Patent Publication Number: US-11655887-B2

Title: Clutch pack with lock plates

Description:
This is a US § 371 National Stage Entry of PCT/EP2020/050559 filed Jan. 10, 2020, and claims the benefit of Indian provisional application 201911001157 filed Jan. 10, 2019 all of which are incorporated herein by reference. 
     This application claims the benefit of priority of Indian Patent Application No. 201911001157, filed Jan. 10, 2019, which is incorporated herein by reference in its entirety. 
     FIELD 
     This application relates to clutch packs, and more particularly to clutch packs with lock plates for use in, for example, mechanical locking differentials. 
     BACKGROUND 
     A mechanical locking differential automatically locks a differential when a predetermined traction condition is encountered (e.g., a difference in wheel speed exceeding a predetermined valve). A mechanical locking differential typically uses an active clutch pack having a large number of clutch discs to provide the required torque capacity from the ring gear to the wheels and to smoothen the locking action. Such a large number of clutch discs may result in an extended bearing span. 
     In certain applications, it may be desirable to decrease the bearing span with smaller axial width. Reducing the number of clutch discs, however, may not be desirable because it can reduce the torque capacity and thereby prevent the smooth locking action. 
     SUMMARY 
     The apparatus and related methods disclosed herein may overcome one or more of the above-discussed disadvantages and improve the art by way of a combination of a clutch pack and a pair of lock plates. 
     To attain the advantages and in accordance with the purpose of the disclosure, as embodied and broadly described herein, one aspect of the disclosure may provide a differential comprising a case, a side gear, a first lock plate comprising a first side and a toothed side, and a second lock plate comprising a first side facing the case and a toothed second side facing the toothed side of the first lock plate. The differential can further comprise a cam plate between the side gear and the first lock plate and a clutch pack between the cam plate and the first lock plate. The cam plate can comprise a splined neck extending towards the first lock plate, and the clutch pack can comprise at least one active clutch disc internally splined to the splined neck. 
     Another exemplary aspect can provide a differential that comprises a case comprising a guide groove, a side gear comprising external splines, a first lock plate comprising internal splines configured to engage the external splines of the side gear, and a second lock plate configured to mate with the first lock plate. The differential can also comprise a cam plate comprising a neck extending from a side surface facing the first lock plate. The neck can comprise external splines. The differential can further comprise a clutch pack between the cam plate and the first lock plate, where the clutch pack can comprise at least one first clutch disc having an ear configured to fit into the guide groove of the case and a second clutch disc internally splined to the external splines of the neck. 
     According to still another exemplary aspect, a differential can comprise a case comprising a first end and a second end opposite to the first end, a first side gear comprising exterior splines, and a second side gear comprising exterior splines. The differential can also comprise a first lock plate comprising a first side and a toothed side, a second lock plate comprising a first side facing the second end of the case and a toothed second side facing the toothed side of the first lock plate, and a cam plate between the side gear and the first lock plate. The cam plate can comprise a splined neck extending towards the first lock plate. The differential can further comprise a first clutch pack between the cam plate and the first lock plate and a second clutch pack between the first side gear and the first end of the case. The first clutch pack can comprise at least one active clutch disc internally splined to the splined neck, and the second clutch pack can comprise at least one active clutch disc internally splined to the external splines of the first side gear. 
     Additional objects and advantages will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the disclosure. The objects and advantages will also be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the claimed invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an exemplary embodiment of the invention and together with the description, serve to explain the principles of the invention. 
         FIG.  1    is a perspective view of a mechanical differential. 
         FIG.  2    is a cross-sectional view of the mechanical differential of  FIG.  1   . 
         FIG.  3    is a perspective view of a lockup mechanism of the mechanical differential of  FIG.  2   . 
         FIG.  4 A  is a plan view of a first side of a cam plate. 
         FIG.  4 B  is a side view of the cam plate of  FIG.  4 A . 
         FIG.  4 C  is a plan view of a second side, opposite to the first side, of the cam plate of  FIG.  4 A . 
         FIG.  5    is a plan view of an inactive disc with friction surfaces. 
         FIG.  6    is a plan view of an internally splined active disc. 
