Patent Publication Number: US-6702708-B2

Title: Two-way roller clutch assembly

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application from U.S. patent application Ser. No. 09/908,402, filed Jul. 18, 2001 now U.S. Pat. No. 6,595,337 which claims the benefit of related provisional application Ser. No. 60/223,882 filed Aug. 8, 2000. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention is related to a vehicle drive line having differential equipped with a two way over-running clutch. More specifically, the present invention relates to a vehicle drive line having a differential equipped with a two-way over-running clutch assembly of a roller/ramp variety which can be controlled for selectively locking up an automotive differential assembly. 
     BACKGROUND OF THE INVENTION 
     This invention is related to devices and methods as described in U.S. Provisional Application No.: 60/223,882, filed Aug. 8, 2000, and U.S. Provisional Application No.: 60/258,383, filed Dec. 27, 2000, all of which are commonly assigned. 
     Differential assemblies are used in motor vehicles to allow the wheels to turn at different rotational speeds while still providing power to the wheels. Various types of differential assemblies are used in motor vehicles to redirect the transfer of power to the driving axles. 
     In a standard differential, as a vehicle turns, power continues to be provided through pinion and ring gears to the differential housing. As the inner and outer wheels describe different circles or radii, side gears attached to axle shafts are allowed to turn at different speeds by the motion of intermediate spider gears. As long traction is maintained between the drive wheels and the road service, the power is properly distributed to the wheels through the differential assembly. However, when traction is reduced or lost altogether, a standard differential assembly will spin uselessly, providing little tractive power to the wheels. For instance, if one tire is on ice or some other slippery service while the other is on dry pavement, slip will occur at the low friction side and all the power through the differential assembly will be sent to the slipping tire. No power will be delivered to the wheel on the dry pavement and the vehicle will not be powered forward or backward. Therefore, there is a need to lock the axle halves together in certain situations. 
     A differential assembly design that is used to overcome the shortcomings of the standard differential assembly is known as the locking differential. A locking differential typically engages a “dog” clutch or an axial gear set to lock the two axle halves together. Unfortunately, locking differentials cannot be engaged “on-the-fly” because any relative motion between the gear teeth would result in severe mechanical damage. It would be desirable to selectively lock the differential assembly instantaneously during “on-the-fly” operation. 
     It is known in the art to selectively lock other drivetrain components using roller/ramp clutch assemblies. For example, the two-way over-running clutch assembly described in U.S. Pat. No. 5,927,456, assigned to NTN Corporation, and hereby incorporated by reference, describes a clutch assembly of a roller ramp variety and the mechanism by which the rollers are retained and biased in the assembly. In addition, the rotation transmission device described in U.S. Pat. No. 5,924,510, also assigned to NTN Corporation, and hereby incorporated by reference, discloses a device which includes a clutch assembly mounted in the transfer case of a four-wheel drive vehicle that can selectively transmit a driving force. 
     It would be desirable to provide this technology for use with differential assemblies to selectively lock the two axle halves together during “on-the-fly” operation. 
     A primary object of this invention is therefore to provide a two-way over-running clutch mechanism, such as that disclosed in U.S. Pat. Nos. 5,927,456 or 5,924,510, installed in the differential assembly of a motor vehicle which when energized will lock together a side gear or drive axle and the differential housing so that no relative rotation can occur between the two drive wheels. This system will provide on-demand traction and can be controlled by an electromagnetic trigger clutch or by hydraulic, pneumatic or other means. 
