Patent Publication Number: US-2022234662-A1

Title: Vehicle for uneven terrain

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a bypass continuation of PCT Application No. PCT/KR2021/017760, filed on Nov. 29, 2021, which claims priority to Korean Patent Application No. 10-2020-0167813, filed on Dec. 3, 2020, and Korean Patent Application No. 10-2021-0026677, filed on Feb. 26, 2021, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     1. Field 
     The disclosure relates to a vehicle capable of moving on various terrain, and more particularly, to a vehicle for uneven terrain in which a relative height of wheels is adjusted depending on a curvature of the terrain, and a wheelbase can be actively adjusted depending on the size of an obstacle. 
     2. Description of Related Art 
     Related art vehicles using wheels may transport goods using minimal power. 
     However, the related art vehicle using wheels may easily move on flat ground, but has a problem in that it is difficult to move up/down stairs. 
     In order to solve the problem, various vehicles have been developed. 
     For example, U.S. Patent Application Publication No. 2017/0015168 discloses a vehicle capable of climbing the stairs. 
     The vehicle according to the related art described above has at least four wheels, and has a structure in which two wheels are rotatably hinged to the base in pairs. Two pairs of wheels may rotate relative to the pivot point so that the vehicle can climb stairs. 
     However, the vehicle according to the related art has a problem in that it is impossible to climb the stairs in a direction perpendicular to the stairs when the distance between the wheels coincides with the step width of the stairs or the sum of a plurality of step widths. 
     In addition, because the side wheels are structured to generate forward and backward movements in opposite directions when moving up and down, when moving on uneven terrain, they do not go straight and inevitably cause yaw rotation or rolling rotation. 
     SUMMARY 
     Provided are a vehicle for uneven terrain in which each wheel can move up and down, and a wheelbase between a front wheel and a rear wheel can be varied so as to climb obstacles of various sizes including stairs. 
     According to an aspect of the disclosure, there is provided a vehicle including: a main frame; a front wheel assembly disposed in front of the main frame and including a front wheel; a rear wheel assembly disposed behind the main frame and including a rear wheel; a wheelbase adjuster disposed between the front wheel assembly and the rear wheel assembly and configured to adjust a wheelbase between the front wheel and the rear wheel; a first side wheel assembly pivotably disposed on one side of the main frame and including a first side wheel; a second side wheel assembly pivotably disposed on another side of the main frame and including a second side wheel that is opposite to the first side wheel; a front wheel torque transmitter configured to interlock a vertical movement of the front wheel and a vertical movement of the first side wheel; a rear wheel torque transmitter configured to interlock a vertical movement of the rear wheel and a vertical movement of the second side wheel; and a stabilizer disposed in the main frame and configured to support the first side wheel assembly and the second side wheel assembly so that the first side wheel and the second side wheel are positioned at a same height. 
     The wheelbase adjuster may include: a front wheel moving part configured to linearly move the front wheel assembly; and a rear wheel moving part disposed in parallel to the front wheel moving part and configured to linearly move the rear wheel assembly. 
     Each of the front wheel moving part and the rear wheel moving part may include a linear motion guide. 
     The front wheel moving part may include a front wheel rack disposed under the linear motion guide of the front wheel moving part, the rear wheel moving part may include a rear wheel rack disposed in parallel and opposite to the front wheel rack, and at least one pinion may be disposed between the front wheel rack and the rear wheel rack. 
     The front wheel torque transmitter may include: a spline shaft disposed parallel to and above the linear motion guide of the front wheel moving part; a first front wheel bevel gear disposed at a leading end of the spline shaft; and a second front wheel bevel gear disposed at a rear end of the front wheel assembly and meshed with the first front wheel bevel gear. 
     The front wheel assembly may be pivotably disposed at a front end of the front wheel moving part, the second front wheel bevel gear may be configured to rotate integrally with the front wheel assembly, and the front wheel may be rotatably disposed at a front end of the front wheel assembly. 
     The vehicle may further include a front shock absorber disposed between the front wheel moving part and the front wheel assembly. 
     The rear wheel torque transmitting device may include: a spline shaft disposed parallel to and above the linear motion guide of the rear wheel moving part; a first rear wheel bevel gear disposed at a leading end of the spline shaft; and a second rear wheel bevel gear disposed at a front end of the rear wheel assembly and meshed with the first rear wheel bevel gear. 
     The rear wheel assembly may be pivotably disposed at a rear end of the rear wheel moving part, the second rear wheel bevel gear may be configured to rotate integrally with the rear wheel assembly, and the rear wheel may be rotatably disposed at a rear end of the rear wheel assembly. 
     The vehicle may further include a rear shock absorber disposed between the rear wheel moving part and the rear wheel assembly. 
     The front wheel moving part may include a first linear motion guide that may include a block and a rail, the rear wheel moving part may include a second linear motion guide that may include a block and a rail, the block of the first linear motion guide and the block of the second linear motion guide may be disposed on the main frame, and the front wheel assembly may be pivotably disposed at one end of the rail of the first linear motion guide, and the rear wheel assembly is pivotably disposed at one end of the rail of the second linear motion guide. 
     The wheelbase adjuster may further include a locking device configured to lock the front wheel moving part and the rear wheel moving part such that a size of the wheelbase becomes fixed. 
     The front wheel moving part may include a front wheel rack, the rear wheel moving part may include a rear wheel rack disposed parallel and opposite to the front wheel rack, at least one pinion disposed between the front wheel rack and the rear wheel rack, and the locking device may be configured to selectively lock the at least one pinion. 
     The locking device may include: a lifting stopper configured to selectively lock the at least one pinion; and an actuator configured to move the lifting stopper up and down. 
