Abstract:
A dual disconnect differential assembly for four-wheel drive (4WD) vehicle is disclosed. This disconnect differential assembly connects/disconnects both output shafts of a differential assembly simultaneously from the respective universal joints of the drive assembly. Both output shafts are interconnected to provide simultaneous sliding along an axial direction. A clutch mechanism associated with the inboard side of each universal joint (which may be a constant velocity joint) and with the output shafts is provided for simultaneous connection and simultaneous disconnection of the output shafts from the outboard side of the universal joint. The dual disconnect differential assembly herein is simple, compact, and reliable. It overcomes the disadvantages associated with single axle disconnect mechanisms presently in use. It also provides a simpler, more compact, and more reliable dual disconnect differential mechanism than any such mechanism presently known.

Description:
[0001]    This application is a Continuation-in-part of pending application Ser. No. 09/950,574 filed on Sep. 13, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to differential disconnect drive assemblies or mechanisms, and in particular to dual disconnect drive assemblies, for four-wheel drive vehicles which can be operated in either a two-wheel drive mode or a four-wheel drive mode.  
           [0004]    2. Description of Related Art  
           [0005]    Four-wheel drive vehicles, which are operable in either a two-wheel drive mode or a four-wheel drive mode, have gained widespread popularity. Axle disconnect mechanisms, or differential disconnect mechanisms or assemblies for such vehicles are known.  
           [0006]    Commonly used disconnect mechanisms for four-wheel drive vehicles disconnect only one of the two output shafts on an axle assembly which is driven part time. This causes the pinion gears and the side gears of the differential to rotate due to back driving, although the differential case remains stationary. This is not compatible with speed-sensitive limited slip differentials. Also, single axle disconnect mechanisms may cause noise and wear and poor fuel economy due to rotation of the differential components while the vehicle is in two-wheel drive mode.  
           [0007]    Various dual disconnect differential assemblies or mechanisms have been proposed. These mechanisms in general have an unnecessary number of moving parts, are fairly complex, and would be suitable only for installation on relatively wide vehicles because of the space required. Earlier designs have interposed a clutch member between the side gear and the output shaft. None has achieved desirable commercial acceptance.  
         SUMMARY OF THE INVENTION  
         [0008]    This invention comprises a differential having first and second side gears, which are rotatable about a common transverse axis. Rotatable first and second output shafts are co-axial with the side gears and are arranged to drive a pair of respective wheels, and a universal joint (e.g., a constant velocity joint) is disposed between each output shaft and a respective wheel end. In accordance with this invention, a clutch mechanism is used for placing each output shaft simultaneously into or simultaneously out of driving engagement with the inboard side of an associated universal joint. An actuator is used to slidably and concurrently move the output shafts between the clutch engaging position and the clutch disengaging position with respect to the universal joint to thereby disconnect the output shaft from the associated axle shafts and joint assembly.  
           [0009]    In the preferred embodiment, the output shafts have clutch members for engaging the clutch members of the respective first and second universal joints, with the output shafts being simultaneously slidable in a first direction to a clutch engaging position and simultaneously slidable in a second direction to a clutch disengaging position. The output shafts are interconnected to provide simultaneous sliding movement.  
           [0010]    A preferred dual disconnect differential assembly according to the invention includes, as axially engageable clutch members, a spline interface connection between the first and second universal joints and the respective first and second output shafts. A biasing means is provided for biasing the output shafts to a clutch disengaging position. The vehicle is in two-wheel drive mode when the clutch is disengaged and in four-wheel drive mode when the clutch is engaged. An actuator causes sliding movement of the interconnected output shafts to translate the shafts into the disengaged position.  
           [0011]    Another aspect of the clutch mechanism of the invention provides a pair of split-spline teeth on both the output shafts and the respective universal joints to reduce the travel distance required to engage/disengage the dual axle disconnect system.  
           [0012]    The differential assembly of the present invention possesses several advantages, including greater fuel economy, less wear, and less noise compared to previously known disconnect mechanism in which only a single output shaft and its axle shaft are disengaged from driving engagement with a differential when two-wheel drive mode is selected. Advantages of the present invention compared to previously known dual disconnect differential assemblies include a more robust design without increased packaged size, fewer parts and greater compactness, which makes it possible to utilize the present dual disconnect drive mechanism on any size vehicle, including a sub-compact automobile. This makes it possible to offer four-wheel drive on smaller vehicles, including sub-compact automobiles, which have not previously had optional four-wheel drive because of the space requirements of presently known dual disconnect mechanism.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a sectional plan view of the invention according to a preferred embodiment of the invention.  
         [0014]    [0014]FIG. 2 is an enlarged sectional plan view of the invention according to a preferred embodiment of FIG. 1.  