     Another object of the present invention is to provide a differential assembly which can be selectively locked together instantaneously during “on-the-fly” operation. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with an aspect of the present invention an over-running clutch assembly comprises an outer race having a cylindrical inner surface and being rotatable about an axis and a case end enclosing a first end of the outer race, an inner race having a segmented (flat or slightly concave) outer surface coaxial with the cylindrical inner surface and defining a gap therebetween. The inner race is rotatable about the axis with rotational movement relative to the outer race. A plurality of ramp surfaces formed at spaced apart locations on the outer surface define a plurality of cammed surfaces on the outer surface of the inner race. A plurality of rollers are positioned between the outer race and the inner race with one of the rollers being located centrally within each of the cammed surfaces and each of the rollers having a diameter less than the gap between the center of the cammed surface on the inner race and the cylindrical inner surface of the outer race. A retainer interconnects all of the rollers and causes the rollers to circumferentially move in unison with one another. The retainer is rotatable about the axis with limited relative rotation with respect to the inner race. A first biasing element is supported on the retainer to radially bias the retainer position relative to the inner race such that each of the rollers is held in the center of the flat cammed surfaces on the inner race. An actuation disk is connected to the retainer by a means which allows some axial movement of the activation disk with respect to the retainer toward the case end. The preferred method would include a retainer tab extending axially from one end of the retainer and a notch which is adapted to engage the retainer tab thereby preventing circumferential or relative rotational motion of the actuation disk relative to the retainer and allowing axial motion of the actuation disk relative to the retainer. A second biasing element is disposed between the actuation disk and the inner axial surface of the case end to bias the actuation disk away from the case end. 
     The clutch assembly includes an actuator to selectively overcome the second biasing element to force the actuation disk into contact with the case end, wherein rotation of the outer race and case end with respect to said inner race is frictionally transferred to the actuation disk and the retainer, overcoming the first biasing element, thereby moving the rollers along the ramp surfaces to a position where the rollers engage and wedge between the inner and outer races to prevent relative rotation between the inner and outer races. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial sectional view of a portion of a vehicle driveline of the present invention; 
     FIG. 2 is a perspective view of an over-running clutch of the present invention; 
     FIG. 3 is a side sectional view of the over-running clutch of FIG. 2; 
     FIG. 4 is a detail of a portion of the over-running clutch of FIG. 3; 
     FIG. 5 is perspective view of the assembly of the inner race, the retainer, the rollers and the actuation disk for the over-running clutch; 
     FIG. 6 is a sectional view of FIG. 5 taken along line  6 — 6 ; 
     FIG. 7 is a perspective view of a differential housing with an over-running clutch of the present invention; and 
     FIG. 8 is side sectional view of the differential housing of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description of the preferred embodiment of the invention is not intended to limit the scope of the invention to this preferred embodiment, but rather to enable any person skilled in the art to make and use the invention. 
     Referring to FIG. 1, a driveline assembly of the present invention is generally shown at  2 . The driveline assembly  2  includes first and second axle half-shafts  4  (one shown) supported within an axle housing  6 . A rear differential  100  having a differential housing  102  is rotatably mounted within the axle housing  6 . An over-running clutch assembly  10  is coupled to the differential housing  102  and one of the axle half-shafts  4 . 
     Referring to FIGS. 2-4, the over-running clutch assembly  10  of the present invention includes an outer race  12  having a cylindrical inner surface  14  and is rotatable about an axis  16 . The outer race  12  includes a case end  18  enclosing a first end of the outer race  12 . The clutch assembly  10  also includes an inner race  20  having a cammed outer surface  22  coaxial with the cylindrical inner surface  14  of the outer race  12 . The inner surface  14  of the outer race  12  and the outer surface  22  of the inner race  20  define a gap  24  between the inner race  20  and the outer race  12 . The inner race  20  is rotatable about the axis  16 . The outer race  12  includes a flange  26  or other means for mounting the clutch assembly  10  to a differential housing  28 . Preferably, the rollers  34 , the inner race  20  and the outer race  12  are made from steel. Due to the high hertzian contact stresses experienced by the rollers  34 , the inner surface  14  of the outer race  12  and the outer surface  22  of the inner race  20 , the inner surface  14  and outer surface  22  are preferably hardened and ground. 