     The at least one pinion may include a plurality of coupling grooves provided on an upper surface thereof, the lifting stopper may include: a moving plate configured to be moved up and down by the actuator and including a plurality of coupling protrusions that are configured to engage with the plurality of coupling grooves; a fixed plate disposed above the moving plate and spaced apart from the moving plate by a predetermined distance; and a plurality of elastic members provided between the moving plate and the fixed plate, and based on the moving plate being lowered by the actuator and the plurality of coupling protrusions being engaged with the plurality of coupling grooves of the at least one pinion, the at least one pinion may be locked so as to not rotate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view illustrating a vehicle for uneven terrain according to an embodiment; 
         FIG. 2  is a partial plan view of the vehicle for uneven terrain of  FIG. 1 ; 
         FIG. 3  is a perspective view illustrating a vehicle for uneven terrain according to an embodiment; 
         FIG. 4  is a partial plan view of the vehicle for uneven terrain of  FIG. 3 ; 
         FIG. 5  is a cross-sectional view illustrating the vehicle for uneven terrain of  FIG. 3  taken along line I-I; 
         FIG. 6  is a cross-sectional view illustrating the vehicle for uneven terrain of  FIG. 3  taken along line II-II; 
         FIG. 7  is a plan view illustrating a state in which a main frame is removed from the vehicle for uneven terrain of  FIG. 3 ; 
         FIG. 8  is a partial perspective view illustrating a front wheel frame of a vehicle for uneven terrain according to an embodiment; 
         FIG. 9  is a partial perspective view illustrating a rear wheel frame of a vehicle for uneven terrain according to an embodiment; 
         FIG. 10  is a perspective view illustrating a locking device of a vehicle for uneven terrain according to an embodiment; 
         FIG. 11  is a partial view illustrating racks and pinions of a locking device of a vehicle for uneven terrain according to an embodiment; 
         FIG. 12A  is a view illustrating a state in which a pinion of a locking device of a vehicle for uneven terrain according to an embodiment is locked and is unable to rotate; 
         FIG. 12B  is a view illustrating a state in which a pinion of a locking device of a vehicle for uneven terrain according to an embodiment is released and is able to rotate; 
         FIG. 13  is a perspective view illustrating a state in which a wheelbase of a vehicle for uneven terrain according to an embodiment is maximized; 
         FIG. 14  is a plan view of the vehicle for uneven terrain of  FIG. 13 ; 
         FIG. 15  is a partial cross-sectional view illustrating the vehicle for uneven terrain of  FIG. 13  taken along line III-III; 
         FIG. 16  is a plan view illustrating a state in which a main frame is removed from the vehicle for uneven terrain of  FIG. 13 ; and 
         FIG. 17  is a block diagram illustrating a vehicle for uneven terrain according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the disclosure will hereinafter be described with reference to the accompanying drawings. However, it is to be understood that embodiments of the present disclosure are not limited to the described example embodiments, and include various modifications, equivalents, and/or alternatives according to embodiments of the disclosure. The matters defined herein, such as a detailed construction and elements thereof, are provided to assist in a comprehensive understanding of the present disclosure. Thus, it is apparent that example embodiments may be carried out without those defined matters. Also, well-known functions or constructions are omitted to provide a clear and concise description of example embodiments. Further, dimensions of various elements in the accompanying drawings may be arbitrarily increased or decreased for assisting in a comprehensive understanding. 
     The terms ‘first’, ‘second’, etc. may be used to describe diverse components, but the components are not limited by the terms. The terms may only be used to distinguish one component from the others. For example, without departing from the scope of the present disclosure, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component. 
     The terms used in embodiments of the present disclosure may be construed as commonly known to those skilled in the art unless otherwise defined. 
     Further, the terms ‘leading end’, ‘rear end’, ‘upper side’, ‘lower side’, ‘top end’, ‘bottom end’, etc. used in the present disclosure are defined with reference to the drawings. However, the shape and position of each component are not limited by the terms. 
     Hereinafter, non-limiting example embodiments of a vehicle for uneven terrain according to the disclosure will be described with reference to the accompanying drawings. 
       FIG. 1  is a perspective view illustrating a vehicle for uneven terrain according to an embodiment, and  FIG. 2  is a partial plan view of the vehicle for uneven terrain of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , a vehicle  1  for uneven terrain according to an embodiment may include a main frame  10 , a first side wheel assembly  22 , a second side wheel assembly  32 , a front wheel moving part  50 , a front wheel assembly  60 , a rear wheel moving part  80 , and a rear wheel assembly  90 . 
     The first side wheel assembly  22  may be disposed on one side of the main frame  10 . A first side wheel  21  may be disposed on one end of the first side wheel assembly  22 . The first side wheel  21  may be rotatably disposed under the first side wheel assembly  22 . 
     The second side wheel assembly  32  may be disposed to face the first side wheel assembly  22  on the other side of the main frame  10 . A second side wheel  31  may be disposed at one end of the second side wheel assembly  32 . The second side wheel  31  may be rotatably disposed under the second side wheel assembly  32 . 
     Each of the first side wheel  21  and the second side wheel  31  may be configured as a motorized wheel in which a driving motor is built-in. 
     The front wheel moving part  50  is disposed on the main frame  10  and may be formed to linearly move the front wheel assembly  60 . 
     The front wheel assembly  60  is disposed in front of the main frame  10 , and may be provided to linearly move back and forth with respect to the main frame  10 . In addition, the front wheel assembly  60  may be provided to pivot at a predetermined angle with respect to the main frame  10 . 
     A front wheel  41  may be rotatably disposed at the front end of the front wheel assembly  60 . The front wheel  41  may be configured as a motorized wheel in which a driving motor is built-in. 
     The front wheel assembly  60  may be pivotably disposed at the front end of the front wheel moving part  50  provided to move linearly with respect to the main frame  10 . The front wheel  41  may be rotatably disposed under the front wheel assembly  60 . 
     The front wheel moving part  50  and the front wheel assembly  60  may be connected by a pair of bevel gears (e.g., a first front wheel bevel gear  56  and a second front wheel bevel gear  66 ). 
     The front wheel moving part  50  may include a spline shaft  51 . A first front wheel bevel gear  56  may be provided at the leading end of the spline shaft  51 . The first side wheel assembly  22  may be pivotably connected to the spline shaft  51  of the front wheel moving part  50 . 
