Abstract:
A dual disconnect differential assembly for four-wheel drive (4WD) vehicle is disclosed. This disconnect differential assembly connects/disconnects both axle shafts of a differential assembly simultaneously from the side gears of the differential assembly. Both axle shafts are interconnected to provide simultaneous sliding along an axial direction. A clutch mechanism associated with the two differential side gears (which may be otherwise conventional) and with the axle shafts is provided for simultaneous connection and simultaneous disconnection of the axle shafts. 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:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     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. 
     2. Description of Related Art 
     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. 
     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. 
     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 axle shaft. None has achieved desirable commercial acceptance. 
     SUMMARY OF THE INVENTION 
     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 a clutch mechanism is used for placing the output shafts simultaneously into or simultaneously out of driving engagement with the respective side gears. An actuator is used to slidably and concurrently move the driven axles between the clutch engaging position and the clutch disengaging position. 
     The driven axles have clutch members for engaging the clutch members of the respective first and second side gears, with the driven axles 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 driven axles are interconnected to provide simultaneous sliding movement. 
     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 side gears and the respective first and second driven axles. A biasing means is provided for biasing the driven gears 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 driven axles to translate the axles into the disengaged position. 
     Another aspect of the clutch mechanism of the invention provides a pair of split spline teeth on both the axle shaft and the side gear to reduce the travel distance required to engage/disengage the dual axle disconnect system. 
     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 shaft/gear 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 
     FIG. 1 is a sectional plan view of the invention according to a preferred embodiment of the invention. 
     FIG. 2 is an enlarged sectional plan view of the invention according to a preferred embodiment of FIG.  1 . 
     FIG. 3 is a partial sectional plan view according to the invention according to a second embodiment of the invention. 
     FIG. 4 is a perspective view of the interconnecting collar connecting the two driven axles of the second embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This invention will now be described in detail with reference to the best mode and preferred embodiments thereof. 
     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 (4WD) vehicle having a full-time rear axle and a part-time front axle. 
     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, which is the axis of output shafts  24 ,  25 . 
     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 right-hand) 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 axle shafts  24 ,  25 . 
     Side gears  20 ,  21  have respective clutch members in the form of splines  22 ,  23 , respectively, as best seen in FIG.  2 . These splines are formed on central bores of respective side gears  20 ,  21  near the left-hand ends thereof, at the outboard end of left-hand side gear  20  and at the inboard end of right-hand side gear  21 . 
     The dual disconnect differential assembly  10  of this invention further 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  26 ,  27  are provided at the inboard ends of output shafts for driving the same. Joints or flanges  28 , which may be conventional (e.g., universal joints), are provided at respective outboard ends of output shafts  24 ,  25  and extend transversely outwardly to wheels (not shown) at the sides of the vehicle. 
     According to one important aspect of this invention, the first and second axle 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 axle shafts  24 ,  25 . With this arrangement, the invention provides simultaneous axial movement of the axle shafts to thereby mutually disconnect the first and second axle shafts  24 ,  25  from the first and second side gears  20 ,  21 . In the embodiment of FIGS. 1 and 2, the linking rod 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 axle 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 axle shafts  24 ,  25  are securely linked together to provide mutual linear sliding movement between the clutch engaged and disengaged positions. 
     The dual disconnect differential assembly  10  of this invention includes a clutch mechanism for simultaneously placing both output shafts  24  either into or out of driving engagement with respective side gears  20 ,  21 . The splines  22 ,  23  on respective side gears  20 ,  21  form part of this clutch assembly or mechanism. 
     Driven splines  26 ,  27  are fixedly provided or otherwise formed on respective output shafts  24 ,  25 . Internal splines  32  on the side gears  20 ,  21 , and external splines  26 ,  27  on the output shafts  24 ,  25 , prevent relative rotation while permitting axial sliding movement of the driven gears. Thus, side gears  20 ,  21  rotate with the respective output shafts  24 ,  25  in the engaged position. 
     The entire set of clutch members, including internally-splined side gears  20 ,  21  and externally-splined axle 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 axle shafts  24 ,  25  slide to the left as seen in FIG. 1 into a clutch engaging position, in which clutch members or splines  22 ,  23  on respective side gears  20 ,  21  are in engagement with respective splines  26 ,  27  on respective axle shafts  24 ,  25 . Output shafts  24 ,  25  rotate with respective side gears  20 ,  21  when the clutch mechanism is in the clutch engaging position, and rotate independently of the respective side gears  20 ,  21  when the clutch mechanism is in the clutch disengaging position. 
     A compression spring  42  serves as biasing means to urge the axially slidable axle 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 . 
     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 axle 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. 
     The axle 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 axle shafts  24 ,  25  to the left against the bias of spring  42 , thereby placing the clutch members or splines  26 ,  27  on respective driven axle shafts  24 ,  25  in engagement with respective clutch members or splines  22 ,  23  on respective side gears  20 ,  21 . With the clutch mechanism thus engaged, the axle shafts  24  are constrained to rotate at the same speeds as respective side gears  20 ,  21  and power is transmitted to the respective wheel ends (not shown) through the joint  28 . 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 axle shafts  24 ,  25  to the right, i.e., to the clutch disengaging position, to return the vehicle to two-wheel drive mode. 
     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 is the part-time axle. 
     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. 
     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 driven axle shafts  24 ,  25  to the clutch disengaging position are also contemplated herein. 
     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. 
     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. 
     While driven gears  30  have external splines for such purposes extending over their entire length are illustrated, it will be apparent that the axial length of the driven gears may be longer than that herein illustrated, and that these external splines need not extend over the entire length. In such case, the splined portion would be to the right as seen in FIG.  1 . This is ordinarily not preferred because it would require left and right driven gears which are not identical to each other in most cases, except where the axial length of the splined portion is exactly one-half the total axial length of the driven gear. 
     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 side gears  20 ,  21  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. 
     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. 
     The two side gears  20 ,  21  are free to rotate at different speeds, whether the output shafts  24  are engaged with or disengaged from the respective side gears  20 ,  21 . However, if desired, a differential assembly for a part-time axle as herein illustrate can be further provided with a differential lockout mechanism (which may be conventional) if desired. 
     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.