Patent Grant
9453569
1. Field
The present teachings relate generally to locking differentials for vehicles and, more specifically, to features of a locking differential having preload spring wear pads.
2. Description of the Related Art
Locking differentials of the type contemplated by the present teachings 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 an event requiring differential rotation between the axle half shafts, such as cornering, the higher speed axle shaft advances its clutch to an over-running condition, decoupling it from the powertrain torque. If the driving terrain provides insufficient traction to activate the over-running feature of the locking differential, or while driving in a straight line, torque is applied equally to both axle shafts.
While locking differentials of this type have generally worked for their intended purposes, certain disadvantages remain. More specifically, internally pre-loaded locking differentials typically use compression springs to provide the necessary slip resistance on the clutch packs to energize a ramping effect of the clutch members to cross pin interface. Given the required relative motion between the clutch members, the compression spring is “worked” between the two components. This motion causes “sliding” wear to both the compression spring and the clutch members. The interaction can also cause binding of the coils of the compression spring to the edges of the corresponding cavity or pocket. These conditions result in unintended forces acting within the interface that can increase the propensity of the differential being damaged.
Thus, there remains a need in the art for a locking differential that is designed so as to achieve control of the interaction of the clutch members and compression springs, thereby providing for smoother operation and reduced spring binding and breakage.
One aspect of the present disclosure relates to structures for reducing wear of pre-load springs in a differential.
Another aspect of the present disclosure relates to a differential that uses end cap structures (i.e., wear pads) to allow springs of the differential to apply pre-load forces between components of the differential while being completely enclosed/retained in a cavity (e.g., opening, hole, passage, etc.) defined by only one of the components.
A further aspect of the present disclosure relates to a locking differential for a vehicle including a rotatable 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 each corresponding pair of clutch members and the side gears. The clutch members are axially moveable within the housing to engage a respective one of the clutch mechanisms 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 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 each groove and operatively connected for rotation with the housing. At least one biasing member is disposed between the clutch members and at least one wear pad is disposed at the end of the at least one biasing member to preload the at least one biasing member and to allow the at least one biasing member to be acted upon by only a single clutch member.
In one aspect of the present teachings, by placing substantially cylindrical “wear pads” at the end of the compression springs, the compression springs are allowed to be acted upon by only a single clutch member. The “wear pad” is piloted within a bore of the compression spring, which provides a “length over distance” advantage to prevent “shear” or “wedging” effects. This also allows for an intentional and engineered contact at the sliding interface between the clutch member and the cross pin.
Other aspects of the present teachings will be readily appreciated, as the same becomes better understood after reading the subsequent description taken in connection with the accompanying drawings wherein:
One representative example of a locking differential of the type contemplated by the present teachings is generally indicated at 10 in
The differential 10 is enclosed within an axle housing 21 that protects the differential 10 and contains lubricant (e.g., oil) for lubricating moving parts within the axle housing 21. The differential housing 12 is mounted to rotate relative to the axle housing 21 about an axis of rotation A. In one example, bearings can be provided between the differential housing 12 and the axle housing 21 to allow the differential housing 12 to freely rotate about the axis of rotation A relative to the axle housing 21. The left and right axle shafts 30, 32 are co-axially aligned along the axis of rotation A.
In certain examples, the axle assembly can be incorporated into a vehicle, such as an all-terrain vehicle, a light utility vehicle, or other type of vehicle. The differential 10 of the axle assembly is configured to prevent or inhibit individual wheel spin and to provide enhanced traction performance on a variety of surfaces such as mud, wet pavement, loose dirt and ice. In use, torque for rotating the differential housing 12 about the axis of rotation A is provided by the drive gear 16 that intermeshes with the ring gear 14 carried by the differential housing 12. The differential mechanism 38 includes left and right clutches (e.g., disc-style clutches) configured to transfer torque from the rotating differential housing 12 to the left and right axle shafts 30, 32 thereby driving rotation of the left and right wheels 17, 19.
When the vehicle is driven straight, the left and right clutches are both actuated such that torque from the differential housing 12 is transferred equally to the left and right axle shafts 30, 32. When the vehicle turns right, the left clutch is de-actuated while the right clutch remains actuated. In this state, the differential mechanism 38 continues to drive rotation of the right axle shaft 32 while the left axle shaft 30 is allowed to free wheel at a higher rate of rotation than the right axle shaft 32. When the vehicle makes a left turn, the right clutch is de-actuated while the left clutch remains actuated. In this state, the differential mechanism 38 continues to drive rotation of the left axle shaft 30 while the right axle shaft 32 is allowed to free wheel at a higher rotational speed than the left axle shaft 30.