     The front wheel assembly  60  may be provided with a second front wheel bevel gear  66  meshed with the first front wheel bevel gear  56 . The spline shaft  51 , the first front wheel bevel gear  56 , and the second front wheel bevel gear  66  may form a front wheel torque transmitting device  40  (e.g., a front wheel torque transmitter). Accordingly, the vertical movement of the front wheel  41  and the vertical movement of the first side wheel  21  may be interlocked with each other by the front wheel torque transmitting device  40 . 
     The rear wheel moving part  80  is disposed at the main frame  10 , and may be formed to linearly move the rear wheel assembly  90 . The front wheel moving part  50  and the rear wheel moving part  80  may form a wheelbase adjuster capable of adjusting the wheelbase between the front wheel  41  and a rear wheel  71 . 
     The rear wheel assembly  90  is disposed at the rear end of the main frame  10 , and may be provided to linearly move back and forth with respect to the main frame  10 . In addition, the rear wheel assembly  90  may be provided to pivot at a predetermined angle with respect to the main frame  10 . 
     The rear wheel  71  may be rotatably disposed at the rear end of the rear wheel assembly  90 . The rear wheel  71  may be configured as a motorized wheel having a built-in driving motor. 
     The rear wheel assembly  90  may be pivotably disposed at the rear end of the rear wheel moving part  80  provided to move linearly with respect to the main frame  10 . The rear wheel  71  may be rotatably disposed under the rear wheel assembly  90 . 
     The rear wheel moving part  80  and the rear wheel assembly  90  may be connected by a pair of bevel gears (e.g., a first rear wheel bevel gear  86  and a second rear wheel bevel gear  96 ). 
     The rear wheel moving part  80  may include a spline shaft  81 . A first rear wheel bevel gear  86  may be provided at the leading end of the spline shaft  81 . The second side wheel assembly  32  may be pivotably connected to the spline shaft  81  of the rear wheel moving part  80 . 
     The rear wheel assembly  90  may be provided with a second rear wheel bevel gear  96  meshed with the first rear wheel bevel gear  86 . The spline shaft  81 , the first rear wheel bevel gear  86 , and the second rear wheel bevel gear  96  may form a rear wheel torque transmitting device  70  (e.g., a rear wheel torque transmitter). Accordingly, the vertical movement of the rear wheel  71  and the vertical movement of the second side wheel  31  may be interlocked with each other by the rear wheel torque transmitting device  70 . 
     A locking device  100  is disposed at the main frame  10 , and may be provided to selectively lock the front wheel moving part  50  and the rear wheel moving part  80  with respect to the main frame  10 . When the locking device  100  operates to lock the front wheel moving part  50  and the rear wheel moving part  80 , the front wheel assembly  60  and the rear wheel assembly  90  may not move linearly back and forth with respect to the main frame  10 . Accordingly, the wheelbase between the front wheel  41  and the rear wheel  71  does not change. 
     When the locking device  100  is released, the front wheel moving part  50  and the rear wheel moving part  80  may linearly move back and forth with respect to the main frame  10 . Accordingly, the wheelbase between the front wheel  41  and the rear wheel  71  changes according to the moving direction of each of the front wheel  41  and the rear wheel  71 . 
     In detail, when the front wheel  41  rotates in one direction and moves forward, and the rear wheel  71  rotates in the opposite direction to the front wheel  41  and moves backward, the wheelbase between the front wheel  41  and the rear wheel  71  increases. Conversely, when the front wheel  41  rotates in the opposite direction and moves backward, and the rear wheel  71  rotates in the opposite direction to the front wheel  41  and moves forward, the wheelbase is reduced. 
     The vehicle  1  for uneven terrain according to an embodiment having the above-described structure may climb various obstacles because the wheelbase between the front wheel  41  and the rear wheel  71  may be adjusted according to the size of the obstacle. For example, when the obstacle is the stairs, the vehicle  1  for uneven terrain according to an embodiment may adjust the wheelbase between the front wheel  41  and the rear wheel  71  according to the edge interval of the stairs, thereby easily climbing stairs of various sizes. 
     Hereinafter, a vehicle  1  for uneven terrain according to an embodiment will be described in detail with reference to  FIGS. 3 to 9 . 
       FIG. 3  is a perspective view illustrating a vehicle for uneven terrain according to an embodiment, and  FIG. 4  is a plan view of the vehicle for uneven terrain of  FIG. 3 .  FIG. 5  is a cross-sectional view illustrating the vehicle for uneven terrain of  FIG. 3  taken along line I-I.  FIG. 6  is a cross-sectional view illustrating the vehicle for uneven terrain of  FIG. 3  taken along line II-II.  FIG. 7  is a plan view illustrating a state in which a main frame is removed from the vehicle for uneven terrain of  FIG. 3 .  FIG. 8  is a partial perspective view illustrating a front wheel frame of a vehicle for uneven terrain according to an embodiment.  FIG. 9  is a partial perspective view illustrating a rear wheel frame of a vehicle for uneven terrain according to an embodiment. 
     Referring to  FIGS. 3 to 7 , a vehicle  1  for uneven terrain according to an embodiment may include a main frame  10 , a first side wheel assembly  22 , a second side wheel assembly  32 , a front wheel assembly  60 , a rear wheel assembly  90 , a wheelbase adjuster  20 , a front wheel torque transmitting device  40 , and a rear wheel torque transmitting device  70 . 
     The main frame  10  may be formed to support the wheelbase adjuster  20 , the first side wheel assembly  22 , and the second side wheel assembly  32 . A plurality of storage containers  11  may be provided in the main frame  10 . A power source such as a battery, a processor configured to control the vehicle  1  for uneven terrain, and the like may be disposed inside the storage containers  11 . 
     A lower frame  12  may be provided under the main frame  10 . The lower frame  12  may be spaced apart from the main frame  10  by a predetermined distance. A locking device  100  may be disposed in the lower frame  12 . 
