly 30 may be any type of housing assembly, such as a banjo-type axle housing assembly, but in the particular example provided, the axle housing assembly 30 is a Salisbury-type axle housing assembly having a carrier housing 40 and a pair of axle tubes 42 coupled to the carrier housing 40 in a conventional and known manner. The carrier housing 40 may define a cavity 44 into which the limited-slip differential assembly 12 is received.

[0014] The drive pinion 32 may be attached to the support housing 40 for rotation about a first axis 50. The drive pinion 32 may include a bevel gear 52 that may be disposed within the cavity 44. The ring gear 34 may be received within the cavity 44 and rotatable about a second axis 54, which may be transverse or generally perpendicular to the first axis 50. The ring gear 34 may be in meshing engagement with the bevel gear 52.

[0015] With additional reference to Fig. 3, the limited-slip differential assembly 12 may include a differential case 60, a differential gear 62, and a locking mechanism 64. The differential case 60 may be formed as one or more discrete components and may define a differential cavity 66 that may be bounded on opposite sides by first and second end walls 68 and 70, respectively. In the particular example provided, the differential case 60 is an assembly formed from first and second case members 74 and 76 that are bolted together and to the ring gear 34. The differential case 60 may be mounted to the axle housing assembly 30 for rotation about a second axis 54, which may be transverse or perpendicular to the first axis 50. The differential gear 62 may be any type of gearing capable of receiving rotational power from the differential case 60 and outputting rotational power to the axle shafts 36.In the particular example provided, the differential gear 62 includes a bevel gear arrangement (i.e., two or more bevel pinions 78 meshing with first and second (bevel) side gears 80 and 82), but it should be understood that other types of gear arrangements, such as spur or helical gear arrangements, could alternatively be used. The differential gear 62 may include a pair of output members, i.e., the first and second side gears 80 and 82, which may be drivingly coupled to the axle shafts 36 in a conventional manner.

[0016] With reference to the Fig. 3 and Fig. 4, the locking mechanism 64 may include a plurality of locking openings 90, a first locking claw 92, a second locking claw 94, and an actuator 96.

[0017] How best to Fig. 5 and Fig. 6, the locking openings 90 may be formed in the first end wall 68 and may define a first locking surface 100 that is at least partially frustoconically shaped. Each of the locking openings 90 may be formed by a rotating cutting tool 102, such as an end mill, a drill, or a reamer, when the rotating cutting tool 102 is inserted into the first housing member 74 along an axis A that is parallel to the second axis 54. In the particular example provided, all of the locking openings 90 extend completely through the first end wall 68, but those skilled in the art will understand that some or all of the locking openings 90 could be formed in a blind manner to be bounded on one side by the first end wall 68.

[0018] With further reference to the Fig. 3 and Fig. 4, the first locking claw 92 includes a set of first claw teeth 110 that are fixedly coupled to the first side gear 80. The first claw teeth 110 may be disposed on an outboard side surface of the first side gear 80 and may be circumferentially spaced about the second axis 54.

[0019] The second locking claw 94 may include an annular body 118, a set of second claw teeth 120, and a plurality of locking tabs 122. The set of second claw teeth 120 may extend from the annular body 118 and may be configured to engage the set of first claw teeth 110 to prevent relative rotation between the first and second locking claws 92 and 94. The locking tabs 122 may be fixedly coupled to the annular body 118 and may extend radially outward therefrom. Each of the locking tabs 122 may be received in a corresponding one of the locking openings 90. The locking tabs 122 and the locking openings 90 can cooperate to limit rotation of the second locking claw 94 relative to the differential case 60 while allowing movement of the second locking claw 94 along the second axis 54 relative to the differential case 60.The second locking claw 94 is movable along the second axis 54 between a first position in which the set of second dog teeth 120 is disengaged from the set of first dog teeth 110 to permit relative rotation between the first side gear 80 and the differential case 60, and a second position in which the set of second dog teeth 120 engages the set of first dog teeth 110 to prevent relative rotation between the first side gear 80 and the differential case 60.

[0020] With reference to the Fig. 7-9, each of the locking tabs 122 may define a second locking surface 130 that is at least partially frustoconically shaped in a manner configured to mate with the first locking surface 100. Generally, the locking apertures 90 may be configured slightly larger than the locking tabs 122 to allow a relatively small amount of rotation of the second locking claw 94 about the second axis 54 relative to the differential case 60 over at least a portion of the stroke or travel of the second locking claw 94 that includes the second position of the second locking claw 94.

