Abstract:
Disclosed is a range shift mechanism in the form of a floating planetary gear assembly for a transfer case. The range shift mechanical according to the present invention can improve power efficiency and generate low noises by suppressing gear rotation in a high range mode of the range shift system.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0156090 filed on Dec. 28, 2012, which is herein incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a transfer case for transferring a drive torque to a front axle in an all-wheel driving system for a rear wheel driving vehicle. More particularly, the present invention relates to a range shift mechanism in the form of a planetary gear assembly system shifting the speed between a high range and a low range in a transfer case. 
         [0004]    2. Description of the Related Art 
         [0005]    A transfer case is a device of a 4-wheel or all-wheel driving system for a rear wheel driving vehicle. The transfer case receives a driving force from a transmission and transfers the driving force to a front axle and a rear axle. The transfer case supports two types of range shift mechanisms, that is, a mode shift mechanism and a range shift mechanism. 
         [0006]      FIG. 1  is a schematic diagram illustrating a driveline of a general 4-wheel driving vehicle including a transfer case  100 . 
         [0007]    In a rear wheel driving vehicle, the driving force of an engine  1  is transferred to a rear wheel R through a transmission  2 , a rear wheel driving shaft  3  and a rear axle assembly  5 . In order to establish a 4-wheel or all-wheel system, the transfer case  100  is installed between the transmission  2  and the rear wheel driving shaft  3 . In addition, the transfer case  100  distributes the driving force to a front wheel F through the front axle assembly  4 . 
         [0008]    The transfer case  100  includes a mode shift mechanism  110  and a range shift mechanism  120 . The mode shift mechanism  110  of the transfer case  100  provides shifting between the 2-wheel driving mode and a 4-wheel driving mode, and the range shift mechanism  120  provides shifting between a high range mode and a low range mode. 
         [0009]    The high range mode is selected to ensure safe running by increasing a ground contact force through uniform power distribution of 25% for each of front and rear wheels to prevent slips or tire damages due to excessive power of 50% transferred to the rear wheels on an unpaved road or a road in a bad condition. During normally running, even when the road condition is bad due to snow or rain, highly efficient driving can be delivered. In the high range mode, the driving speed is constant relative to a transmission speed in a two-wheel drive mode (average gear ratio of 1:1). 
         [0010]    The low range mode is selected to ensure maximum traction force and high speed running. In the low range mode, high driving performance is demonstrated in running on the road of a steep slope or in pulling a vehicle. In particular, the low range mode allows excellent escape performance on an unpaved road in a severely adverse condition (a muddy road, a creviced road, a road with a side slope, a road with a steep slope, etc.). In the low range mode, the driving speed has a high reduction ratio relative to a transmission speed in a two-wheel drive mode (average gear ratio of around 1:2). 
         [0011]      FIG. 2  is a cross-sectional view of a general range shift mechanism  120  including the transfer case  100  shown in  FIG. 1 . 
         [0012]    The range shift mechanism  120  includes a planetary gear assembly system  130 , and the planetary gear assembly system  130  includes a sun gear  131 , a pinion gear  132 , a ring gear  133  and a carrier  135 . 
         [0013]    In the general range shift mechanism  120 , the ring gear  133  is fixed to the housing  121 , and the sun gear  131  and the pinion gear  132  rotate within the ring gear  133  that is fixed all the time for power transfer. Here, undefined reference numeral “ 141 ” denotes a sleeve connected to a shift lever. 
         [0014]    The mode shift mechanism allows a driver to shift the drive mode from a “2-wheel drive mode” to “4-wheel drive mode” while the range shift mechanism  120  allows shifting between a “high range mode” and a “low range mode”. 
         [0015]    The range shift mechanism  120  typically includes a planetary gear assembly system  130 . In the high range mode, the sun gear  131  is connected to an output shaft OP, and speed reduction occurs in the planetary gear assembly system  130 . The low range mode is employed only under a low-speed condition or a heavily loaded condition, for example, such a case of pulling of a heavy load or driving on an unpaved road. The percentage of using the low range mode is 1% or less. 
         [0016]    In the general range shift mechanism  120 , the ring gear  133  is fixed to the housing  121 , and continuous gear rotation occurs all the time between the sun gear  131 , the pinion gear  132  and the ring gear  133 . In the high range mode used by 99% or greater in the general range shift mechanism  120 , speed reduction by the planetary gear assembly system  130  is not required. In the high range mode in which the sun gear  131  is directly connected to the output shaft OP, the pinion gear  132  rotates between the sun gear  131  and the ring gear  133 . Such gear rotation causes a loss in the power and gear noises. 