The ring gear 14, pinion gear 16, and drive shaft 18 are shown in phantom in
The first body 20 defines a hub 28 that supports one 32 of the pair of axle shafts 30, 32. Similarly, the second body 22 defines an opposed hub 34 that supports the other one 30 of the pair of axle shafts 30, 32. Together, the first body 20 and second body 22 of the housing 12 cooperate to define a cavity 36. As illustrated in
The differential mechanism 38 includes a pair of clutch members (e.g., left and right clutch members 40) disposed in spaced axial relationship with respect to one another. The clutch members 40 are operatively supported for rotation with the housing 12 and are co-axially aligned along the axis A. Left and right side gears 42, 44 (i.e., side hubs) are each operatively adapted for rotation with a corresponding one of the left and right axle shafts 30, 32. The side gears 42, 44 and axle shafts 30, 32 are co-axially aligned along the axis A. The side gears 42, 44 each define a plurality of splines 46 on the inner circumference thereof that are matingly received in corresponding splines defined on their corresponding axle shafts 30, 32. Left and right clutch mechanisms 48, 50 are operatively disposed between the clutch members 40 and their corresponding side gears 42, 44. When actuated, the clutch mechanisms 48, 50 are configured to transfer torque from the clutch members 40 to their respective side gears 42, 44 so as to resist or prevent relative rotation about the axis A between the clutch members 40 and their respective side gears 42, 44.
The side gears 42, 44 include a plurality of splines 52 on the outer circumferences thereof. The clutch mechanisms 48, 50 include a plurality of friction disks 54 that are cooperatively splined to the outer circumferences of the side gears 42, 44 and are rotatable therewith. Similarly, each of the clutch members 40 includes a plurality of splines 56 formed on the inner circumference thereof. A series of plates 58 have outer splines that engage the splined inner circumference 56 of the left and right clutch members 40. The plates 58 are interleaved between the friction disks 54 supported on the side gears 42, 44. The plates 58 and the friction discs 54 form clutch packs 59 (
The clutch members 40 are axially moveable along the axis A within the housing 12 to engage/actuate their respective clutch mechanism 48, 50 by axially compressing together the plates 58 and friction discs 54 (i.e., the clutch packs 59). When the clutch mechanisms 48, 50 are actuated, torque is transferred from the clutch members 40, through the clutch packs 59, to the side gears 42, 44 and their corresponding axle shafts 30, 32. When both clutch mechanisms 48, 50 are fully actuated, the housing 12, the clutch members 40, the side gears 42, 44, and the axle shafts 30, 32 all rotate in unison with each other about the axis A. One representative example of the locking differential 10 of the type contemplated by the present teachings may also employ a plurality of biasing members (described below) to pre-load the clutch packs. Also, thrust washers may be provided at inboard and outboard sides of the clutch packs.
Referring to
The grooves 64 are defined at the inwardly directed faces 62 of the clutch members 40. Each groove 64 is defined by ramp surfaces 65 that converge toward a neutral position 67. The neutral positions 67 form the deepest portions of the grooves 64. The clutch members 40 can rotate a limited amount relative to the cross pin 66 about the axis A between actuated positions where the cross pin 66 engages (e.g., rides on) the ramp surfaces 65 and non-actuated positions where the cross pin 66 is offset from the ramp surfaces 65 and aligns with the neutral positions 67. Each groove 64 includes two groove portions 64a, 64b (see
When the cross pin 66 is aligned with the neutral positions 67 of the grooves 64 of one of the clutch members 40, the corresponding clutch pack 59 is not axially compressed by the corresponding clutch member 40 and is therefore not actuated. When the clutch pack 59 is not actuated by its corresponding clutch member 40, only pre-load is applied to the clutch pack. In this non-actuated state, the clutch plates and the friction discs can rotate relative to one another during a wheel overspeed condition. Thus, during a wheel overspeed condition, the non-actuated clutch pack 59 corresponding to the overspeeding wheel permits the corresponding side gear 42, 44 and its corresponding axle shaft 30, 32 to rotate relative to the corresponding clutch member 40.
During normal straight driving conditions, the cross pin 66 engages the ramp surfaces 65 causing actuation of the clutch mechanisms 48, 50 such that the clutch packs 59 prevent relative rotation between the clutch members 40 and their corresponding side gears 42, 44. Thus, driving torque is transferred from the differential housing 12 and cross pin 66 through the clutch members 40, the clutch packs, and the side gears 42, 44 to the axle shafts 30, 32 and the wheels 17, 19. Thus, with both clutch packs 59 actuated, the differential housing 12, cross pin 66, the clutch members 40, the side gears 42, 44, the axle shafts 30, 32, and the wheels 17, 19 all rotate in unison about the axis A. During an overspeed condition (e.g., during a turn), the clutch member 40 corresponding to the overspeeding wheel rotates relative to the cross pin 66 such that the cross pin 66 disengages from the ramp surfaces 65 and becomes aligned with the neutral positions 67 thereby causing the corresponding clutch pack 59 to no longer be actuated. With the clutch pack 59 no longer actuated, only pre-load pressure is applied to the corresponding clutch pack. The pre-load pressure is sufficiently low that the de-actuated clutch permits relative rotation between the clutch member 40 and its corresponding side gear 42, 44 to accommodate the faster rotation of the overspeeding wheel relative to its corresponding clutch member 40, the cross pin 66 and the differential housing 12.