         [0015]    [0015]FIG. 3 is a partial sectional plan view according to the invention according to a second embodiment of the invention. In this embodiment, the return spring  42  is not required.  
         [0016]    [0016]FIG. 4 is a perspective view of the interconnecting collar connecting the two output shafts of the second embodiment.  
         [0017]    [0017]FIG. 5 is a sectional plan view of the invention according to a second preferred embodiment of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    This invention will now be described in detail with reference to the best mode and preferred embodiments thereof.  
         [0019]    Referring now to FIG. 1, a dual disconnect differential assembly (or mechanism) according to this invention is shown for a front axle of a four-wheel drive ( 4 WD) vehicle having a fall-time rear axle and a part-time front axle.  
         [0020]    The differential assembly in general is driven by a longitudinally extending pinion shaft (or input shaft) not shown, which in turn may be driven by a drive shaft (not shown) which extends longitudinally from a vehicle transmission. The pinion shaft may engage a ring gear (not shown), which is affixed (e.g., bolted) to a differential case  12 . Differential case  12  is rotatably mounted in a differential housing  14  by means of bearings  15 . Differential case  12  and the ring gear affixed thereto rotate about a transverse horizontal axis ‘x-x’, which is the axis of output shafts  24 ,  25 .  
         [0021]    The differential used in the practice of this invention may further include a differential cross pin  16 , and pinion gears  18  which are rotatably mounted with respect to cross pin  16 . The differential further includes first (or left-hand) and second (or righthand) side gears  20  and  21 , respectively (see FIGS. 1, 2, and  3 ). Side gears  20  and  21  are coaxial and rotate about a common transverse axis, which is also the common axis of the aforementioned output shafts  24 ,  25 .  
         [0022]    The outboard ends of the output shafts  24 ,  25  are provided with universal joints  50 ,  60  (e.g. constant velocity joints) between the output shafts  24 ,  25  and the respective wheel ends.  
         [0023]    In accordance with the present invention, a clutch mechanism is provided between the universal joints  50 ,  60  have respective output shafts  25 ,  24  in the form of splines (for example, splines  25   a ,  50   a ), as best seen in FIG. 2. These splines are formed on central bores of respective inner members at the inboard side of each universal joint  50 ,  60 .  
         [0024]    As with the conventional differential drive assembly, the dual disconnect axle assembly  14  of this invention includes a coaxial first (or left-hand) output shaft  24  and a second (or right-hand) output shaft  25 . These output shafts  24 ,  25  extend transversely and are coaxial with side gears  20 ,  21 . These output shafts  24 ,  25  extend from inboard ends near cross pin  16  to outboard ends, which extend outside the differential housing. Splines (e.g. splines  25   a ,  50   a ) are provided at the inboard ends of universal joints  50 ,  60  for selectively driving the same and which may be conventional (e.g., universal joints) provided at respective outboard ends of output shafts  24 ,  25  and extend transversely outwardly to wheels (not shown) at the sides of the vehicle.  
         [0025]    According to one important aspect of this invention, the first and second output shafts  24 ,  25  are interconnected and axially slidable together as a unit. In other words, the present invention preferably provides a linking member  29  in the form of a linking rod or other suitable member that extends through the differential assembly to connect the two output shafts  24 ,  25 . With this arrangement, the invention provides simultaneous axial movement of the output shafts to thereby mutually disconnect the first and second output shafts  24 ,  25  from the first and second universal joints  50 ,  60 . In the embodiment of FIG. 1, the linking rod  29  passes through the cross pin  16 . In the alternate embodiment of FIG. 3, the linking member  129  takes the form of a connecting sleeve that connects the output shafts  24 ,  25 . In the arrangement of FIG. 3, the cross pin  16  passes through the connecting sleeve  129  at apertures  130 . In both illustrated designs, the two driven output shafts  24 ,  25  are securely linked together to provide mutual linear sliding movement between the clutch engaged and disengaged positions.  
         [0026]    The dual disconnect axle assembly  14  of this invention includes a clutch mechanism for simultaneously placing output shafts  24 ,  25  either into or out of driving engagement with respective universal joints  50 ,  60 . The splines between respective output shafts and the universal joints form part of this clutch assembly or mechanism.  
         [0027]    The entire set of clutch members, including internally-splined inner member  50  of the universal joints and externally-splined output shafts  24 ,  25 , are shown in clutch disengaging position in FIG. 1, being the normal position. Upon actuation, as will be described subsequently, the axially slidable output shafts  24 ,  25  slide to the left as seen in FIG. 1 into a clutch engaging position, in which clutch members or splines on respective universal joints  50 ,  60  are in engagement with respective splines on respective output shafts  24 ,  25 . Output shafts  24 ,  25  rotate with respective universal joints  50 ,  60  when the clutch mechanism is in the clutch engaging position, and rotate independently of the respective universal joints  50 ,  60  when the clutch mechanism is in the clutch disengaging position.  
