Abstract:
A shifting device of the automatic transfer includes a rack formed on a sleeve in the lengthwise direction of an output shaft, and a rotation torque supplying means is meshed to the rack, for linearly moving the sleeve over the output shaft. The response characteristics are improved when shifting from AUTO mode to LOW mode and vice versa, and the number of the involved components and the number of the assembling steps are decreased, thereby minimizing the manufacturing cost.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a transfer case for a 4-wheel-drive power train, and more particularly, to a shifting device for an electronically controlled transfer case.  
         BACKGROUND OF THE INVENTION  
         [0002]    A 4-wheel drive (4WD) vehicle exerts a driving force on all four wheels. Thus, the engine distributes power to both front and rear axles to maintain traction under all conditions. 4WD systems are classified as either part time or full time 4WD systems.  
           [0003]    In a part time 4WD system, the vehicle operates in a 2-weel driving mode during normal conditions. However, upon encountering rough terrain or adverse weather conditions, a 4-wheel drive mode is engaged by using a 4WD transfer case to transfer a strong driving force or torque to all 4 wheels. In a full time 4WD system, all four wheels exert the driving force. Therefore, a full time 4WD system ensures stable traction both during normal conditions and adverse weather conditions, and therefore, many expensive vehicles come equipped with a 4WD transfer case.  
           [0004]    Recently-built full time 4WD systems include an AUTO mode and a LOW mode. In the AUTO mode, the revolution differences between the front wheels and the rear wheels are electronically controlled by a multi-plate clutch, which engages the 2WD to 4WD, and vice versa. When maximum driving force or torque is required to maneuver the vehicle out of rough terrain or pull another vehicle, the system is shifted to the LOW mode.  
           [0005]    Conventional transfer cases, however, have complicated mechanisms for shifting from the AUTO mode to the LOW mode and vice versa. Further, the number of the required components is large, and the manufacturing cost is high.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a shifting device for an automatic transfer case, in which the response characteristics are improved when shifting from an AUTO mode to a LOW mode and vice versa. The number of components required and the number of assembly steps are decreased, thereby curtailing the manufacturing cost.  
           [0007]    In accordance with an embodiment of the present invention, a shifting device for an automatic transfer case comprises a rack formed on a sleeve in the longitudinal direction of an output shaft, and a rotation torque supplying means meshed to the rack, for linearly moving the sleeve on the output shaft. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    For fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings in which:  
         [0009]    [0009]FIG. 1 illustrates a typical automatic transfer case;  
         [0010]    [0010]FIG. 2 illustrates in detail the typical automatic transfer case of FIG. 1;  
         [0011]    [0011]FIG. 3 illustrates an automatic transfer case of the present invention, in which the automatic transfer shifting device is embodied; and  
         [0012]    [0012]FIG. 4 is a side view of the shifting device of FIG. 3. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    The present invention will be described in detail referring to the attached drawings. Like components of the conventional automatic transfer case and the present invention will be assigned identical reference numerals and part names.  
         [0014]    [0014]FIGS. 1 and 2 illustrate a typical transmission used on electronically-controlled full time 4WD vehicles.  
         [0015]    As shown in these drawings, the transfer case includes an input shaft  100  for receiving the power from a transmission, an output shaft  102  disposed coaxially with the input shaft  100 , and connected to a rear driver shaft, a sun gear  104  installed on the input shaft  100 , and a planetary carrier  106  meshed to the sun gear  104 , a sleeve  108  for sliding on the output shaft  102  so as to shift from a direct connection status between the input/output shafts  100  and  102  to a direct connection status between the planetary carrier  106  and the output shaft  102 , a slide manipulation device for making the sleeve  108  slide on the output shaft, a multi-plate clutch  112  with a hub  110  spline-coupled onto the output shaft  102 , a driving sprocket  116  directly connected to a retainer  114  of the multi-plate clutch  112 , an electronic coil  118  for activating the multi-plate clutch  112 , and a driven sprocket  124  connected through a chain  120  to the driving sprocket  116 , for transmitting the power to a front drive shaft  122 .  
         [0016]    The slide manipulation device includes a shift  126  connected to the sleeve  108 , a shift rail  127  for guiding the shift fork  126 , a shift cam for providing a moving force to the shift fork  126 , and an electric motor  130  for supplying an actuation power to the shift cam  128 .  
         [0017]    In the above described transfer, the power which has been supplied to the input shaft  100  is supplied through the sleeve  108  to the output shaft  102  in the AUTO mode, so that the driving power can be transmitted to the rear drive shaft. At the same time, the front drive shaft  122  receives the power from the output shaft  102  through the multi-plate clutch  112  and the chain  120 . Under this condition, the differences in revolution between the front wheels and the rear wheels are adjusted by the multi-plate clutch  112 .  