An intermating stop arrangement 100 defined between the inboard sides of the clutch members 40 allows for only a limited range of relative rotational movement between the clutch members 40 about the axis A. The stop arrangement 100 ensures that the clutch members 40 don't over-rotate their corresponding neutral positions 67 past the cross pin 66 during an overspeed condition. If the clutch members 40 were to over-rotate during an overspeed condition, the cross pin 66 would inadvertently actuate a de-actuated clutch by engaging the ramp 65F, 65R on the opposite side of the neutral position 67. The stop arrangement 100 prevents this from happening thereby allowing the overspeeding wheel to maintain an overspeed condition during a turn without interference from the clutch mechanisms 42, 44. The clutch pre-load is sufficiently high to provide the necessary slip resistance on the clutch packs 59 to energize the ramping effect of the clutch members to cross pin interface during clutch actuation.
In one representative example of the locking differential 10 of the type contemplated by the present teachings, the locking differential 10 includes a plurality of biasing members 70 (e.g., springs) that are disposed between the clutch members 40 and received in pockets or cavities 72 formed in the opposed clutch members 40 at the inboard sides of the clutch members 40 to urge the clutch members 40 away from one another. The biasing members 70 are depicted as compression springs having a plurality of coils 73. The biasing members 70 are made of a metallic material. The locking differential 10 also includes a plurality of wear pads 74 that are disposed in the cavities 72 between the end of the biasing members 70 and the clutch members 40 to preload the biasing members 70.
The wear pads 74 are generally or substantially cylindrical in shape. The wear pads 74 are made of a metallic material. The wear pads 74 have an enlarged head 76 which may include a recess 77. The wear pads 74 also have a shaft 78 extending axially from the head 76. Each wear pad 74 is disposed in a corresponding cavity 72 such that the shaft 78 extends into a bore 80 of the biasing member 70 and the head 76 abuts one of the coils 73 of the biasing member 70 and the opposed clutch member 40. It should be appreciated that, by placing the wear pads 74 at the end of the biasing members 70, the biasing members 70 are allowed to be acted upon by only a single clutch member 40. It should also be appreciated that the wear pad 74 is piloted within the bore 80 of the biasing member 70, which provides a “length over distance” advantage to prevent “shear” or “wedging” effects and allows for an intentional contact at the sliding interface between the clutch member 40 and the cross pin 66.
The wear pads 74 allow the biasing members 70 to apply a biasing load while remaining fully enclosed/contained within their corresponding cavities 72. The biasing forces from the biasing members 70 are transferred axially through the wear pads 74. The wear pads 74 traverse an interface gap between the clutch members 40. In this way, the biasing members 70 do not traverse the interface gap between the clutch members 40. Thus, the biasing members 70 are not exposed to side loads generated when the clutch members 40 rotate relative to one another about the axis A when one of the clutch members 40 encounters an overspeed condition. Instead, such side loading is applied to the wear pads 74.
The biasing members 70 function to provide pre-load that pre-compresses the clutch packs 59 to provide the necessary slip resistance to ensure proper actuation of the clutch packs 59. The pre-load provided by the biasing members 70 should be large enough such that the clutch packs 59 provide sufficient resistance to rotational movement of the clutch members 40 about the axis A for the cross pin 66 to ride up on the ramps 65 and cause actuation of the clutch mechanisms as differential housing 12 and the cross pin 66 carried therewith are rotated about the axis A during normal driving conditions. Also, the pre-load provided by the members 70 should not be so large so as to cause the wheels to slip/skid relative to the ground/road surface when encountering an overspeed wheel condition. In one example, the clutch pre-load applied to each clutch pack 59 allows the clutch packs 59 to transfer a pre-load torque value that is less than a representative wheel slip torque value corresponding to the outside wheel during a turn. The representative wheel slip torque value (i.e., the torque required to have the wheel slip relative to the ground) is dependent upon the gross weight of the vehicle and a selected coefficient of friction between the ground and the wheel that corresponds to a low traction condition.
As illustrated in
The biasing members 70 in the example of
The present teachings have been described in great detail in the foregoing specification, and it is believed that various alterations and modifications of the many aspects of the present teachings will become apparent to those ordinary skilled in the art from a reading and understanding of the specification. It is intended that all such alterations and modifications are included in the present teachings, insofar as they come within the scope of the appended claims.
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This application is a Continuation of PCT/US2013/072185, filed on 27 Nov. 2013, which claims benefit of U.S. Patent Application Ser. No. 61/730,560 filed on 28 Nov. 2012, and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications.
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| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2013/072185 | Nov 2013 | US |
| Child | 14575537 | US |