     The outer surface  22  of the inner race  20  includes a plurality of ramp surfaces formed at spaced apart locations which define a plurality of cammed surfaces on the outer surface  22  of the inner race  20 . A plurality of rolling elements  34  are positioned between the outer race  12  and the inner race  20  with one roller  34  being located at the center of each of the cammed surfaces of the inner race. The rolling elements  34  have a diameter which is smaller than the gap  24  between the inner surface  14  and the midpoint of the cammed outer surface  22 , but greater than the gap between the outer portions of the cammed surfaces and the inner surface  14 . A retainer  36  interconnects all of the rolling elements  34  and causes the rolling elements  34  to circumferentially move in unison with one another. The retainer  36  is rotatable about the axis  16  with limited relative rotation with respect to the inner race  20 . The retainer  36  also includes a retainer tab  38  extending axially toward an inner surface  40  of the case end  18 . A distal end  42  of the retainer tab  38  is adjacent the inner surface  40  of the case end  18 . 
     A first biasing element  81  is mounted onto the retainer  36  to maintain the position of the retainer with respect to the inner race such that the rollers are normally held in the middle of the cammed surfaces. An actuation disk  46  is disposed between the retainer  36  and the inner surface  40  of the case end  18 . The actuation disk  46  has an outer diameter  48  and an inner diameter  50 . The actuation disk  46  further includes a notch  54  located radially about the outer diameter  48 . The notch  54  is adapted to engage the retainer tab  38  thereby preventing rotational motion of the actuation disk  46  relative to the retainer  36 , while allowing axial motion of the actuation disk  46  relative to the retainer  36 . A second biasing element  56  is disposed between the actuation disk  46  and the inner surface  40  of the case end  18  to bias the actuation disk  46  away from the case end  18  and toward the retainer  36 . Preferably, the second biasing element  56  is a wave spring. 
     In the preferred embodiment, the first biasing element is a centering spring supported by the retainer  36  and engaging the inner race  20  to keep the retainer in position to keep the rolling elements  34  in the center of the cammed surfaces of the inner race  20  to allow the outer race  12  and the inner race  20  to rotate freely with respect to each other. The centering spring includes a plurality of small tangs (not shown) extending radially in or out to engage small notches (not shown) on the hub  72  of the inner race  20 . The biasing force of the centering spring must be carefully calibrated for the clutch assembly  10 . The centering spring must provide enough force to move the retainer  36  and rolling elements  34  to the neutral position easily when the clutch assembly  10  is dis-engaged, but not so much force that the friction between the actuation disk  46  and the case end  18  cannot overcome it to actuate the clutch assembly  10 . 
     Referring to FIG. 5, the actuation disk  46  may further include grooves milled into one face to assist the displacement of lubricant, especially at low temperatures when the viscosity can increase to such levels that actuation is impaired. These grooves can be radial or circumferential, or even spiral in both directions to assist the “corkscrewing” of the thickened lubricant out of the interface zone as the parts rotate relative to each other. 
     The clutch assembly  10  includes an actuator  58  to selectively overcome the second biasing element  56  to force the actuation disk  46  into contact with the case end  18 . The actuation disk  46  is free to move axially with respect to the retainer  36 , so when the attractive force of the actuator  58  overcomes the force of the second biasing element  56 , the actuation disk  46  will move axially toward the inner surface  40  of the case end  18  until the actuation disk  46  contacts the inner surface  40  of the case end  18 . When the actuation disk  46  is brought into contact with the inner surface  40  of the case end  18 , the relative rotational motion of the outer race  12  and case end  18  with respect to the actuation disk  46  will frictionally be transferred to the actuation disk  46 . The actuation disk  46  is linked rotationally and circumferentially to the retainer tabs  38 , therefore the rotational movement of the outer race  12  and case end  18  will be transferred through the actuation disk  46  and to the retainer  36 . 
