Vehicle drive system including drive mode-shifting mechanism for shifting between two-wheel drive and four-wheel drive

Abstract

A vehicle drive system includes a compact drive mode-shifting mechanism that is mounted in the final drive gearset of a vehicle. The drive mode-shifting mechanism includes a first shaft, a second shaft, and a clutch assembly. The first shaft forms an input shaft for the differential for a pair of wheels, the second shaft transmits engine power and the clutch assembly connects and disconnects the first and second shafts to one another to effect either the two-wheel-drive mode or the four-wheel-drive mode. The first shaft has an outer surface provided with a first spline, the second shaft has an outer surface provided with a second spline, and said clutch assembly includes an axially movable shifting member provided with an internal spline. The shifting member is movable between a first position in which the internal spline on the shifting member is in engagement with the first spline on the first shaft and the second spline on the second shaft to achieve the four-wheel-drive more and a second position in which the internal spline on the shifting member is in engagement with the first spline on the first shaft and is out of engagement with the second spline on the second shaft to achieve the two-wheel-drive mode.

1. A vehicle drive system switchable between two-wheel-drive mode and a four-wheel-drive mode comprises:
 a transmission;  
 a housing in which is disposed a differential gear connected to a pair of wheels and a drive-mode-shifting mechanism;  
 the drive-mode-shifting mechanism including a first shaft forming an input shaft for the differential gear, a second shaft for transmitting power from the transmission, and a clutch assembly for connecting the first and second shafts during the four-wheel-drive mode and for disconnecting the first and second shafts during the two-wheel-drive mode; and  
   the clutch assembly being operated by an electric motor.    
 
     
     
       2. A vehicle drive system according to  claim 1 , including a drive axle extending between the transmission and the housing. 
     
     
       3. A vehicle drive system according to  claim 1 , wherein said first and second shafts are mounted coaxially. 
     
     
       4. A vehicle drive system according to  claim 1 , wherein said firm shaft has an outer surface provided with a first spline, and second shaft has an outer surfaces provided with a second spline, and said clutch assembly includes an axially movable shifting member provided with an internal spline, said shifting member being movable between a first position in which the internal spline on the shifting member is in engagement with the first spline on the first shaft and the second spline on the second shaft to achieve the four-wheel-drive mode and a second position in which the internal spline on the shifting member is in engagement with the first spline on the first shaft and is out of engagement with the second spline on the second shaft to achieve the two-wheel-drive mode. 
     
     
       5. A vehicle drive system according to  claim 4 , including a shifting device for moving the shifting member between the first and second positions. 
     
     
       6. A vehicle drive system according to  claim 5 , wherein the shifting device includes an element fixed to the shifting member, a rack to which is fixed the element, and a gear for moving the rack. 
     
     
       7. A vehicle drive system according to  claim 6 , including a switch-depressing portion provided on said element, and a switch operated by the switch-depressing portion during movement of said element. 
     
     
       8. A vehicle drive system for a vehicle that includes four wheels and is switchable between a two-wheel-drive mode in which only two of the wheels are driven and a four-wheel-drive mode in which all four of the wheels are driven comprising:
 a transmission;  
 a differential gear;  
 a drive mode-shifting mechanism positioned between the transmission and the differential gear for shifting between the two-wheel-drive mode and the four-wheel-drive mode, the drive mode-shifting mechanism including a first shaft, a second shaft and a clutch assembly for connecting the first shaft and the second shaft during the four-wheel-drive mode and for disconnecting the first shaft and the second shaft during the two-wheel-drive mode;  
 the clutch assembly being operated by an electric motor to effect the shifting between the two- wheel - drive mode in which the first shaft and the second shaft are disconnected and the four - wheel - drive mode in which the first shaft and the second shaft are connected;  and  
 the vehicle drive system being devoid of a differential between the transmission and the drive mode-shifting mechanism.  
 
     
     
       9. A vehicle drive system according to  claim 8 , including a housing which houses the drive mode-shifting mechanism and the differential gear. 
     
     
       10. A vehicle drive system according to  claim 8 , wherein said first and second shaft are mounted coaxially. 
     
     
       11. A vehicle drive system according to  claim 8 , including a drive axle extending from the transmission, and a yoke connected a the drive axle and to an end of the second shaft opposite the first shaft for permitting the drive axle and the second shaft to pivot relative to our another. 
     
     
       12. A vehicle drive system according to  claim 8 , wherein said first shaft forms an input shaft for the differential gear. 
     
     
       13. A vehicle drive system according so  claim 8 , wherein said first shaft has an outer surface provided with a first spline, said second shaft has an outer surface provided with a second spline, and said clutch assembly includes an axially movable shifting member provided with an internal spline, said shifting member being movable between a first position in which the internal spline on the shifting member is in engagement with the first spline on the first shaft and the second spline or the second shaft to achieve the four-wheel-drive mode and a second position in which the internal spline on the shifting member is in engagement with the first spline on the first shaft and is out of engagement with the second spline on the second shaft to achieve the two-wheel-drive mode. 
     
     
       14. A vehicle drive system according to  claim 13 , including a shifting device for moving the shifting member between the first and second positions. 
     
     
       15. A vehicle drive system according to  claim 14 , wherein the shifting device includes an element fixed to the shifting member, a rack to which is fixed the element, and a gear for moving the rack. 
     
     
       16. A vehicle drive system according to  claim 15 , including a switch-depressing portion provided on said element, and a switch operated by the switch-depressing portion during movement of said element. 
     