     The first side wheel assembly  22  may be provided to rotatably support the first side wheel  21 . The first side wheel assembly  22  may be disposed on one side, for example, the right side of the main frame  10 . The first side wheel assembly  22  may be provided to pivot at a predetermined angle with respect to the main frame  10 . 
     A first side wheel support frame  23  may be disposed at one end of the first side wheel assembly  22 . The first side wheel  21  may be rotatably disposed under the first side wheel support frame  23 . 
     The first side wheel assembly  22  may be formed as a double frame. In other words, the first side wheel assembly  22  may include a first upper frame  22   a  and a first lower frame  22   b  spaced downward from the first upper frame  22   a  by a predetermined distance. 
     One end of the first upper frame  22   a  may be pivotably connected to the front wheel moving part  50  of the wheelbase adjuster  20  to be described later. The other end of the first upper frame  22   a  may be pivotably connected to the first side wheel support frame  23 . 
     One end of the first lower frame  22   b  may be pivotably connected to the lower frame  12 . The other end of the first lower frame  22   b  may be pivotably connected to the first side wheel support frame  23 . Accordingly, the first upper frame  22   a , the first lower frame  22   b , the first side wheel support frame  23 , and the lower frame  12  may form a four-bar linkage. 
     The second side wheel assembly  32  may be provided to rotatably support the second side wheel  31 . The second side wheel assembly  32  may be disposed on the other side of the main frame  10  opposite to the first side wheel assembly  22 , for example, on the left side of the main frame  10 , and may be provided to pivot at a predetermined angle with respect to the main frame  10 . 
     A second side wheel support frame  33  may be disposed at one end of the second side wheel assembly  32 . The second side wheel  31  may be rotatably disposed under the second side wheel support frame  33 . The rotation shaft of the second side wheel  31  may be disposed to be positioned in a straight line with the rotation shaft of the first side wheel  21  of the first side wheel assembly  22 . 
     The second side wheel assembly  32  may be formed as a double frame. In other words, the second side wheel assembly  32  may include a second upper frame  32   a  and a second lower frame  32   b  spaced downward from the second upper frame  32   a  by a predetermined distance. 
     One end of the second upper frame  32   a  may be pivotably connected to the rear wheel moving part  80  of the wheelbase adjuster  20  to be described later. The other end of the second upper frame  32   a  may be pivotably connected to the second side wheel support frame  33 . 
     One end of the second lower frame  32   b  may be pivotably connected to the lower frame  12 . The other end of the second lower frame  32   b  may be pivotably connected to the second side wheel support frame  33 . Accordingly, the second upper frame  32   a , the second lower frame  32   b , the second side wheel support frame  33 , and the lower frame  12  may form a four-bar linkage. 
     The first side wheel assembly  22  and the second side wheel assembly  32  may be supported with a stabilizer  30  relative to the main frame  10 . Accordingly, the suspension of the first side wheel  21  and the suspension of the second side wheel  31  may be interlocked by the stabilizer  30 . 
     The stabilizer  30  may include a first two-bar linkage  25  supporting the first side wheel assembly  22 , a second two-bar linkage  35  supporting the second side wheel assembly  32 , and a stabilizer bar  30   a  connecting the first two-bar linkage  25  and the second two-bar linkage  35 . 
     The stabilizer bar  30   a  may be rotatably disposed on the main frame  10 . For example, both ends of the stabilizer bar  30   a  may be disposed to be supported by bearings  15  provided at the main frame  10 . 
     One end of the stabilizer bar  30   a  may be connected to the first two-bar linkage  25 . 
     The first two-bar linkage  25  may include a first horizontal linkage  25   a  and a first vertical linkage  25   b . One end of the first vertical linkage  25   b  may be connected to the first lower frame  22   b , and the other end of the first vertical linkage  25   b  may be connected to one end of the first horizontal linkage  25   a . The other end of the first horizontal linkage  25   a  may be connected to one end of the stabilizer bar  30   a.    
     The other end of the stabilizer bar  30   a  may be connected to the second two-bar linkage  35 . 
     The second two-bar linkage  35  may include a second vertical linkage  35   a  and a second horizontal linkage  35   b . One end of the second vertical linkage  35   a  may be connected to the second lower frame  32   b , and the other end of the second vertical linkage  25   a  may be connected to one end of the second horizontal linkage  35   b . The other end of the second horizontal linkage  35   b  may be connected to the other end of the stabilizer bar  30   a.    
     Accordingly, the movement of each of the first two-bar linkage  25  and the second two-bar linkage  35  may be transmitted to the opposite side through the stabilizer bar  30   a . In other words, because the movement of the first side wheel assembly  22  in which the first side wheel  21  is disposed is transmitted to the second two-bar linkage  35  through the first two-bar linkage  25  and the stabilizer bar  30   a , the second side wheel assembly  32  in which the second side wheel  31  is disposed may be moved interlocking with the first side wheel assembly  22 . 
     For example, when the first side wheel  21  of the first side wheel assembly  22  moves down, the second side wheel  31  of the second side wheel assembly  32  also moves down by the stabilizer  30 . 
     Conversely, because the movement of the second side wheel assembly  32  in which the second side wheel  31  is disposed may be transmitted to the first two-bar linkage  25  through the second two-bar linkage  35  and the stabilizer bar  30   a , the first side wheel assembly  22  may be moved interlocking with the second side wheel assembly  32 . 
     For example, when the second side wheel  31  of the second side wheel assembly  32  moves down, the first side wheel  21  of the first side wheel assembly  22  also moves down by the stabilizer  30 . Accordingly, the first side wheel  21  and the second side wheel  31  may be positioned at approximately the same height by the stabilizer  30 . 