     Rotational movement of the retainer  36  with respect to the inner race  20  moves the rolling elements  34  along the ramped surfaces until the rolling elements  34  are no longer in the centers of the cammed surfaces. Since the gap  24  is not large enough to accommodate the diameter of the rolling elements  34 , when the rolling elements  34  move out of the centers of the cammed surfaces, the rolling elements  34  become wedged between the outer surface  22  of the inner race  20  and the inner surface  14  of the outer race  12 , thereby locking the inner race  20  and outer race  12  together rotationally. The ramped surfaces are designed such that when the rolling elements  34  wedge between the inner and outer races  12 ,  20  an angle is formed between the ramped surfaces of the inner race  20  and a line tangent to the inner surface  14  of the outer race  12 . In order for the rolling elements  34  to wedge properly between the inner surface  14  of the outer race  12  and the outer surface  22  of the inner race  20 , the angle defined by the ramped surfaces and a line tangent to the inner surface  14  of the outer race  12  is preferably between approximately four degrees and approximately ten degrees. If this angle is too small, then the hertzian contact forces will be too high, crushing the rolling elements  34  and brinnelling the surfaces of the inner and outer races  12 ,  20 . If the angle is too large, the rolling elements  34  will squirt out from between the inner surface  14  of the outer race  12  and the outer surface  22  of the inner race  20 . The ramped surfaces and the interaction of the ramped surfaces with the rolling elements  34  are described in detail in U.S. Pat. Nos. 5,927,456 and 5,924,510 which are both assigned to NTN Corporation and are hereby incorporated by reference into this application. 
     In the preferred embodiment, the actuator  58  comprises an electromagnetic coil  60  held within a housing  62  mounted to an exterior surface of the stationary axle housing  6 . The case end  18  includes a plurality of partially circumferential slots  66  extending through the case end  18  and spaced radially about the case end  18 . When energized, the electromagnetic coil  60  produces a magnetic flux which is focused around the slots  66  and concentrated on the actuation disk  46 . When the magnetic flux passes through the actuation disk  46 , the actuation disk  46  is magnetically drawn toward the inner surface  40  of the case end  18 . Once the magnetic force of the electromagnetic coil  60  overcomes the force of the second biasing element  56 , the actuation disk  46  will start to move toward the inner surface  40  of the case end  18 . 
     Preferably, the actuator  58  is an electromagnetic coil  60 , however it is to be understood, that the present invention could be practiced with an actuator  58  of some other type. The actuation disk  46  could be moved through hydraulic or pneumatic means as well as through electromagnetic means. The present invention allows the actuator  58  to be mounted directly to the stationary axle housing in a drive line assembly, thereby allowing the differential to fit within existing axle carriers to make replacement cost efficient. 
     When the actuator  58  is de-energized, the magnetic attraction of the actuation disk  46  to the inner surface  40  of the case end  18  dissipates. As this attraction dissipates, the force of the second biasing element  56  quickly overcomes the dissipating magnetic attraction and forces the actuation disk  46  back away from the inner surface  40  of the case end  18 , thereby eliminating the frictional transfer of rotation to the actuation disk  46 . Without a rotational force to pull the retainer  36  and rollers  34  out of the neutral position, the first biasing element  81  will force the retainer  36  back into the neutral position and the rollers  34  back into the middle of the cammed surfaces, thereby allowing the outer race  12  to rotate freely with respect to the inner race  20 , and un-locking the clutch assembly  10 . 
     In the preferred embodiment, the actuation disk  46  includes an annular step  82  extending around the inner diameter  50  of the actuation disk  46 . The annular step  82  faces the inner surface  40  of the case end  18 , and provides a recess into which the second biasing element  56  is piloted and can collapse into when the actuation disk  46  is drawn to the inner surface  40  of the case end  18 . Preferably, the second biasing element  56  is a wave spring that fits within the annular step  82  on the actuation disk  46  and collapses within the annular step  82  when the force of the electromagnetic coil  60  exceeds the spring force of the wave spring  56 . 