         FIG.  7 A  is a plan view of a first side of a first lock plate. 
         FIG.  7 B  is a plan view of a second side, opposite to the first side, of the first lock plate of  FIG.  7 A . 
         FIG.  8 A  is a plan view of a first side of a second lock plate. 
         FIG.  8 B  is a plan view of a second side, opposite to the first side, of the second lock plate of  FIG.  8 A . 
         FIG.  9 A  is a cross-section view of a mechanical differential, illustrating an exemplary reaction block. 
         FIG.  9 B  is a plan view of  FIG.  9 A  along plane  9 C. 
         FIG.  9 C  is a perspective view of the reaction block of  FIG.  9 A . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the exemplary embodiments which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Directional references such as “left” and “right” are for ease of reference to the figures. 
     While the exemplary embodiment of the invention will be described in connection with a particular mechanical locking differential, it should be understood that the invention can be applied to, or used in connection with, any other types of locking differentials or any other suitable mechanical devices utilizing a clutch pack. 
       FIGS.  1  and  2    illustrate an example of a mechanical locking differential  1  configured to allow two wheels on a motor vehicle to operate at different speeds and maintain free differential action (i.e., unlocked mode). However, if one wheel begins to slip, the drive axle can be automatically and fully locked side to side, causing the wheels to rotate at the same speed and thereby providing full power to both wheels (i.e., locked mode). Such a mechanical locking differential uses a mechanical device, as opposed to an electrical or hydraulic device, to go between the locked mode and the unlocked mode. In various exemplary embodiments, the mechanical device consistent with the present disclosure can comprise one or more components described in U.S. Pat. Nos. 6,319,166, 7,438,661, 8,167,763, and 9,400,044, assigned to Eaton Corporation and incorporated herein by reference in their entireties. 
     Differential  1  can include a case  5  configured to house various components of differential  1 . Torque from a vehicle driveline can be transferred to differential  1  via an input gear (e.g., ring gear) (not shown). The input gear can be integrally formed with or attached to case  5  by suitable attachment mechanisms (e.g., bolts). The input gear can be in toothed engagement with an input pinion gear (not shown), which receives input drive torque from the vehicle driveline. 
     Differential  1  can further include a differential gear set disposed inside case  5 . In particular, differential  1  can include two side gears  100 ,  200  (i.e., hereinafter individually referred to as right side gear  100  and left side gear  200 ), a pinion shaft  60 , and one or more pinion gears  62 ,  68  rotatably mounted on pinion shaft  60 . Pinion shaft  60  can be attached to case  5  and connected to the input pinion gear. Pinion shaft  60  can be a cylindrical rod or, as shown in  FIGS.  9 A- 9 C , a cross-shaft  160  having a number of arms  175  corresponding to the number of pinion gears  162  mounted on pinion shaft  160 . It should be understood that any other suitable pinion shaft configuration known in the art can be used additionally or alternatively. 
     Side gears  100 ,  200  can be in splined engagement with a pair of axle shafts (not shown) of a motor vehicle. For example, each of side gears  100 ,  200  can have an internal spline  120 ,  220 , and the respective axle shaft can include a corresponding external spline (not shown), such that the torque of side gears  100 ,  200  can be transferred to the respective axle shafts. 
     Pinion gears  62 ,  68  can be meshed with side gears  100  and  200 , so that the power transferred from the engine to pinion shaft  60  can flow to the left and right axle shafts. For example, as pinion shaft  60  rotates, pinion gears  62  and  68  can transfer differentiated or undifferentiated torque to meshed side gears  100  and  200 . Torque can then be transferred to the respective axle shafts via the splined engagement therebetween and to the wheels associated with the axle shafts. Since this torque path, as well as rear wheel drive (RWD) and all-wheel drive (AWD or 4WD) torque paths, are known, the vehicle driveline is not illustrated. Despite the specific reference to FWD, RWD, and AWD systems, it is to be understood that differential  1  of the present disclosure can be used in any suitable environment requiring a differential rotation for two axle shafts. 