     The first side wheel  21  and the second side wheel  31  may be configured as motorized wheels in which a first side wheel driving motor  24  and a second side wheel driving motor  34  are built-in, respectively. The first side driving motor  24  is fixed to the first side wheel support frame  23 , and the second side driving motor  34  is fixed to the second side wheel support frame  33 . Accordingly, the first side wheel  21  and the second side wheel  31  may rotate with respect to the first side wheel support frame  23  and the second side wheel support frame  33 , respectively. 
     As another example, each of the first side wheel  21  and the second side wheel  31  may be configured to receive power from an externally disposed driving motor through a power transmission device such as pulleys and a belt, or the like. 
     The front wheel assembly  60  is disposed in front of the main frame  10 , and may be provided to be linearly moved back and forth with respect to the main frame  10 . Also, the front wheel assembly  60  may be provided to pivot at a predetermined angle with respect to the main frame  10 . 
     The front wheel  41  may be rotatably disposed at the front end of the front wheel assembly  60 . The front wheel  41  may be configured as a motorized wheel in which a driving motor  42  is built-in. 
     The front wheel assembly  60  may be pivotably disposed at the front end of the front wheel moving part  50  provided to move linearly with respect to the main frame  10 . 
     Referring to  FIG. 8 , the front wheel assembly  60  is disposed in front of the front wheel moving part  50 , and is provided to pivot at a predetermined angle with respect to the front wheel moving part  50 . A front wheel support frame  43  supporting rotation of the front wheel  41  may be disposed at the front end of the front wheel assembly  60 . 
     The front wheel assembly  60  may be formed as a double frame. In other words, the front wheel assembly  60  may include an upper front frame  60   a  and a lower front frame  60   b  spaced downward by a predetermined distance from the upper front frame  60   a.    
     The rear end of the upper front frame  60   a  may be pivotably connected to a front plate  54  of the front wheel moving part  50 . A fixed shaft  54   a  may be provided at the upper end of the front plate  54  of the front wheel moving part  50 . The rear end of the upper front frame  60   a  may be rotatably connected to the fixed shaft  54   a  of the front plate  54 . The front end of the upper front frame  60   a  may be pivotably connected to the front wheel support frame  43 . 
     The rear end of the lower front frame  60   b  may be pivotably connected to the lower end of the front plate  54 . Accordingly, the front wheel assembly  60  may pivot at a predetermined angle with respect to the front plate  54  of the front wheel moving part  50 . The front end of the lower front frame  60   b  may be pivotably connected to the front wheel support frame  43 . 
     Accordingly, the upper front frame  60   a  and the lower front frame  60   b  of the front wheel assembly  60 , the front plate  54  of the front wheel moving part  50 , and the front wheel support frame  43  may form a four-bar linkage. 
     The front wheel support frame  43  may be formed to rotatably support the front wheel  41 . In addition, the front wheel support frame  43  may include a front wheel steering motor  46  for control the moving direction of the front wheel  41 . 
     For example, the front wheel support frame  43  may include a motor fixing part  44  formed to fix the front wheel steering motor  46 , and a front wheel support part  45  that is rotated by the front wheel steering motor  46  and supports the driving motor  42  of the front wheel  41 . Accordingly, when the front wheel steering motor  46  operates, the front wheel support part  45  rotates to change a moving direction of the front wheel  41 . When the driving motor  42  of the front wheel  41  operates, the front wheel  41  rotates so that the front wheel assembly  60  moves. 
     The rear wheel assembly  90  is disposed at the rear of the main frame  10 , and may be provided to move linearly back and forth with respect to the main frame  10 . In addition, the rear wheel assembly  90  may be provided to pivot at a predetermined angle with respect to the main frame  10 . 
     The rear wheel  71  may be rotatably disposed at the rear end of the rear wheel assembly  90 . The rear wheel  71  may be configured as a motorized wheel in which a driving motor  72  is built-in. 
     The rear wheel assembly  90  may be pivotably disposed at the front end of the rear wheel moving part  80  provided to move linearly with respect to the main frame  10 . The rear wheel  71  may be rotatably disposed at the rear end of the rear wheel assembly  90 . 
     Referring to  FIG. 9 , the rear wheel assembly  90  is disposed at the rear of the rear wheel moving part  80 , and may be provided to pivot at a predetermined angle with respect to the rear wheel moving part  80 . A rear wheel support frame  73  formed to rotatably support the rear wheel  71  may be disposed at the rear end of the rear wheel assembly  90 . 
     The rear wheel assembly  90  may be formed as a double frame. In other words, the rear wheel assembly  90  may include an upper rear frame  90   a  and a lower rear frame  90   b  spaced downward by a predetermined distance from the upper rear frame  90   a.    
     The front end of the upper rear frame  90   a  may be pivotably connected to a rear plate  84  of the rear wheel moving part  80 . A fixed shaft  84   a  may be provided at the upper end of the rear plate  84  of the rear wheel moving part  80 . The front end of the upper rear frame  90   a  may be rotatably connected to the fixed shaft  84   a  of the rear plate  84 . The rear end of the upper rear frame  90   a  may be pivotably connected to the rear wheel support frame  73 . 
     The front end of the lower rear frame  90   b  may be pivotably connected to the lower end of the rear plate  84 . Accordingly, the rear wheel assembly  90  may pivot at a predetermined angle with respect to the rear plate  84  of the rear wheel moving part  80 . The rear end of the lower rear frame  90   b  may be pivotably connected to the rear wheel support frame  73 . 
     Accordingly, the upper rear frame  90   a  and the lower rear frame  90   b  of the rear wheel assembly  90 , the rear plate  84  of the rear wheel moving part  80 , and the rear wheel support frame  73  may form a four-bar linkage. 
     The rear wheel support frame  73  may be formed to rotatably support the rear wheel  71 . In addition, the rear wheel support frame  73  may include a rear wheel steering motor  76  for changing the moving direction of the rear wheel  71 . 