       SUMMARY OF THE INVENTION 
       [0017]    In order to overcome the above-mentioned shortcomings, the present invention provides improvement of the power efficiency of a range shift mechanism by suppressing gear rotation in the high range mode, which is the most part of the use by the range shift mechanism and a solution to a problem with noise generation. 
         [0018]    According to an aspect of the invention, there is provided a range shift mechanism including an input shaft providing a driving force to a sun gear, an output shaft arranged coaxially with the input shaft and rotating independently of the input shaft, a sun gear having a clutch gear at its one side portion to be connected with a carrier and integrated with the input shaft, a carrier arranged coaxially with the sun gear, directly connected to the output shaft and having a clutch gear at its one side portion to be to be connected with the sun gear, a plurality of pinion gears radially installed on the carrier and meshed with the sun gear and a ring gear, a floating ring gear arranged coaxially with the output shaft, freely rotating on the output shaft in a coaxial direction and having a clutch gear at its one side portion to be connected with a housing, a sleeve having a clutch gear to be connected with the sun gear, the ring gear and a housing clutch gear, axially sliding on the input shaft by a fork and having a circumferential groove to be connected with the fork, and a fork and a guide rail axially moving the sleeve. 
         [0019]    The planetary gear assembly system may have a low range mode in which a gear ratio is 1.4:1 to 4.5:1. 
         [0020]    The floating ring gear may be capable of freely rotating axially on the output shaft, fixed to the input shaft and the output shaft in a high range mode and fixed to the housing in a low range mode. 
         [0021]    The sleeve may control connections between each of the sun gear, the ring gear and the housing, in the high range mode, the clutch gear installed on the sleeve may connect the clutch gear installed on the sun gear and the clutch gear installed on the carrier, the planetary gear assembly system, including the sun gear, the pinion gears, the pinion shaft and the ring gear, may be integrated into one single unit and rotate together, and in the low range mode, the clutch gear installed on the sleeve connects the housing clutch gear and the clutch gear installed on the ring gear, and ring gear rotation may not occur in a fixed state. 
         [0022]    The carrier may be connected to the output shaft and may include a clutch carrier on its one side portion to enable smooth connection with the sun gear by the sleeve. 
         [0023]    The sun gear may include a clutch gear on its one side portion to enable smooth connection with the carrier by the sleeve. 
         [0024]    The housing clutch gear may be fixed to the housing to enable smooth connection with the ring gear by the sleeve in the low range mode. 
         [0025]    Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The above and other features and advantages will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings, in which: 
           [0027]      FIG. 1  is a schematic diagram illustrating a driveline of a general 4-wheel driving vehicle including a transfer case; 
           [0028]      FIG. 2  is a cross-sectional view of a general range shift mechanism including the transfer case shown in  FIG. 1 ; 
           [0029]      FIG. 3  illustrates an exemplary embodiment of a floating planetary range shift mechanism according to the present invention; 
           [0030]      FIGS. 4A ,  4 B and  4 C are detailed diagrams of a portion “A” of  FIG. 3 , specifically illustrating a relationship between a sleeve and a carrier in a high range mode in  FIG. 4A , a position of a sleeve in a low range mode in  FIG. 4B , and a position of a sleeve in a neutral range mode; 
           [0031]      FIG. 5  illustrates the power transfer path in the high range mode according to the present invention shown in  FIG. 4A ; and 
           [0032]      FIG. 6  illustrates the power transfer path in the low range mode according to the present invention shown in  FIG. 4B . 
       
    
    
       [0033]    In the following description, the same or similar elements are labeled with the same or similar reference numbers. 
       DETAILED DESCRIPTION 
       [0034]    The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
         [0035]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0036]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
         [0037]    Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings in such a manner that the technical idea of the present disclosure may easily be carried out by a person with ordinary skill in the art to which the invention pertains. Objects, operations, effects, other objects, characteristics and advantages of the present disclosure will be easily understood from an explanation of a preferred embodiment that will be described in detail below by reference to the attached drawings. 
         [0038]    Although embodiments have been described with reference to illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. 
         [0039]      FIG. 3  illustrates an exemplary embodiment of a floating planetary range shift mechanism according to the present invention. 