     Preferably, the housing  62  for the electromagnetic coil  60  is mounted to the stationary axle carrier and is located with respect to the case end  18  by a bearing  68 . The bearing  68  can be a ball, roller or journal bearing and will allow the electromagnetic coil  60  and the housing  62  to remain stationary with respect to the axle housing/carrier. This will allow wiring to the electromagnetic coil  60  to be simplified because an electrical connection to a rotating body is not required. A journal bearing or some other type of bearing could also be used. Any means suitable to allow relative rotational movement between the housing  62  and the exterior surface of the case end  18  is adequate. 
     Referring to FIGS. 5 and 6, in the preferred embodiment, the inner diameter  50  of the actuation disk  46  includes a series of inner notches  70 . The inner race  20  includes a hub  72  adjacent the cammed outer surface  22  which includes a step  74  extending radially and axially outward. The step  74  extends axially toward the inner surface  40  of the case end  18  leaving a space  76  between the step  74  and the inner surface  40  of the case end  18 . The height of the actuation disk  46  is sized to fit within that space  76  such that the step  74  engages the inner notch  70  when the actuation disk  46  is biased toward the retainer  36 . This locks the actuation disk  46  rotationally to the hub  72  of the inner race  20 . This is helpful to insure that the actuation disk  46  will not inadvertently rotate and cause the clutch  10  to lock up by mistake. This can happen when the viscosity of the oil within the clutch  10  and the rotational speed of the outer race  12  combine to frictionally rotate the actuation disk  46  without the actuator  58  attracting the actuation disk  46  to the inner surface  40  of the case end  18 . As long as the inner notch  70  within the actuation disk  46  is engaged with the step  74  on the hub  72 , the actuation disk  46  cannot rotate, and the clutch  10  cannot be inadvertently locked up. 
     When the electromagnetic coil  60  is actuated and draws the actuation disk  46  toward the case end  18 , the notches  70  on the inner diameter of the actuation disk  46  will clear the step  74  just before coming into contact with the inner surface  40  of the case end  18 , thereby allowing the actuation disk  46  to rotate freely within the space  76  between the step  74  and the inner surface  40  of the case end  18  and allowing the clutch  10  to lock up. Preferably, the step  74  is formed on the hub  72  of the inner race  20 , however, it is to be understood that the step  74  could be formed on a ring  78  that is press fit onto the hub  72  of the inner race  20 . 
     In the preferred embodiment, the retainer tabs  38  extend directly from the retainer  36 , however, alternatively, the clutch assembly  10  could include an actuation spider  80  mounted to the retainer  36  as shown in FIGS. 4 and 5. The actuation spider  80  is rotationally locked to the retainer  36  such that the actuation spider  80  and the retainer  36  functionally act as one component. The first biasing element  81  acts against the retainer  36 , holding the retainer in position with respect to the inner race  20 . The retainer tabs  38  extend from the actuation spider  80  to engage the notches  54  within the outer diameter  48  of the actuation disk  46 . 
     Referring to FIGS. 1,  7  and  8 , the differential housing  102  includes an input ring gear  103  mounted to an outer diameter  104  of the housing  102 . Rotational motion from the drive train of the vehicle is transferred to the differential housing  102  through this ring gear. A first side gear  106  and a second side gear  108  are mounted within the differential housing  102  and are attached to first and second axle half-shafts  4  (one shown) of the vehicle. Two or more spider gears  110  are mounted in the differential housing  102  so that they match with the first and second side gears  106 ,  108 . 
     During normal straight line operation, the power provided is transmitted through the ring gear to the differential housing  102 . Because there is no relative rotational speed differences between the two axles during normal straight line operation, the differential housing  102  and axles rotate at the same speed, and there is no relative motion between the side gears  106 ,  108  and the spider gears  110 . When the vehicle turns, rotational speed differences between the two axles are caused by the differently sized circles being described by the tires on each side of the vehicle. As the axles turn at different speeds, side gears  106 ,  108  also turn at different speeds, but the spider gears  110  keep the two axles meshed together and torque is split proportionally between the two sides. 