[0021] With further reference to the Fig. 3 and Fig. 4, the actuator 96 may be any type of device that can be used to selectively translate the second locking pawl 94 along the second axis 54. Actuators for translating a component of a locking mechanism relative to a differential case are known in the art and include actuators described in patents US 6,083,134 A, US 6,460,677 B1, US 6,958,030 B2, US 7,211,020 B2, US 7,325,664 B2, US 7,399,248 B2, and US 7,425,185 B2. In the particular example provided, the actuator 96 includes a ring magnet 140, a pressure plate 142, and a return spring 144. The ring magnet 140 may be attached to the differential case 60 in a manner that allows rotation of the differential case 60 relative to the ring magnet 140, but limits movement of the ring magnet 140 along the second axis 54 in a direction away from the second locking pawl 94.The ring magnet 140 may include an electromagnetic coil 150 and a ring plunger 152 that can be selectively moved along the second axis 54 in response to energization of the electromagnetic coil 150. The pressure plate 142 may be fixedly coupled to the second locking claw 94. In the particular example provided, the pressure plate 142 is formed from a plastic material that is overmolded (i.e., cohesively bonded) over the second locking claw 94. The pressure plate 142 may include a plurality of legs 158 that may extend from the second locking claw 94 on a side opposite the set of second claw teeth 120. Each of the legs 158 may extend into a corresponding one of the locking openings 90 and may abut a corresponding one of the locking tongues 122.The return spring 144 may be configured to bias the second locking claw 94 away from the first locking claw 92 such that the set of second claw teeth 120 is normally disengaged from the set of first claw teeth 110. In the particular example provided, the return spring 144 is disposed between the first and second locking claws 92 and 94.

[0022] The limited-slip differential assembly 12 is operable in a first mode in which the actuator 96 places the second locking pawl 94 in the first position so that the set of second dog teeth 120 is disengaged from the set of first dog teeth 110. In this mode, the first side gear 80 is allowed to rotate relative to the differential case 60, so that the limited-slip differential assembly 12 functions as an open differential, allowing speed differential between the first and second side gears 80 and 82.

[0023] The limited-slip differential assembly 12 can also be operated in a second mode in which the actuator 96 places the second locking pawl 94 in the second position so that the set of second dog teeth 120 engages the set of first dog teeth 110. In this mode, the first side gear 80 is locked to the differential case 60 for common rotation, so that the limited-slip differential assembly 12, operating as a locked differential, does not allow a speed difference between the first and second side gears 80 and 82.

[0024] With reference to the Fig. 4 and Fig. 9, the transmission of torque through the sets of first and second dog teeth 110 and 120 may tend to drive the second locking dog 94 along the second axis 54 away from the first locking dog 92, which may tend to reduce the amount of contact between the sets of first and second dog teeth 110 and 120, particularly if the set of first dog teeth 110 is end-formed via forging to be somewhat tapered. The sizing and generally frusto-conical configuration of the first and second locking surfaces 100 and 130 allow limited rotation of the second locking dog 94 relative to the differential case 60 while transmitting torque between the second locking dog 94 and the differential case 60.Furthermore, the generally frustoconical configuration of the first and second locking surfaces 100 and 130 cooperate to generate a force on the locking tabs 122 tending to move the second locking claw 94 along the second axis toward the first locking claw 92. Those skilled in the art will understand that the first and second locking surfaces 100 and 130 may be profiled or tapered in a desired manner so that a magnitude of the portion of the force directed along the second axis 54 can be tailored in a desired manner. For example, a relatively smaller cone angle (used to create the first and second locking surfaces 100 and 130) would generate force with an axially directed component that would be relatively lower in magnitude, whereas a relatively larger cone angle would generate a force with an axially directed component that would be relatively higher in magnitude.In the particular example provided, the cone angle was selected to produce a force having an axially directed component with a magnitude approximately equal to the force generated by the meshing of the first and second dog teeth 110 and 120 (to drive the second locking dog 94 away from the first locking dog 92) when rotational force of a predetermined magnitude and a predetermined rotational direction is transmitted between the first and second locking dogs 92 and 94. Configuring the differential case 60 and the second locking dog 94 in this manner is advantageous in that the sets of first and second dog teeth 110 and 120 can be formed without an undercut. For example, the set of second dog teeth 120 can be formed such that the sides of each tooth can lie in a pair of parallel planes that can be parallel to the second axis 54.A suitable method for forming the set of second claw teeth 120 in this manner includes fine blanking. In this regard, the second locking claw 94 could be formed almost entirely by fine blanking, and an additional operation such as milling or coining could be used to form the second locking surface 100.

[0025] With further reference to the Fig. 7 to 9, a notch 164 may be formed in each of the locking tabs 122 to improve the mechanical connection between the locking tabs 122 and the pressure plate 142 in cases where the pressure plate 142 is overmolded over the locking tabs 122.