     For example, the rear wheel support frame  73  may include a motor fixing part  74  formed to fix the rear wheel steering motor  76 , and a rear wheel support part  75  that is rotated by the rear wheel steering motor  76  and supports the driving motor  72  of the rear wheel  71 . Accordingly, when the rear wheel steering motor  76  operates, the rear wheel support part  75  rotates to change the moving direction of the rear wheel  71 . When the driving motor  72  of the rear wheel  71  operates, the rear wheel  71  rotates so that the rear wheel assembly  90  moves. 
     The wheelbase adjuster  20  may be formed to adjust the wheelbase between the front wheel  41  and the rear wheel  71 . The wheelbase adjuster  20  may be disposed in the main frame  10  between the front wheel assembly  60  and the rear wheel assembly  90 . 
     The wheelbase adjuster  20  may include the front wheel moving part  50  configured to linearly move the front wheel assembly  60  and the rear wheel moving part  80  configured to linearly move the rear wheel assembly  90 . The front wheel moving part  50  and the rear wheel moving part  80  may be disposed to face each other and to be parallel to each other. 
     The front wheel moving part  50  may be formed to linearly move back and forth with respect to the main frame  10 . Because the front wheel assembly  60  is provided in front of the front wheel moving part  50 , when the front wheel assembly  60  is moved back and forth by the front wheel  41 , the front wheel moving part  50  is also moved back and forth integrally with the front wheel assembly  60 . 
     The front wheel moving part  50  may include a front wheel moving base  53  and the front plate  54  disposed perpendicular to the front wheel moving base  53 . 
     The front wheel moving part  50  may include a linear motion member capable of guiding the linear movement of the front wheel assembly  60 . For example, a linear motion guide (LM guide)  55  may be used as the linear motion member. 
     A rail  55   a  of the LM guide  55  may be disposed on the front wheel moving base  53 . The rail  55   a  may be disposed on the front wheel moving base  53  perpendicular to a side wheel center line CL connecting the rotation center of the first side wheel  21  and the rotation center of the second side wheel  31 . 
     A block  55   b  of the LM guide  55  that is slidably coupled to the rail  55   a  may be fixed to the main frame  10 . Accordingly, the linear motion of the front wheel moving part  50  may be guided by the LM guide  55 . 
     The rear wheel moving part  80  may be formed to linearly move back and forth with respect to the main frame  10 . The rear wheel moving part  80  may be provided in the main frame  10  in parallel with the front wheel moving part  50  on one side of the front wheel moving part  50 . The rear wheel moving part  80  may have the same structure as the front wheel moving part  50 . 
     Because the rear wheel assembly  90  is provided at the rear end of the rear wheel moving part  80 , when the rear wheel assembly  90  moves back and forth, the rear wheel moving part  80  also moves back and forth integrally with the rear wheel assembly  90 . 
     The rear wheel moving part  80  may include a rear wheel moving base  83  and the rear plate  84  disposed perpendicular to the rear wheel moving base  83 . 
     The rear wheel moving part  80  may include a linear motion member capable of guiding the linear movement of the rear wheel assembly  90 . For example, a linear motion guide (LM guide)  85  may be used as the linear motion member. 
     A rail  85   a  of the LM guide  85  may be disposed on the rear wheel moving base  83 . The rail  85   a  may be disposed on the rear wheel moving base  83  perpendicular to the side wheel center line CL connecting the rotation center of the first side wheel  21  and the rotation center of the second side wheel  31 . 
     A block  85   b  of the LM guide  85  that is slidably coupled to the rail  85   a  may be fixed to the main frame  10 . The block  85   b  of the LM guide  85  of the rear wheel moving part  80  may be disposed on the main frame  10  to face the block  55   b  of the LM guide  55  of the front wheel moving part  50 . Accordingly, the linear motion of the rear wheel moving part  80  may be guided by the LM guide  85 . 
     In other words, the LM guide  55  of the front wheel moving part  50  and the LM guide  85  of the rear wheel moving part  80  are disposed in the main frame  10  parallel to each other. The front wheel assembly  60  may be linearly moved by the LM guide  55  of the front wheel moving part  50 , and the rear wheel assembly  90  may be linearly moved by the LM guide  85  of the rear wheel moving part  80 . 
     The wheelbase adjuster  20  may include a synchronizing device that allows the front wheel moving part  50  and the rear wheel moving part  80  to move the same distance in opposite directions. The synchronizing device may include a pair of racks (e.g., a front wheel rack  101  and a rear wheel rack  102 ) and at least one pinion (e.g., first, second, and third pinions  111 ,  112 , and  113 ). 
     The pair of racks may include a front wheel rack  101  disposed on the front wheel moving part  50  and a rear wheel rack  102  disposed on the rear wheel moving part  80 . 
     The front wheel rack  101  may be disposed on the front wheel moving base  53  in parallel with the LM guide  55  under the LM guide  55  of the front wheel moving part  50 . In detail, the front wheel rack  101  may be disposed under the rail  55   a  of the LM guide  55 . Accordingly, the front wheel rack  101  may move integrally with the front wheel moving part  50 . In other words, when the front wheel moving part  50  linearly moves back and forth with respect to the main frame  10 , the front wheel rack  101  also linearly moves back and forth with respect to the main frame  10 . 
     The rear wheel rack  102  may be disposed on the rear wheel moving base  83  in parallel with the LM guide  85  under the LM guide  85  of the rear wheel moving part  80 . In detail, the rear wheel rack  102  may be disposed under the rail  85   a  of the LM guide  85 . Accordingly, the rear wheel rack  102  faces the front wheel rack  101  in parallel, and is spaced apart from the front wheel rack  101  by a predetermined distance. 
     The rear wheel rack  102  may move integrally with the rear wheel moving part  80 . In other words, when the rear wheel moving part  80  linearly moves back and forth with respect to the main frame  10 , the rear wheel rack  102  also linearly moves back and forth with respect to the main frame  10 . 
     The at least one pinion may be disposed between the front wheel rack  101  and the rear wheel rack  102 . The at least one pinion may be disposed to engage both the front wheel rack  101  and the rear wheel rack  102 . Accordingly, the front wheel rack  101  and the rear wheel rack  102  may be interlocked through the at least one pinion. 
