Abstract:
An over-running clutch includes an outer race and an inner race defining a gap therebetween. A plurality of rolling elements are positioned between the inner and outer races. A retainer interconnects the rolling elements. A first biasing element biases the retainer to hold the rolling elements such that the inner and outer races are free to rotate relative to one another. An actuator selectively forces the rolling elements to a position where the rolling elements engage and wedge between the inner and outer races, thereby locking the clutch. A sensor is adapted to detect the engagement of the clutch and to send a corresponding signal.

Description:
TECHNICAL FIELD OF THE INVENTION 
   This invention is related to a two way over-running clutch. More specifically, the present invention relates to a two-way over-running clutch assembly of a roller/ramp variety, which includes a lock indication device that sends a signal to indicate if the over-running clutch is engaged. 
   BACKGROUND OF THE INVENTION 
   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 to redirect the transfer of power to the driving axles. 
   In a standard open differential, as a vehicle turns, power is provided through a pinion and ring gear to the differential housing. As the inner and outer wheels trace paths of different radii, side gears attached to right and left axle half shafts are allowed to turn at different speeds by their interconnection through intermediate spider gears, which rotate with the housing. 
   As long as traction is maintained between the drive wheels and the road surface, the power is properly distributed to the wheels through the differential assembly. However, when traction is reduced or lost altogether at one or both wheels, a standard open differential assembly will cause one wheel to spin uselessly, providing little tractive power to the wheels. For instance, if one tire is on ice or some other slippery surface and the other tire is on dry pavement, slip will occur at the low friction side and the torque applied to the non-slipping tire will be limited to the torque generated at the slipping tire. In such circumstances, very little 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 half shafts together in certain situations causing both wheels to spin at about the same speed, irrespective of differing coefficients of friction encountered by the drive wheels. 
   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, and which is 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 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 torque. 
   Typically, these types of over-running clutches must include complex sensors to determine when the clutch is engaged and to send a signal to the operator of the vehicle indicating engagement status. Therefore, there is a need for an over-running clutch of the type described above that includes a simple, reliable lock indication device that will send a signal to the operator of the vehicle, or to the electronic control unit, indicating that the clutch is either engaged or disengaged. 
   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 actuation disk with respect to the retainer toward the case end. The preferred method would include a series of retainer tabs extending axially from one end of the retainer and notches which are adapted to engage the retainer tabs, 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. There are at least two, and preferably four, tabs extending outward to engage notches within the actuation disk. 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. 
   Further, the over-running clutch includes a sensor that detects the proximity of the actuation disk relative to the inner surface of the case end, and sends a corresponding signal to indicate that the over-running clutch is engaged or disengaged. 
   A lock indicator ring is mounted onto the actuation disk. The lock indicator ring includes at least one axially extending lobe that extends into one of the slots formed within the case end. The axial lobe includes at least one magnet mounted onto a distal end thereof. When the actuation disk is magnetically drawn toward the case end the distal end of the axial lobe comes into close proximity with the sensor. The sensor senses the presence of the magnet and sends a corresponding signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an over-running clutch of the present invention; 
       FIG. 2  is a sectional view taken along line  2 — 2  of  FIG. 1 ; 
       FIG. 3  is a enlarged portion of  FIG. 2  as indicated by circle  3  of  FIG. 2 ; 
       FIG. 4  is a perspective view of a lock indicator ring of the present invention having a plurality of magnets mounted onto axial lobes; 
       FIG. 5  is a perspective view of a lock indicator ring of the present invention having magnetic strips mounted onto axial lobes; 
       FIG. 6  is a perspective view of an electromagnetic coil mounted within a housing having a pair of sensors mounted therein; 
       FIG. 7  is a perspective view of a portion of a case end of the over-running clutch having the electromagnetic coil and housing mounted thereon; and 
       FIG. 8  is schematic diagram of the electrical circuit for the sensors of the present invention. 
   

   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  FIGS. 1–3 , and over-running clutch of the present invention is shown generally at  10 . The over-running clutch  10  includes an outer race  12  having an inner surface  14  that is rotatable about a first axis  16  and a case end  18 . An inner race  20  includes a cammed outer surface  22  coaxial with the 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 . 
   A plurality of rolling elements  26  are positioned within the gap  24 . Preferably, the rolling elements  26 , the inner race  20  and the outer race  12  are made from steel. Due to the high hertzian contact stresses experienced by the rolling elements  26 , the inner surface  14  of the outer race  12  and the outer surface  22  of the inner race  20 , and the rolling elements  26  are preferably hardened and ground, and made of steel. 
   The cammed outer surface  22  of the inner race  20  is defined by a plurality of ramp surfaces (not shown) that are formed at spaced apart locations along the outer surface  22 . The rolling elements  26  are positioned between the outer race  12  and the inner race  20  with one rolling element  26  being located at the center of each of the ramp surfaces of the inner race  20 . The rolling elements  26  have a diameter which is smaller than the gap  24  between the inner surface  14  and the midpoint of the ramp surfaces  23 , but greater than the gap  24  between the outer portions of the ramp surfaces  23  and the inner surface  14 . 