     
       17. A vehicle drive system switchable between a two-wheel-drive mode and a four-wheel-drive mode, comprising:
 a drive axle;  
 a differential gear connectable to a pair of wheels;  
 a drive mode-shifting mechanism for shifting between the two-wheel-drive mode and the four-wheel-drive mode, the drive mode-shifting mechanism including a first shaft forming an input shaft of the differential gear, a second shaft for transmitting power, and a clutch assembly for connecting the first shaft and the second shaft during the four-wheel-drive mode and for disconnecting the first shaft and the second shaft during the two-wheel-drive mode;  
 the clutch assembly including a shifting member axially shifted through operation of an electric motor to effect the switching between the four- wheel - drive mode and the two - wheel - drive mode;  and  
 a yoke connected to the drive axle and an end of the second shaft opposite the first shaft for permitting the drive axle and the second shaft to pivot relative to one another.  
 
     
     
       18. A vehicle drive system according to  claim 17 , wherein said first and second shafts are mounted coaxially. 
     
     
       19. A vehicle drive system according to  claim 17 , wherein said first shaft has an outer surface provided with a first spline, said second shaft has an outer surface provided with a second spline, and said clutch assembly includes an axially movable shifting member being provided with an internal spline, said shifting member being movable between a first position in which the internal spline on the shifting member is in engagement with the first spline on the first shaft and the second spline an the second shaft to achieve the four-wheel-drive mode and a second positions in which the internal spline on the shifting member is in engagement with the first spline an the first shaft and is out of engagement with the second spline on the second shaft to achieve the two-wheel-drive mode. 
     
     
       20. A vehicle drive system according to  claim 19 , including a shifting device for moving the shifting member between the first and second positions, said shifting device including as element fixed to the shifting member, a rack to which said element is fixed, and a gear for moving the rack. 
     
     
       21. A vehicle drive system according to  claim 1 , including a first spline directly formed on an outer surface of the first shaft, the clutch assembly including an axially movable shifting member that is axially moved through operation of the electric motor, the shifting member possessing an inner surface with an internal spline formed on the inner surface of the shifting member, the internal spline of the shifting member being engageable with the first spline of the first shaft. 
     
     
       22. A vehicle drive system according to  claim 1 , wherein the clutch assembly includes an axially movable shifting member, the electric motor being operatively connected to an element which engages the shifting member to axially move the shifting member during operation of the electric motor. 
     
     
       23. A vehicle drive system according to  claim 22 , wherein the element engaging the shifting member is a fork. 
     
     
       24. A vehicle drive system according to  claim 1 , wherein the four- wheel - drive mode is electrically detected.   
     
     
       25. A vehicle drive system according to  claim 8 , including a first spline directly formed on an outer surface of the first shaft, the clutch assembly including a shifting member possessing an inner surface with an internal spline formed directly on the inner surface of the shifting member, the internal spline of the shifting member being engageable with the first spline of the first shaft. 
     
     
       26. A vehicle drive system according to  claim 25 , wherein the internal spline of the shifting member engages the first spline of the first shaft during both the four- wheel - drive mode and the two - wheel - drive mode.   
     
     
       27. A vehicle drive system according to  claim 25 , wherein the electric motor is operatively connected to an element which engages the shifting member to axially move the shifting member during operation of the electric motor. 
     
     
       28. A vehicle drive system according to  claim 8 , wherein the four- wheel - drive mode is electrically detected.   
     
     
       29. A vehicle drive system according to  claim 17 , including a first spline directly formed on an outer surface of the first shaft, the shifting member possessing an inner surface with an internal spline formed directly on the inner surface of the shifting member, the internal spline of the shifting member being engageable with the first spline of the first shaft. 
     
     
       30. A vehicle drive system according to  claim 29 , wherein the internal spline of the shifting member engages the first spline on the first shaft during both the four- wheel - drive mode and the two - wheel - drive mode.   
     
     
       31. A vehicle drive system according to  claim 17 , wherein the electric motor is operatively connected to an element engaging the shifting member to axially move the shifting member during operation of the electric motor. 
     
     
       32. A vehicle drive system according to  claim 17 , wherein the four wheel- drive - mode is electrically detected.   
     
     
       33. A vehicle drive system switchable between two- wheel - drive mode and a four - wheel - drive mode comprises:      a transmission;        a housing in which is disposed a differential gear connected to a pair of wheels and a drive - mode - shifting mechanism;        the drive - mode - shifting mechanism including a first shaft forming an input shaft for the differential gear, a second shaft for transmitting from the transmission, and a clutch assembly for connecting the first and second shafts during the four - wheel - drive mode and for disconnecting the first and second shafts during the two - wheel - drive mode;        the first shaft having an outer surface with a first spline directly formed on the outer surface of the first shaft;        the clutch assembly including an axially movable shifting member having an inner surface with an internal spline formed on the inner surface of the shifting member, the internal spline of the shifting member and the first spline of the first shaft engaging one another in both the two - wheel - drive mode and the four - wheel - drive mode;        the shifting member being engaged by an element which is operatively connected to an electric motor so that operation of the electric motor axially moves the shifting member between one position in the two - wheel - drive mode in which the first and second shafts are disconnected and another position in the four - wheel - drive mode in which the first and second shafts are connected to one another by the shifting member.     
     
     
       34. A vehicle drive system according to  claim 33 , wherein the four- wheel - drive mode is electrically detected.