     In the case of this embodiment, three pinions, that is, a first pinion  111 , a second pinion  112 , and a third pinion  113  are provided between the front wheel rack  101  and the rear wheel rack  102 . The first, second, and third pinions  111 ,  112 , and  113  form a gear train. 
     The first pinion  111  meshes with the front wheel rack  101 , and the second pinion  112  meshes with the rear wheel rack  102 . The third pinion  113  is disposed between the first pinion  111  and the second pinion  112 , and meshes with the first pinion  111  and the second pinion  112 . The first, second, and third pinions  111 ,  112 , and  113  may be formed in the same standard. Therefore, when the front wheel rack  101  moves a certain distance in one direction, the rear wheel rack  102  also moves the same distance in the opposite direction through the first, second, and third pinions  111 ,  112 , and  113 . 
     In this embodiment, the wheelbase adjuster  20  does not include a separate driving source. The wheelbase adjuster  20  is configured so that when the front wheel  41  and the rear wheel  71  rotate, the front wheel moving part  50  and the rear wheel moving part  80  move linearly. 
     However, as another example, the front wheel moving part  50  and the rear wheel moving part  80  of the wheelbase adjuster  20  may be configured to be linearly moved by a separate driving source. For example, when a driving source is connected to at least one pinion (e.g., the first, second, and third pinions  111 ,  112 , and  113 ), the front wheel moving part  50  and the rear wheel moving part  80  may be simultaneously moved in opposite directions. 
     As another example, each of the front wheel moving part  50  and the rear wheel moving part  80  may be configured to be linearly moved by a separate driving source. 
     The front wheel torque transmitting device  40  may be formed to interlock the vertical movement of the front wheel  41  and the vertical movement of the first side wheel  21 . The front wheel torque transmitting device  40  may be configured to transmit the vertical movement of the front wheel  41 , i.e., the pivoting of the front wheel assembly  60 , to the first side wheel assembly  22 . The front wheel torque transmitting device  40  may be implemented mechanically or hydraulically. 
     For example, the front wheel torque transmitting device  40  may include a spline shaft  51  disposed in the front wheel moving part  50  and a pair of bevel gears (e.g., a first front wheel bevel gear  56  and a second front wheel bevel gear  66 ) connecting the front wheel moving part  50  and the front wheel assembly  60 . 
     The spline shaft  51  may be supported by a pair of bosses  52  spaced apart by a predetermined distance. The pair of bosses  52  may be fixed to the lower frame  12 . Because the lower frame  12  is fixed to the bottom surface of the main frame  10  through a plurality of fixing members  14 , the pair of bosses  52  are fixed to the main frame  10 . Accordingly, the spline shaft  51  may move linearly with respect to the main frame  10 . 
     In addition, the first upper frame  22   a  of the first side wheel assembly  22  may be pivotably connected to the spline shaft  51 . Accordingly, the spline shaft  51  may move linearly with respect to the first side wheel assembly  22 . 
     One end of the spline shaft  51  may be fixed to the front wheel moving base  53 . For example, one end of the spline shaft  51  may be fixed by a fixing bracket  51   a , and the fixing bracket  51   a  may be fixed to the front wheel moving base  53 . Therefore, when the front wheel moving base  53  moves, the spline shaft  51  may move integrally with the front wheel moving base  53 . 
     The spline shaft  51  may be disposed on the front wheel moving base  53  parallel to the rail  55   a  of the LM guide  55  above the rail  55   a . Accordingly, the linear motion of the front wheel moving part  50  may be guided by the spline shaft  51  and the LM guide  55 . 
     The pair of bevel gears (e.g., a first front wheel bevel gear  56  and a second front wheel bevel gear  66 ) may connect the front wheel moving part  50  and the front wheel assembly  60 . With this configuration, the front wheel moving part  50  may receive rotation by pivoting of the front wheel assembly  60  and transmit the rotation to the first side wheel assembly  22  while linearly moving back and forth with respect to the main frame  10 . 
     To this end, a first front wheel bevel gear  56  may be disposed at the leading end of the spline shaft  51 . For example, the first front wheel bevel gear  56  may be disposed at the leading end of the spline shaft  51  on one side of the fixing bracket  51   a . The front wheel assembly  60  may be provided with a second front wheel bevel gear  66  meshed with the first front wheel bevel gear  56 . 
     In detail, the second front wheel bevel gear  66  meshed with the first front wheel bevel gear  56  of the spline shaft  51  may be provided at the rear end of the front wheel assembly  60 . The second front wheel bevel gear  66  may be disposed to rotate on the fixed shaft  54   a  provided on the front plate  54 . In this case, the fixed shaft  54   a  of the front plate  54  and the spline shaft  51  form a right angle. 
     When the front wheel assembly  60  rotates upward at a predetermined angle about the fixed shaft  54   a  of the front plate  54 , the second front wheel bevel gear  66  rotates on the fixed shaft  54   a . When the second front wheel bevel gear  66  rotates, the first front wheel bevel gear  56  meshed with the second front wheel bevel gear  66  is rotated and applies a force to the spline shaft  51  in a downward direction. Then, because the first side wheel assembly  22  coupled to the spline shaft  51  receives a force in the downward direction, the first side wheel  21  disposed on the first side wheel assembly  22  is moved downward. In other words, the vertical movement of the first side wheel  21  and the vertical movement of the front wheel  41  may be interlocked with each other by the front wheel torque transmitting device  40 . 
     Therefore, when the front wheel assembly  60 , on which the front wheel  41  is disposed, turns upward to climb an obstacle such as the stairs, the first side wheel assembly  22  is moved downward by the front wheel torque transmitting device  40  so that the first side wheel  21  is in stable contact with the surface of the obstacle (e.g., the ground). Accordingly, the vehicle  1  for uneven terrain according to an embodiment may climb the obstacle stably. 