         [0040]    The range shift mechanism  200  according to the embodiment of the present invention includes a planetary gear assembly system  210 . The planetary gear assembly system  210  includes a sun gear  211 , a pinion gear  212 , a ring gear  213  and a carrier  215 . In particular, the planetary gear assembly system  210  further includes a first clutch C- 1  installed in the ring gear  213 . Here, undefined reference numeral “ 212 - 1 ” denotes a pinion gear shaft, and the pinion gear  212  is rotatably fixed to the carrier  215  through the pinion gear shaft  212 - 1 . 
         [0041]    The planetary gear assembly system  210  performs a function of shifting a speed ratio between an input shaft IP and an output shaft OP. The input shaft IP is directly connected to the sun gear  211  of the planetary gear assembly system  210 , and the output shaft OP is connected to the carrier  35 . 
         [0042]    The ring gear  213  is of a floating type and may rotate with the input shaft IP and the output shaft OP. As compared with the general range shift mechanism  120  shown in  FIG. 2 , the most significant characteristic of the present invention is the structure of the ring gear  213 . 
         [0043]    The first clutch gear C- 1  installed in the ring gear  213  is connected to the ring gear  213 , and a second clutch gear C- 2  is installed in the housing  201 . Meanwhile, a third clutch gear C- 3  is installed on the input shaft IP, and a fourth clutch gear C- 4  is installed on the carrier  215 . 
         [0044]    In addition, a sleeve  230  is installed on a circumferential portion of the input shaft IP. The sleeve  230  slides on the input shaft IP and controls connections between each of the input shaft IP, the planetary gear assembly system  230  and the housing  210 . 
         [0045]    If the sleeve  230  moves on the input shaft IP to the right (of the drawing) in a high range mode by a fork  231  connected to a shift lever (not shown), the third clutch gear C- 3  on the input shaft IP is connected to the fourth clutch gear C- 4  on the carrier  215 . Since the carrier  215  is directly connected to the output shaft OP, the input shaft IP is directly connected to the output shaft OP, with a gear ratio of 1:1. 
         [0046]    Under these conditions, the planetary gear assembly system  210  including the ring gear  213  is one single unit and rotates together with shafts (IP and OP shafts). That is to say, there is no rotation of a gear meshed with another gear, leading to no loss in the power due to gear rotation. In addition, noises due to gear rotation are not generated, and supply of a lubricating oil is not coercively required. 
         [0047]    The power transfer path, as indicated by the arrow, in the high range mode according to the present invention shown in  FIG. 4A  is illustrated in  FIG. 5 . 
         [0048]    As compared with the general range shift mechanism  120  shown in  FIG. 2 , the range shift mechanism  200  according to the present invention is highly efficient and generates a small amount of noises in the high range mode used by 99% or greater for the most part of operating time. 
         [0049]    Meanwhile, in the low range mode shown in  FIG. 4B , if a driver moves the sleeve  230  using the fork  231  to the left (of the drawing), the first clutch gear C- 1  on the ring gear  213  is connected to the second clutch gear C- 2  mounted on the housing  201 . Since the ring gear  213  is fixed to the housing  201 , it does not move. In addition, since the input shaft IP is connected to the sun gear  211 , it does not move, either. 
         [0050]    The input shaft IP is connected to the sun gear  211 , which is connected to the carrier  215 . Since the ring gear  213  is fixed to the housing  201 , a slight speed reduction occurs between the input shaft IP and the output shaft IP. 
         [0051]    The power transfer path, as indicated by the arrow, in the low range mode according to the present invention shown in  FIG. 4B  is illustrated in  FIG. 6 . 
         [0052]    As described above, according to the present invention, in the high range mode, the planetary gear assembly system rotates with a shaft without gear rotation between the sun gear, the planetary gear assembly system and the ring gear. However, in the low range mode, the ring gear is fixed to a housing, and gear rotation occurs in the planetary gear assembly system. Since the low range mode infrequently occurs, the range shift mechanism maintains high efficiency and low noise conditions for the most part of operating time. In addition, since there is no gear rotation in the low range mode, a gear lubricating oil is required only in the low range mode. The power consumed by the lubricating oil of a general oil pump can be reduced. Therefore, the present invention is advantageous in view of high fuel efficiency and low noise. 
         [0053]    Although the range shift system for transfer case according to an exemplary embodiment of the present invention has been described in detail hereinabove, it should be understood that many variations and modifications of the basic inventive concept herein described, which may appear to those skilled in the art, will still fall within the spirit and scope of the exemplary embodiments of the present invention as defined by the appended claims. 
         [0054]    The drawings and the forgoing description gave examples of the present invention. The scope of the present invention, however, is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of the invention is at least as broad as given by the following claims.