     The clutch assembly  10  is mounted within the differential housing  102  to allow both the axles of the vehicle to be locked together by locking the first side gear  106  rotationally to the differential housing  102 . Referring to FIG. 8, the second side gear  108  is rotatably mounted within the differential housing  102  at a second end  114 . The second side gear  108  is fixed axially, but is allowed to rotate independently of the differential housing  102 . The outer race/case end of the roller clutch  10  is fixedly mounted to the differential housing  102  at a first end  112 . 
     As shown in the figures, the clutch assembly  10  and the differential housing  102  can each include a flange  116 ,  118  to allow them to be attached to one another with mechanical fasteners. However, it is to be understood, that an outer diameter  120  of the outer race  12  of the clutch assembly  10  and an inner diameter  122  of the first end  112  of the differential housing  102  can be formed with splines therein and sized such that the clutch assembly  10  can be press fit within the inner diameter  122  of the first end  112  of the differential housing  102  to eliminate the need for mechanical fasteners. 
     The first side gear  106  is fixedly mounted to the inner race  20  of the clutch assembly  10 . In the preferred embodiment, the inner race  20  includes a center bore  124  and the first side gear  106  includes an outer diameter  126 , wherein the center bore  124  of the inner race  20  and the outer diameter  126  of the first side gear  106  are adapted to be press fit or splined together. The center bore  124  of the inner race  20  and the center bore of the first side gear  106  may also have splines formed on them to connect each to a common spline on the first axle/half shaft, to prevent any relative rotational movement between the inner race  20  and the first side gear  106 . In all of these embodiments, the first side gear  106  and the inner race  20  are locked together and functionally act as one component. 
     The spider gears  110  are mounted within the housing  102  and rotate about a first axis  128  defined by a shaft  129  mounted therein. The first and second side gears  106 ,  108  are mounted to the differential housing and rotate about a second axis  130  defined by the first and second axle half-shafts which is perpendicular to the first axis. The spider gears are mounted within the housing and on the shaft and are engaged with both the first and second side gears  106 ,  108 . 
     When the clutch assembly  10  is dis-engaged, the inner race  20  and the outer race  12  are free to rotate relative to each other so the first side gear  106  and the first axle half shaft  109  are free to rotate relative to the differential housing  102 . If the rotational speed of the axle half-shafts are different, such as when the vehicle turns, the side gears  106 ,  108  also turn at different speeds, but the spider gears  110  keep the two axles meshed together and torque is split appropriately between the two sides. In conditions of poor traction (wet roads, snow, ice), one wheel can slip and the differential  100  doesn&#39;t allow the other wheel to carry any torque. Under these conditions, a vehicle can have trouble getting up even a low grade hill. 
     When the clutch assembly  10  is engaged, the first axle half-shaft, the first side gear  106 , the inner race  20 , the outer race  12  and the differential housing  102  are all locked together so that no relative rotation is allowed. When the first side gear  106  is locked rotationally to the differential housing  102 , the spider gears  110 , which are meshed with the first side gear  106  are prevented from rotating around the first axis  128 , and the second side gear  108 , which is meshed with the spider gears  110 , is prevented from rotational movement relative to the differential housing  102 . To simplify, when the clutch assembly  10  is engaged, the two side gears  106 ,  108 , and consequently the two axle half-shafts are effectively locked together so that torque is transferred to both axle half-shafts equally and no relative rotation between the two axle half-shafts is allowed. 
     The foregoing discussion discloses and describes one preferred embodiment of the invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that changes and modifications can be made to the invention without departing from the true spirit and fair scope of the invention as defined in the following claims. The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.