     During normal, straight-ahead operation of a motor vehicle, there may be limited differentiating action (e.g., substantially no differentiating action) that may occur between the left and right axle shafts, and pinion gears  62  and  68  may not rotate relative to pinion shaft  60 . Accordingly, case  5 , pinion gears  62  and  68 , side gears  100  and  200 , and the axle shafts all rotate about the same axis of rotation of the axle shafts, as a single solid unit. Under certain operating conditions, such as when the vehicle is turning, a certain amount of differentiating action may occur between side gears  100  and  200 , up to a predetermined level of speed difference (e.g., a difference of about 100 RPM between right side gear  100  and left side gear  200 ). Above that predetermined level, it can be desirable to retard the relative rotation between side gears  100  and  200  to prevent excessive differentiating action between the axle shafts. 
     To retard differentiating action between the axle shafts, differential  1  can include a lockup mechanism for locking up the differential gear set and an actuator for actuating the lockup mechanism. The lockup mechanism can include a combination of a clutch pack  40  and a pair of lock plates  1000 ,  2000  movably associated with a cam plate  300 . As shown in  FIGS.  4 A- 4 C , cam plate  300  can define a set of external teeth  310  extending from its radial outer surface. Cam plate  34  can also define a plurality of ramps  360  and a plurality of detents  370  (e.g., protrusions) on a cam surface facing left side gear  200 . Left side gear  200  can also define a cam surface (i.e., the backside of left side gear  200 ) with a plurality of corresponding ramps  260  and a plurality of corresponding detent-receiving holes (not shown) machined into the cam surface. Ramps  260  on left side gear  200  can mate between corresponding ramps  360  on cam plate  300 . The holes on the cam surface of left side gear  200  can prevent cam plate  300  from ramping until a predetermined torque is applied at external teeth  310  of cam plate  300 . 
     In some exemplary embodiments, detents  370  of cam plate  300  and the corresponding holes of left side gear  200  can be interchanged. For example, detents  370  can be formed on the cam surface of left side gear  200 , and the corresponding holes can be formed on the cam surface of cam plate  300 . 
     Cam plate  300  can also comprise a neck  330  extending from a side surface opposite to the cam surface. Neck  330  can include external splines (e.g., including teeth extending radially outwardly from an outer surface of neck  330 ), as best shown in  FIGS.  4 B and  4 C . One or both of ramps  360  of cam plate  300  and ramps  260  of left side gear  200  can comprise stepwise transitions or smooth transitions. Further, while four ramps  360 ,  260  are shown in  FIGS.  4 A and  4 B , more or fewer ramps can be used. Similarly, detents  370  of cam plate  300  and/or the corresponding holes of side gear  200  can have more or fewer than four shown in the figures. The configurations of cam plate  300  and side gear  200  and their relationship can be further understood from examples described in, for example, U.S. Pat. Nos. 3,606,803, 3,831,462, 5,484,347, 6,319,166, RE 28,004, 8,167,763 and 9,400,044, incorporated herein by reference in their entirety. 
     To actuate the lockup mechanism to lock differential  1 , any suitable actuator known in the art, such as those described in U.S. Pat. Nos. 8,167,763 and 9,400,044, can be used. For example, as shown in  FIG.  1   , actuator  500  can include a combination of an engagement mechanism  520  and a lockout mechanism  540 . Engagement mechanism  520  can comprise a pair of flyweights  525  spring-loaded on a first shaft that is meshed and rotates with external teeth  310  of cam plate  300 . When the first shaft rotates due to differential action and the rotational speed exceeds above a predetermined value (e.g., a difference of about 100 RPM), the centrifugal force of flyweights  525  overcomes the spring force and causes them to swing out to engage a pawl  545  of lockout mechanism  540  on a second shaft. One flyweight  525  can be configured to engage pawl  545  in one direction of rotation while the other flyweight  525  can be configured to engage pawl  545  in the opposite direction. The locking between flyweights  525  and pawl  545  can create a force exerted on external teeth  310  of cam plate  300  that causes cam plate  300  to rotate out of the detent position and into the ramping position, thereby initiating the locking mode. Because differential  1  may not lock at above a predetermined speed (e.g., 20 mph), lockout mechanism  540  can be configured to cause pawl  545  to rotate away from engagement mechanism  520  when the vehicle travels over the predetermined speed. Since actuator  500  of the present disclosure can be substantially similar to those described in the above-mentioned references, any additional details thereof is omitted herein. 