         [0018]    In the LOW mode, the sleeve  108  supplies the power of the input shaft  100  through the planetary carrier  106  to the output shaft  102 , so that a low velocity driving force or torque can be transmitted to the output shaft  102  compared with the AUTO mode. The strong driving force or torque thus created is transmitted through the multi-plate clutch  112  to the front drive shaft  122 .  
         [0019]    As shown in FIGS. 3 and 4, similar to the typical automatic transfer case, a sleeve  1  rotates together with an output shaft  102 , and is preferably coupled to the output shaft  102  with splines so that the sleeve  1  is capable of linear movement along the axial or longitudinal direction of the output shaft  102 . A rack  3  is formed parallel to the output shaft  102  by varying the shape of the portion where the conventional shift fork is connected. The rack  3  is preferably provided with a plurality of round teeth in one row, because the sleeve  1  is of a rotating cylindrical shape.  
         [0020]    A rotation torque supplying mechanism is connected to the rack  3  and meshed to it, and therefore, the sleeve  1  can be linearly moved on the output shaft  102 . The rotation torque supplying mechanism includes a driving gear  5  meshed through a plain gear to the rack  3 , and a motor  7  for providing power to the driving gear  5 . A clutch shifts the meshed status between the driving gear  5  and the rack  3 , whereby the sleeve  1  of the rack  3  is linearly moved by the rotational force of the motor  7 . The clutch ensures that the driving gear  5  and the rack  3  can be meshed together only during shifting. The meshed portion generates friction if the driving gear  5  and the rack  3  are to be maintained meshed together at other times. The clutch includes a rotation shaft set of the driving gear  5 , comprising a driving shaft  5 - 1  and a driven shaft  5 - 2 . The two shafts are spline-coupled in the axial direction. First and second electromagnets  9  and  11  selectively supply the magnetic forces to both sides of a flange  5 - 3  of the driven shaft  5 - 2 , so as to make the driving shaft  5 - 1  linearly move in the axial direction relative to the driven shaft  5 - 2 .  
         [0021]    The first electromagnet  9  is installed within the transfer housing beside the flange  5 - 3  near the sleeve  1 . The second electromagnet  11  is installed within the transfer housing near the motor  7 ; disposed so that it can pull the flange  5 - 3  by means of the electrically energized magnetic forces. Further, within the transfer housing to the side of the sleeve  1 , bearings  13  are disposed at a position where the flange  5 - 3  and the driven shaft  5 - 2  make contact.  
         [0022]    Shifting from an AUTO mode to a LOW mode and vice versa should be undertaken after the vehicle has come to a complete stop. In the case of a vehicle with a manual transmission, the mode shifting must be performed with the clutch pedal pressed down, while for an automatic transmission, the shift lever must first be placed into neutral (N) before mode shifting can be carried out.  
         [0023]    If the driver carries out the mode shifting when the vehicle is parked and the power is not supplied to the input shaft  100 , then the driving power of the motor  7  is transmitted through the driving gear  5  to the rack  3  of the sleeve  1 . Accordingly, the sleeve  1  moves longitudinally along the output shaft  102 , so that the direct connection between the input shaft  100  and the output shaft  102  is shifted from, or to, the connection of the input shaft  100  through the planetary carrier  106  to the output shaft  102 . That is, if the driver switches from an AUTO mode to a LOW mode or vice versa, the electric power is supplied to the first electromagnet  9 , and therefore, the driven shaft  5 - 2  of the driving gear moves left (in FIG. 4) toward the rack  3  due to the moving of the flange  5 - 3  toward the first electromagnet, so that the gear portion is meshed to the rack  3  of the sleeve. Then the motor  7  is activated to drive the driving gear  5 , and therefore, the sleeve  1  moves right (in FIG. 3), so that the input shaft  100  is connected through the planetary carrier  106  to the output shaft  102 .  
         [0024]    After the shifting actuation is completed, the power is supplied to the second electromagnet  11 , and therefore, the driven shaft  5 - 2  moves toward the motor  7 , so that the direct mesh between the driven shaft  5 - 2  and the rack  3  is released, thereby preventing friction between the rack  3  and the driving gear  5  while the vehicle is in motion.  
         [0025]    If the driver shifts from a LOW mode to an AUTO mode, then the electric power is supplied to the first electromagnet  9 . Consequently, the driven shaft  5 - 2  of the driving gear moves left (in FIG. 4) to mesh the driving gear  5  with the rack  3  of the sleeve. Then, since the motor  7  rotates in the reverse direction, the sleeve  1  moves leftward, so that the input shaft  100  and the output shaft  102  are directly meshed together. Thereafter, power is supplied to the second electromagnet  11 , and the driving gear  5  moves away from the rack  3  of the sleeve.  
         [0026]    The foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.