   A retainer  28  interconnects all of the rolling elements  26  and causes the rolling elements  26  to circumferentially move in unison with one another. The retainer  28  is rotatable about the first axis  16  with limited relative rotation with respect to the inner race  20 . The retainer  28  also includes a pair of retainer tabs  30  extending axially toward an inner surface  32  of the case end  18 . A distal end of each of the retainer tabs  32  is located adjacent the inner surface  32  of the case end  18  at a distance from the case end  18 . 
   A first biasing element  34  is mounted onto the retainer  28  to maintain the position of the retainer  28  with respect to the inner race  20  such that the rolling elements  26  are normally held in the middle of the ramp surfaces. An actuation disk  36  is disposed between the retainer  28  and the inner surface  32  of the case end  18 . The actuation disk  36  has an outer diameter and an inner diameter. The outer diameter of the actuation disk  36  includes notches  38  that engage the tabs  30  of the retainer  28 . In this way, the actuation disk  36  is linked to the retainer  28  such that rotational motion of the actuation disk  36  relative to the retainer  28  is prevented and axial motion of the actuation disk  36  relative to the retainer  28  is allowed. 
   A second biasing element  40  is disposed between the actuation disk  36  and the inner surface  32  of the case end  18  to bias the actuation disk  36  away from the case end  18  and toward the retainer  28 . Preferably, the second biasing element  40  is a wave spring. 
   Preferably, the first biasing element  34  is a centering spring supported by the inner race  20  and engaging the retainer  28  to keep the retainer  28  in position to keep the rolling elements  26  positioned at the center of the ramp surfaces of the inner race  20  thereby allowing the outer race  12  and the inner race  20  to rotate freely with respect to one other. The first biasing element  34  includes a plurality of small tangs (not shown) extending radially in or out to engage small notches (not shown) on the retainer  28 . The biasing force of the first biasing element  34  must be carefully calibrated for the over-running clutch  10 . The first biasing element  34  must provide enough force to move the retainer  28  and rolling elements  26  to the neutral position easily when the over-running clutch  10  is dis-engaged, but not so much force that friction between the actuation disk  36  and the case end  18  cannot overcome it to actuate the clutch  10 . 
   The over-running clutch  10  includes an actuator  42  to selectively overcome the second biasing element  40  and force the actuation disk  36  into contact with the case end  18 . Since the actuation disk  36  is free to move axially with respect to the retainer  28 , when the attractive force of the actuator  42  overcomes the force of the second biasing element  40 , the actuation disk  36  will move axially toward the inner surface  32  of the case end  18  until the actuation disk  36  and the inner surface  32  of the case end  18  come into contact with one another. When the actuation disk  36  and the case end  18  are brought into contact with one another, the relative rotational motion of the outer race  12  and the case end  18  with respect to the inner race  20  will frictionally be transferred to the actuation disk  36 . The actuation disk  36  is linked rotationally and circumferentially to the retainer  28 , therefore the rotational movement of the outer race  12  and the case end  18  will be transferred through the actuation disk  36  and to the retainer  28 . 
   Rotational movement of the retainer  28  with respect to the inner race  20  moves the rolling elements  26  along the ramp surfaces  23  until the rolling elements  26  are no longer positioned at the centers of the ramp surfaces  23 . Since the gap  24  is not large enough to accommodate the diameter of the rolling elements  26  when the rolling elements  26  move out of the centers of the ramp surfaces, the rolling elements  26  become wedged between the outer surface  22  of the inner race  20  and the inner surface  14  of the outer race  12 . This rotationally locks the inner race  20  and outer race  12  together. The ramp surfaces  23  and the interaction of the ramp surfaces  23  with the rolling elements  26  are described in detail in U.S. Pat. Nos. 5,927,456 and 5,924,510 which are both hereby incorporated by reference into the present application. 
   Preferably, the actuator  42  comprises an electromagnetic coil  44  held within a housing  46  mounted to an exterior structure (not shown). The case end  18  includes a plurality of partially circumferential slots  48  extending through the case end  18  and spaced radially about the case end  18 . When energized, the electromagnetic coil  44  produces a magnetic flux which is focused around the slots  48  and concentrated on the actuation disk  36 . When the magnetic flux passes through the actuation disk  36 , the actuation disk  36  is magnetically drawn toward the inner surface  32  of the case end  18 . Once the magnetic force of the electromagnetic coil  44  overcomes the force of the second biasing element  40 , the actuation disk  36  will start to move toward the inner surface  32  of the case end  18 . It is to be understood, that the present invention could be practiced with an actuator  42  of some other type. The actuation disk  36  could be moved through hydraulic or pneumatic means as well as through electromagnetic means. 
   When the actuator  42  is de-energized, the magnetic attraction of the actuation disk  36  to the inner surface  32  of the case end  18  dissipates. As this attraction dissipates, the second biasing element  40  quickly overcomes the dissipating magnetic attraction and forces the actuation disk  36  back away from the inner surface  32  of the case end  18 , thereby eliminating the frictional transfer of rotation to the actuation disk  36 . 