     Now with reference to  FIGS.  5 ,  6 ,  7 A -B, and  8 A-B, the lockup mechanism employing a combination of clutch pack  40  and a pair of lock plates  1000  and  2000  for use in, for example, a mechanical locking differential is described herein. As best shown in  FIG.  2   , the lockup mechanism of differential  1  can include a pair of first lock plate  1000  and second lock plate  2000  associated with left side gear  2000  and clutch pack  40  disposed between first lock plate  1000  and cam plate  300 . The lockup mechanism can also include another clutch pack  50  associated with right side gear  100 . 
     Clutch packs in a mechanical locking differential have two main functions: (1) to transfer whole torque from an input gear (e.g., ring gear) to the wheels of a motor vehicle when the differential is locked; and (2) to smoothen the locking action by slippage of the clutch itself. As will be evident from the description that follows, when lock plates  1000  and  2000  are used along with clutch packs  40  and  50  according to the present disclosure, the overall number of clutch discs required to maintain the torque capacity can be reduced, which in turn can reduce the bearing span. Accordingly, conventional clutch packs can be replaced with a combination of reduced-size clutch packs  40 ,  50  and locking plates  1000  and  2000  to reduce bearing span. 
     Referring to  FIGS.  7 A and  7 B , first lock plate  1000  can comprise internal splines  1050  (e.g., including teeth on an inner radial surface) configured to engage with the external splines of left side gear  200 . First lock plate  1000  can also comprise a plurality of face teeth  1020  extending axially from a periphery of a side surface facing second lock plate  2000 . 
     Referring to  FIGS.  8 A and  8 B , second lock plate  2000  can comprise a ring with a plurality of face teeth  2010  extending axially from a side surface facing first lock plate  1000 . Face teeth  2010  of second lock plate  2000  can be sized and configured to mate with face teeth  1020  of first lock plate  1000 . Second lock plate  2000  can also include a plurality of ears  2080  extending radially outwardly from its outer radial surface. Ears  2080  can fit into the guide grooves  3  formed in case  5  together with ears  12  of inactive clutch discs  10 ,  30  (see  FIG.  5   ), so that second lock plate  2000  can be locked from rotating with respect to inactive clutch discs  10 ,  30  and case  5 . The space between first lock plate  1000  and second lock plate  2000  can be sized such that ramps  360  of cam plate  300  can rest in valleys between ramps  260  of left side gear  200  in an unlocked mode (e.g., open mode). The spacing can be selected such that ramps  360  of camp plate  300  do not pass ramps  260  of left side gear  200  when cam plate  300  is locked. This design can enable positive locking such that differential  1  can operate either in a fully locked or unlocked mode. 
     Lock plates  1000  and  2000  serve as a positive locking element, whose torque carrying capacity is high with a lower axial width. If lock plates  1000  and  2000  are used alone, however, differential  1  may experience impact loading and the motor vehicle may experience locking jerk. To prevent such locking jerk and enable smooth locking action, the lockup mechanism can employ a synchronization mechanism comprising clutch packs  40 ,  50  and a disk spring  400 . As an active clutch disc exponentially increases the axial force acting on a clutch pack, an active clutch disc  80 ,  20  can be used in clutch pack  50  and clutch pack  40  for right side gear  100  and left side gear  200 , respectively, and each of clutch packs  40  and  50  uses a pair of externally ear-splined clutch discs  10 ,  30  and  70 ,  90 , respectively, as an inactive clutch discs. 
     As shown in  FIG.  5   , each inactive clutch disc  10 ,  30 ,  70 ,  90  can comprise a plurality of ears  12  extending radially outwardly from its outer radial surface. Ears  12  can fit into guide grooves  7  formed in case  5  with optional guide clips (not shown), so that inactive clutch discs  10 ,  30 ,  70 ,  90  can rotate with case  5 . In some exemplary embodiments, guide grooves  3  for receiving ears  2080  of lock plate  2000  and guide grooves  7  for receiving ears  12  of inactive clutch discs  10 ,  30  can be contiguous with or without step transitions to accommodate differences in dimensions. Alternatively, guide grooves  3  and guide grooves  7  can be provided separately. 