Claims

[1] Limited-slip differential assembly (12) comprising: a differential case (60) having a first case member (74) and a second case member (76) cooperating to define a cavity (66), the first case member (74) having a first end wall (68); a differential gear (62) received in the cavity (66), the differential gear (62) having a first side gear (80); and a locking mechanism (64) for selectively locking the first side gear (80) to the differential case (60) for common rotation, the locking mechanism (64) comprising a plurality of locking openings (90), a first locking claw (92), and a second locking claw (94), the locking openings (90) being formed in the first end wall (68), the first locking claw (92) comprising a set of first claw teeth (110) fixedly coupled to the first side gear (80), the second locking claw (94) having an annular body (118), a set of second claw teeth (120), and a plurality of locking tongues (122), the set of second claw teeth (120) extending from the annular body (118) and configured to engage the set of first claw teeth (110) to to prevent relative rotation between the first and second locking claws (92, 94),wherein the locking tongues (122) extend radially outward from the annular body (118) and are received in the locking openings (90), wherein the second locking claw (94) is movable along an axis (54) between a first position in which the set of second claw teeth (120) is disengaged from the set of first claw teeth (110) to permit relative rotation between the first side gear (80) and the differential case (60), and a second position in which the set of second claw teeth (120) engages the set of first claw teeth (110) to prevent relative rotation between the first side gear (80) and the differential case (60); wherein the locking openings (90) have a first locking surface (100) that is at least partially frustoconically shaped, and wherein the locking tongues (122) define a second locking surface (130) configured to mate with the first locking surface (100). [2] The limited-slip differential assembly (12) of claim 1, wherein the locking openings (90) extend completely through the first end wall (68). [3] Limited-slip differential assembly (12) according to claim 2, wherein a pressure plate (142) is overmolded over the locking tabs (122). [4] The limited-slip differential assembly (12) of claim 3, wherein the locking tabs (122) define a notch (164). [5] Limited-slip differential assembly (12) according to claim 1, wherein the set of second dog teeth (120) is formed without an undercut. [6] A method of forming a limited-slip differential assembly (12) comprising: Providing a first housing member (74) configured to be rotatable about a rotation axis (54), the first housing member (74) having a plurality of locking openings (90), each of the locking openings (90) defining a first locking surface (100) having a frustoconical shape; Installing a locking claw (94) on the first housing member (74), the locking claw (94) having a body (118), a set of second claw teeth (120) and a plurality of locking tongues (122), the set of second claw teeth (120) extending axially from the body (118), wherein the locking tabs (122) extend radially from the body (118) and are received in the locking openings (90), wherein the locking tabs (122) define a second locking surface (130) and are received in the locking openings (90), wherein at least a portion of the second locking surface (130) is frustoconically shaped and configured to mate with the first locking surface (100); and Installing a differential gear (62) in the first housing member (74), the differential gear (62) having a side gear (80) with a set of first dog teeth (110) configured to selectively mesh with the set of second dog teeth (120). [7] The method of claim 6, wherein the set of first claw teeth (120) is formed by fine blanking. [8] The method of claim 7, wherein the second locking surface (130) is formed by milling or embossing. [9] The method of claim 6, wherein each of the first locking surfaces (100) is formed by a rotating cutting tool (102) as the rotating cutting tool (102) is inserted into the first housing member (74) along an axis parallel to the rotational axis (54). [10] Axle assembly (10, 24) comprising: an axle housing (30); a limited-slip differential assembly (12) housed in the axle housing (30) and rotatable about a rotational axis (54), the limited-slip differential assembly (12) having a differential case (60), a differential gear (62), and a locking mechanism (64), the differential case (60) defining a cavity (66) and having a first end wall (68), the differential gear (62) being received in the cavity (66) and having a first side gear (80), the locking mechanism (64) comprising a plurality of locking openings (90), a first locking claw (92), and a second locking claw (94), the locking openings (90) being formed in the first end wall (68), the first locking claw (92) comprising a set of first claw teeth (110) fixedly coupled to the first side gear (80), the second Locking claw (94) has an annular body (118), a set of second claw teeth (120) and a plurality of locking tongues (122),wherein the set of second dog teeth (120) extends from the annular body (118) and is configured to engage the set of first dog teeth (110) to prevent relative rotation between the first and second locking dogs (92, 94), wherein the locking tongues (122) extend radially outwardly from the annular body (118) and are received in the locking openings (90) such that the second locking dog (94) is non-rotatably but slidably mounted on the differential case (60), wherein the second locking dog (94) is movable along the rotation axis (54) between a first position in which the set of second dog teeth (120) is disengaged from the set of first dog teeth (110) to permit relative rotation between the first side gear (80) and the differential case (60), and a second position in which the set of second Claw teeth (120) engage with the set of first claw teeth (110),to prevent relative rotation between the first side gear (80) and the differential housing (60), and, a pair of axle shafts (36) driven by the differential assembly (12); wherein the locking openings (90) have a first locking surface (100) that is at least partially frustoconical in shape, and wherein the locking tongues (122) define a second locking surface (130) that is at least partially frustoconical in shape to engage the first locking surface (100) respectively. [11] The limited-slip differential assembly (12) of claim 10, wherein the locking openings (90) extend completely through the first end wall (68). [12] Limited-slip differential assembly (12) according to claim 11, wherein a pressure plate (142) is overmolded over the locking tabs (122). [13] The limited-slip differential assembly (12) of claim 12, wherein the locking tabs (122) define a notch (164). [14] Limited-slip differential assembly (12) according to claim 10, wherein the set of second dog teeth (120) is formed without an undercut.

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