   Without a rotational force to pull the retainer  28  and rolling elements  26  out of the neutral position, the first biasing element  34  will force the retainer  28  back into the neutral position and the rolling elements  26  back into the middle of the ramp surfaces, thereby allowing the outer race  12  to rotate freely with respect to the inner race  20 , and un-locking the over-running clutch  10 . 
   Preferably, the housing  46  for the electromagnetic coil  44  is mounted to a stationary structure (not shown) and is located with respect to the case end  18  by a bearing  50 . The bearing  50  can be a ball, roller or journal bearing and will allow the electromagnetic coil  44  and the housing  46  to remain stationary. This will allow wiring to the electromagnetic coil  44  to be simplified because an electrical connection to a rotating body is not required. Any means suitable to allow relative rotational movement between the housing  46  and the exterior surface of the case end  18  is adequate. 
   The over-running clutch further includes a sensor  52  that detects the proximity of the actuation disk  36  relative to the inner surface  32  of the case end  18 , and sends a corresponding signal to indicate that the over-running clutch  10  is engaged or disengaged. The sensor  52  is mounted close to the radial mid-point of the coil face to balance the magnetic field sensing. A lock indicator ring  54  is mounted onto the actuation disk  36 . The lock indicator ring  54  includes at least one axially extending lobe  56  that extends into one of the slots  48  formed within the case end  18 . The axial lobe  56  includes at least one magnet  58  mounted onto a distal end  60  thereof. The sensor  52  is mounted onto the electromagnetic coil  44  adjacent the case end  18  and aligned with the slot  48  in the case end  18 . When the actuation disk  36  is magnetically drawn toward the case end  18 , the distal end  60  of the axial lobe  56  comes into close proximity with the sensor  52  on the electromagnetic coil  44 . The sensor  52  senses the presence of the magnet  58  mounted onto the distal end  60  of the axial lobe  56  and sends a corresponding signal. 
   Prefereably, the case end  18  includes a plurality of slots  48 , and the lock indicator ring  54  includes a plurality of axial lobes  56 . Referring to  FIGS. 4 and 5 , a lock indicator ring  54  having four axial lobes  56  is shown. The lock indicator ring  54  can include a plurality of magnets  58  mounted onto the distal end  60  of each of the axial lobes  56  and spaced therebout, as shown in  FIG. 4 . Alternatively, the lock indicator ring  54  can include a single magnetic strip  62  mounted to the distal end  60  of each axial lobe  56  extending along the length of the axial lobe  56 , as shown in  FIG. 5 . 
   Referring to  FIG. 6 , preferably, the sensor  52  comprises a pair of Hall effect sensors  52  spaced apart from one another and mounted within the electromagnetic coil  44 . The sensors  52  are aligned with opposite ends of one of the slots  48  formed within the case end  18 , as shown in  FIG. 7 . Preferably, the sensors  52  are unipolar Hall effect sensors. The sensors  52  should be spaced by at least the angular distance between opposite ends of one of the slots  48  in the case end  18 . The Hall effect sensors  52  are wired in parallel so that at least one of the sensors  52  is triggered at any time to provide a continuous signal even when gaps in the axial lobes  56  and the magnets  58  are in close proximity to the other Hall effect sensor  52 . Further, the outputs of the Hall effect sensors  52  can be tied together to a common output  64 . Referring to  FIG. 8 , a “pull-up” resistor  66  is used to bring the “high” signal up to the supply voltage. This circuit layout provides a fail safe normal “high” signal for the disengaged position, and results in a “low” signal whenever one or both of the Hall effect sensors  52  are activated. 
   The sensors  52  are placed on the electromagnetic coil at a position where the sensors  52  will not be automatically triggered whenever the electromagnetic coil  44  is energized. Further, the direction of the polarization of the electromagnetic coil  44  is such that the field generated by the electromagnetic coil  44  does not overcome the opposing fields of the magnets  58  on the axial lobes  56  of the lock indicator ring  54  to prevent the sensors  52  from triggering. 
   When the over-running clutch  10  is not actuated, the magnets  58  are shielded within the ferrous structure of the case end  18  and the magnetic fields are short-circuited and do not extend sufficiently forward toward the sensors  52 . When the over-running clutch  10  is actuated, the axial lobes  56  are moved forward such that the distal ends  60  of the axial lobes  56  extend beyond the slots  48  within the case end  18 , thereby exposing the sensors  52  to the magnetic fields of the magnets  58 . While the distance that the magnets  58  moves is minimal, only about 1.4 millimeters, the release of the shielding effect as the magnets  58  extend beyond the slots  48  in the case end  18  causes a dramatic increase in the magnetic field that the sensors  52  are exposed to. Therefore, the over-running clutch  10  can be manufactured with relatively wide tolerances, thereby reducing overall costs and making manufacturing easier, while providing a robust and reliable lock indication signal. 
   The foregoing discussion discloses and describes various aspects 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 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.