     Active clutch disc  20  can comprise splines  25  (e.g., including teeth on the inner radial surface) configured to engage the external splines on neck  330  of cam plate  300 , so that active clutch disc  20  can rotate with cam plate  300 . Similarly, active clutch disc  80  can be internally splined to external splines of right side gear  100 , so that active clutch disc  80  can rotate with right side gear  100 . Accordingly, on the right side of differential  1 , inactive clutch disc  90  engages case  5  on a first side and engages active clutch disc  80  on a second side. Inactive clutch disc  70  engages right side gear  100  on a first side and engages active clutch disc  80  on a second side. On the left side of differential  1 , inactive clutch disc  30  engages cam plate  300  on a first side and engages active clutch disc  20  on a second side. Inactive clutch disc  10  engages active clutch disc  20  on a first side and engages the non-toothed side of first lock plate  1000  on a second side. During the locking of differential  1 , active clutch disc  20  moves along externa splines of neck  330  of cam plate  300  to contact inactive clutch discs  10  and  30 , and active clutch disc  80  can move along external splines of right side gear  100  to contact inactive clutch discs  70  and  90 . At least inactive discs  30  and  70  can move so that ears  12  can slide in the guide grooves  3  of case  5 . Both side gears  100 ,  200  are then engaged by clutch packs  50  and  40 , respectively. 
     According to one exemplary aspect, as shown in  FIGS.  9 A- 9 C , differential  2  can comprise a reaction block  600  configured to transfer force between right side gear  100  and left side gear  200 . The reaction block  600  can also be included in differential  1  of  FIG.  2    to engage and disengage clutch packs  40  and  50 . In the disclosed exemplary embodiment, differential  2  can use a cross-shaft  160  having three uniformly-spaced arms  175  radially extended from a hub  170 . Hub  170  can be an annular ring defining a center hole  165  configured to receive reaction block  600 , as best shown in  FIG.  9 B . Reaction block  600  can be a two-piece construction of an identical thrust disc  610 . For example, as shown in  FIG.  9 C , thrust disc  610  can have a shape of a curbed disc with its center portion protruded outwardly to form a narrower neck portion  620 . Neck portion  620  can be sized and configured to be seated inside center hole  165  of cross-shaft  160  and can define a through-hole  650  in its center. As best shown in  FIG.  9 A , two thrust discs  610  can be arranged between right side gear  100  and left side gear  200  with their neck portions  620  seated inside center hole  165  of cross-shaft  160  and abutted against each other and with their wider flange portions  690  abutting against respective side gears  100  and  2000 . 
     It should be understood that any other suitable reaction block known in the art, such as the reaction block described in U.S. Pat. No. 8,167,763, can be used alternatively to pass force between right side gear  100  and left side gear  200  in either differential  1  or differential  2 . For example, the reaction block can be configured to provide an axial link between right side gear  100  and left side gear  200 . In differential  1 , force from left side gear  200  can be transferred through the reaction block to right side gear  100 , which transfers the force to clutch pack  50 . Similarly, force from right side gear  100  can be transferred through the reaction block to left side gear  200 , which transfers the force to clutch pack  40 . Accordingly, the reaction block can enable limited slip action. 
     In some exemplary embodiments, a reaction block can be omitted from differential  2 . For example, dimensions of differential  2  can allow placing inactive clutch discs from clutch pack  50  on right side gear  100  to clutch pack  40  on left side gear  200 . This results in a combination of clutch pack  40  with clutch pack  50 . One of the inactive discs  30 ,  70  can be omitted, while keeping the total number of active clutch discs  20 ,  80  the same. In these cases, the combined clutch pack  40 + 50  is on one side of differential  2 , no right hand clutch pack is used, and a reaction block can be omitted. This provides a smaller and light weighted differential. 