         [0028]    A compression spring  42  serves as biasing means to urge the axially slidable output shafts  24 ,  25  to clutch disengaging position, i.e., to the right as seen in FIG. 1. Spring  42  abuts the first or left-hand output shaft  24 .  
         [0029]    To actuate the clutch mechanism, a clutch actuator  40  may be provided as a shift fork having a bifurcated end portion which is received in groove  38  of clutch collar  36  fixedly provides on one of the output shafts. The shift fork  40  may be actuated by known means  41 , e.g., by electrical (which is preferred) or by hydraulic, pneumatic, vacuum, or mechanical means. Actuation may be initiated either automatically or by a manual operator, such as a manual or pedal control in the vehicle cab.  
         [0030]    The output shafts  24 ,  25  and collar  36  are normally in clutch disengaging position, i.e., to the right as seen in FIG. 1. The vehicle is in two-wheel drive (2WD) mode when the clutch is disengaged. To engage the clutch mechanism and place the vehicle in four-wheel drive (4WD) mode, clutch actuator  40  moves clutch collar  36  to the left as seen in FIG. 1 against the bias of compression spring  42 . Clutch collar  36  pushes the output shafts  24 ,  25  to the left against the bias of spring  42 , thereby placing the clutch members or splines on respective driven output shafts  24 ,  25  in engagement with respective clutch members or splines (e.g., splines  52   a ) on respective universal joints  50 ,  60 . With the clutch mechanism thus engaged, the output shafts  24 ,  25  are constrained to rotate at the same speeds as respective universal joints  50 ,  60  and power is transmitted to the respective wheel ends (not shown) through the joints  50 ,  60 . When the need for four-wheel drive no longer exists, clutch actuator  40  is moved to the right. This also slides clutch collar  36  to the right. Compression spring  42  then pushes output shafts  24 ,  25  to the right, i.e., to the clutch disengaging position, to return the vehicle to two-wheel drive mode.  
         [0031]    The drawings herein show a differential assembly for a front axle of a vehicle. Most current vehicles which have four-wheel drive have a full-time rear axle and a part-time front axle. However, some recent four-wheel drive vehicles have a full-time front axle and a part-time rear axle. The differential assembly of this invention can be used on either the front axle or the rear axle, whichever axle is the part-time axle.  
         [0032]    The compression spring  42  (or other biasing means) is normally biased toward the clutch disengaging position, which results in disengagement of the part-time axle, since it is normally preferred to operate in two-wheel drive mode with the part-time axle disengaged except when driving conditions call for four-wheel drive operation. However, this spring can be biased toward clutch engaging position if desired. Other biasing means, as for example, an air spring, can be used in place of the compression spring shown if desired.  
         [0033]    Further, the biasing means can be dispensed with entirely provided that some means, such as magnets on the relatively slidable members. Such magnets, if used, must not be so strong as to prevent or impede relative rotation between adjacent axially slidable members. Other mechanical mechanisms which function to shift the output shafts  24 ,  25  to the clutch disengaging position are also contemplated herein, and the second embodiment shown in FIG. 3.  
         [0034]    It is possible to use a solenoid operator, e.g., an annular solenoid operator surrounding the output shafts  24 , and, in that case, to dispense with collar  36  if desired. However, the illustrated apparatus, including a collar  36  and a shift fork  40 , is preferred since this gives more versatility both as to type and location of the actuator.  
         [0035]    It is also possible to use a spider (which typically including a ring at its center with a plurality of radially extending arms extending outwardly from the ring) in place of the cross pin  16  if desired.  
         [0036]    An alternate embodiment of the present invention is illustrated in FIG. 5, in which a clutch mechanism is provided between the universal joints  250 ,  260  and respective output shafts  225 ,  224  in the form of splines (for example, splines  25   a ,  50   a  in FIG. 2). These splines are formed on central bores of respective inner members at the inboard side of each universal joint  250 ,  260 .  
         [0037]    As with the conventional differential drive assembly, the dual disconnect axle assembly of this invention includes a coaxial first (or left-hand) output shaft  224  and a second (or right-hand) output shaft  225 . These output shafts  224 ,  225  extend transversely and are coaxial with side gears  220 ,  221 . These output shafts  224 ,  225  extend from inboard ends near cross pin  216  to outboard ends, which extend outside the differential housing. Splines (e.g. splines  25   a ,  50   a  in FIG. 2) are provided at the inboard ends of universal joints  250 ,  260  for selectively driving the same and which may be conventional (e.g., universal joints) provided at respective outboard ends of output shafts  224 ,  225  and extend transversely outwardly to wheels (not shown) at the sides of the vehicle.  