     Because the non-toothed side of lock plate  2000  engages with inactive clutch disc  10 , an additional friction surface can be provided between cam plate  300  and lock plates  1000 ,  2000 . Likewise, an additional friction surface can be provided between cam plate  300  and inactive clutch disc  30 . In one exemplary embodiment, friction surfaces can be provided on one or both of the non-toothed side of lock plate  1000  and on cam plate  300  on the side facing inactive clutch disc  30 . The friction surface can comprise, for example, a knurled pattern on a metal surface. In an alternative embodiment, a friction surface can be provided by treating a surface or by applying a friction material. For example, as shown in  FIG.  5   , inactive clutch discs  10 ,  30 ,  70 ,  90  can be provided with a carbon friction material applied to a metal surface. Active clutch discs  20 ,  80  can also be untreated or provided with a friction surface depending on the application. Differential locking and transfer of whole torque via friction can be enhanced in a smooth manner in a small footprint. 
     The synchronization mechanism can further comprise disk spring  400 , such as, for example, a Belleville washer, disposed between lock plates  1000 ,  2000  and an internal wall of case  5 . As the engagement of lock plates  1000  and  2000  require them to move axially, a reaction force needs to be generated against the ramping of cam plate  300 . Disc spring  400  can deflect and generate a spring reaction force with small or limited deflection towards lock plates  1000  and  2000  against the ramping of cam plate  300 . 
     While various operational characteristics of clutch packs  40 ,  50  with lock plates  1000 ,  2000  are evident from the description above, certain exemplary operational characteristics will be briefly described herein. During normal, straight-ahead operation of a motor vehicle (e.g., with little or no differentiating action occurring), the cam surface of left side gear  200  and the cam surface of cam plate  300  remain in a neutral position (i.e., no ramping) with cam plate  300  rotating with side gear  200  at the same rotational speed. 
     Under certain operating condition (e.g., the difference in rotational speed between side gear  100  and side gear  200  exceeding above about 100 RPM), actuator  500  can apply torque to external teeth  310  of cam plate  300 . The application of torque to external teeth  310  exceeding a predetermined level retards the rotation of cam plate  300  relative to left side gear  200  and causes the ramping of the cam surface of cam plate  300  and the cam surface of left side gear  200 . 
     The ramping of cam plate  300  causes cam plate  300  to move axially away from left side gear  200  and towards clutch pack  40  and lock plates  1000  and  2000 . At the same, in response to the ramping of cam plate  300 , disc spring  400  deflects and creates very high axial reaction force against the force exerted by cam plate  300 . Due to the axial reaction force, the axial movement of cam plate  300  can apply pressure to clutch pack  40 . The pressure applied to clutch pack  40  causes engagement between active disc  20  and inactive discs  10  and  30  (e.g., “loaded” condition). Since active disc  20  is in spline engagement with the outer splines on neck  330  of cam plate  300 , clutch pack  40  in the loaded condition causes the speed difference between left side gear  200  and case  5  to reduce. 
     As disc spring  400  deflects by a certain amount, disc spring  400  can create enough axial force to reduce a speed difference between first lock plate  1000  and second lock plate  2000  to a level at which they can engage with each other, creating a complete locking of differential  1 . For example, the axial force causes first lock plate  1000  and second lock plate  2000  to move axially towards one another, so that face teeth  1020  of first lock plate  1000  mate and lock with face teeth  2010  of second lock plate  2000 . Since first lock plate  1000  is in spline engagement with the outer splines of side gear  200 , and second lock plate  2000  is locked with case  5  via ears  2080  fitted into the guide grooves  3  of case  5 , the locking between first lock plate  1000  and second lock plate  2000  effectively prevents relative rotation between case  5  and side gear  2000 , thus retarding differentiating action between side gears  100  and  200 . 
     For unlocking, when left side gear  200  experiences torque reversal because of the lash that clutch packs  40  and lock plate  1000  have with respect to left side gear  200 , side gear  200  rotates in an opposite direction than that of the locking direction. At the same time, cam plate  300  rotates with left side gear  200 . This will reduce the axial force provided by disc spring  400  and causes lock plates  1000  and  2000  to disengage from one another. 
     Other implementations will be apparent to those skilled in the art from consideration of the specification and practice of the examples disclosed herein.