         [0038]    According to one important aspect of this invention, the first and second output shafts  224 ,  225  are interconnected and axially slidable together as a unit. In other words, the present invention preferably provides a linking member  229  in the form of a linking rod or other suitable member that extends through the differential assembly to connect the two output shafts  224 ,  225 . With this arrangement, the invention provides simultaneous axial movement of the output shafts to thereby mutually disconnect the first and second output shafts  224 ,  225  from the first and second universal joints  250 ,  260 . In the embodiment of FIG. 5, the linking rod  229  passes through the cross pin  216 . In the alternate embodiment of FIG. 3, the linking member takes the form of a connecting sleeve that connects the output shafts  24 ,  25 . In the arrangement of FIG. 3, the cross pin passes through the connecting sleeve at apertures  130 . In the illustrated designs, the two driven output shafts  224 ,  225  are securely linked together to provide mutual linear sliding movement between the clutch engaged and disengaged positions.  
         [0039]    The dual disconnect axle assembly of this invention includes a clutch mechanism for simultaneously placing output shafts  224 ,  225  either into or out of driving engagement with respective universal joints  250 ,  260 . The splines between respective output shafts and the universal joints form part of this clutch assembly or mechanism.  
         [0040]    The entire set of clutch members, including internally-splined inner member  250  of the universal joints and externally-splined output shafts  224 ,  225 , are shown in clutch disengaging position in FIG. 5, being the normal (default) position. Upon actuation, as will be described subsequently, the axially slidable output shafts  224 ,  225  slide to the left as seen in FIG. 5 into a clutch engaging position, in which clutch members or splines on respective universal joints  250 ,  260  are in engagement with respective splines on respective output shafts  224 ,  225 . Output shafts  224 ,  225  rotate with respective universal joints  250 ,  260  when the clutch mechanism is in the clutch engaging position, and rotate independently of the respective universal joints  250 ,  260  when the clutch mechanism is in the clutch disengaging position.  
         [0041]    A compression spring  242  serves as biasing means to urge the axially slidable output shafts  224 ,  225  to clutch disengaging position, i.e., to the right as seen in FIG. 5. Spring  242  abuts the first or left-hand output shaft  224 .  
         [0042]    To actuate the clutch mechanism, a clutch actuator (not shown) may be provided as a shift fork having a bifurcated end portion which is received in groove  238  of clutch collar  236  fixedly provides on one of the output shafts. The shift fork may be actuated by known means, e.g., by electrical (which is preferred) or by hydraulic, pneumatic, vacuum, or mechanical means. Actuation may be initiated either automatically or by a manual operator, such as a manual or pedal control in the vehicle cab.  
         [0043]    In accordance with the alternate embodiment of FIG. 5, the dual disconnect axle assembly is further provided with means to enable a locking differential. To wit, the clutch collar  236  is provided with first locking teeth  239  at its left-most end facing the differential case  212  and the differential case is likewise provided with second locking teeth  213  at the trunnion facing the clutch collar  236  to thereby provide a type of dog clutch between the collar  239  and the case  213 . When the clutch collar is shifted to its extreme left-most position shown in FIG. 5, the first locking teeth  239  engage the second locking teeth  213  provided on the differential case to thereby lock the output shafts  224 ,  225  to the differential case  212 .  
         [0044]    With the embodiment of FIG. 5, the clutch collar  236  may be shifted to a first position where the splines of output shafts mate with the splines of the universal joints by means of the compression spring  237  located inside the collar  236 , and the collar  236  may be further shifted to a position where the teeth  239  engage the teeth  213  of the differential case to rotationally lock the output shafts to the differential case (i.e., locking differential).  
         [0045]    The present invention provides a simple and reliable mechanism for simultaneous differential connect and simultaneous differential disconnect. In other words, both output shafts  24 ,  25  are simultaneously connected or disconnected from their respective universal joints  50 ,  60  in the apparatus of this invention. The novel dual disconnect differential assembly herein avoids the known disadvantages of single shaft disconnect mechanism, such as back drive, as has been discussed earlier.  
         [0046]    The dual disconnect differential assembly of this invention is also compact. This makes part-time, dual disconnect four-wheel drive for compact and sub-compact vehicles possible.  
         [0047]    Further, the assembly may be modified to provide a locking differential to selectively lock the output shafts to the differential case.  
         [0048]    While this invention has been described in detail with reference to the preferred embodiments thereof, it shall be understood that various modifications (including those specifically discussed above and others) can be made without departing from the scope and spirit of this invention.