     The rear wheel torque transmitting device  70  may be configured to interlock the vertical movement of the rear wheel  71  and the vertical movement of the second side wheel  31 . The rear wheel torque transmitting device  70  may be configured to transmit the vertical movement of the rear wheel  71 , that is, the pivoting of the rear wheel assembly  90 , to the second side wheel assembly  32 . The rear wheel torque transmitting device  70  may be implemented mechanically or hydraulically. The rear wheel torque transmitting device  70  may have the same configuration as the front wheel torque transmitting device  40 . 
     For example, the rear wheel torque transmitting device  70  may include a spline shaft  81  disposed in the rear wheel moving part  80  and a pair of bevel gears (e.g., a first rear wheel bevel gear  86  and a second rear wheel bevel gear  96 ) connecting the rear wheel moving part  80  and the rear wheel assembly  90 . 
     The rear wheel moving part  80  may include the spline shaft  81 . The spline shaft  81  may be supported by a pair of bosses  82  spaced apart by a predetermined distance. The pair of bosses  82  may be fixed to the lower frame  12 . Because the lower frame  12  is fixed to the bottom surface of the main frame  10  through the plurality of fixing members  14 , the pair of bosses  82  are fixed to the main frame  10 . Accordingly, the spline shaft  81  may move linearly with respect to the main frame  10 . 
     In addition, the second upper frame  32   a  of the second side wheel assembly  32  may be pivotably connected to the spline shaft  81 . Accordingly, the spline shaft  81  may move linearly with respect to the second side wheel assembly  32 . 
     One end of the spline shaft  81  may be fixed to the rear wheel moving base  83 . For example, one end of the spline shaft  81  may be fixed by a fixing bracket  81   a , and the fixing bracket  81   a  may be fixed to the rear wheel moving base  83 . Therefore, when the rear wheel moving base  83  moves, the spline shaft  81  may move integrally with the rear wheel moving base  83 . 
     The spline shaft  81  may be disposed on the rear wheel moving base  83  parallel to the rail  85   a  of the LM guide  85  above the rail  85   a . Accordingly, the linear motion of the rear wheel moving part  80  may be guided by the spline shaft  81  and the LM guide  85 . 
     The pair of bevel gears (e.g., the first rear wheel bevel gear  86  and the second rear wheel bevel gear  96 ) may connect the rear wheel moving part  80  and the rear wheel assembly  90 . With this configuration, the rear wheel moving part  80  may receive rotation by pivoting of the rear wheel assembly  90 , and transmit the rotation to the second side wheel assembly  32  while linearly moving back and forth with respect to the main frame  10 . 
     To this end, a first rear wheel bevel gear  86  may be disposed at the leading end of the spline shaft  81 . For example, the first rear wheel bevel gear  86  may be disposed at the leading end of the spline shaft  81  on one side of the fixing bracket  81   a . The rear wheel assembly  90  may be provided with a second rear wheel bevel gear  96  meshed with the first rear wheel bevel gear  86 . 
     In detail, the second rear wheel bevel gear  96  meshed with the first rear wheel bevel gear  86  of the spline shaft  81  may be provided at the front end of the rear wheel assembly  90 . The second rear wheel bevel gear  96  may be disposed to rotate on a fixed shaft  84   a  provided on the rear plate  84 . In this case, the fixed shaft  84   a  of the rear plate  84  and the spline shaft  81  form a right angle. 
     When the rear wheel assembly  90  rotates upward at a predetermined angle about the fixed shaft  84   a  of the rear plate  84 , the second rear wheel bevel gear  96  rotates on the fixed shaft  84   a . When the second rear wheel bevel gear  96  rotates, the first rear wheel bevel gear  86  meshed with the second rear wheel bevel gear  96  is rotated and applies a force to the spline shaft  81  in a downward direction. Then, because the second side wheel assembly  32  coupled to the spline shaft  81  receives a force in the downward direction, the second side wheel  31  disposed on the second side wheel assembly  32  is moved downward. In other words, the vertical movement of the second side wheel  31  and the vertical movement of the rear wheel  71  may be interlocked with each other by the rear wheel torque transmitting device  70 . 
     Therefore, when the second side wheel assembly  32 , on which the second side wheel  31  is disposed, turns upward to climb an obstacle such as the stairs, the rear wheel assembly  90  is moved downward by the rear wheel torque transmitting device  70  so that the rear wheel  71  is in stable contact with the surface of the obstacle (e.g., the ground). Accordingly, the vehicle  1  for uneven terrain according to an embodiment may climb the obstacle stably. 
     Each of the front wheel assembly  60  and the rear wheel assembly  90  may be provided with a shock absorber. In detail, a front shock absorber  47  may be provided in the front wheel assembly  60 , and a rear shock absorber  77  may be provided in the rear wheel assembly  90 . 
     The front shock absorber  47  may be disposed between the front wheel moving part  50  and the front wheel assembly  60 . 
     Referring to  FIG. 8 , the front shock absorber  47  may include a damper  48  and a coil spring  49 . The lower end of the damper  48  may be fixed to the lower surface of the front wheel assembly  60 , that is, the lower front frame  60   b , and the upper end of the damper  48  may be pivotably connected to a damper bracket  48   a  fixed to the fixed shaft  54   a  of the front wheel moving part  50 . The coil spring  49  may be disposed outside of the damper  48 . In other words, the damper  48  may be disposed to be inserted into the coil spring  49 . 
     When the front shock absorber  47  is disposed between the front wheel assembly  60  and the front wheel moving part  50  as described above, a shock applied to the front wheel  41  may be absorbed, and the road surface followability of the front wheel  41  may be improved. 
     The rear shock absorber  77  may be disposed between the rear wheel moving part  80  and the rear wheel assembly  90 . The rear shock absorber  77  may be formed the same as or similar to the front shock absorber  47 . 
     Referring to  FIG. 9 , the rear shock absorber  77  may include a damper  78  and a coil spring  79 . The lower end of the damper  78  may be fixed to the lower surface of the rear wheel assembly  90 , that is, the lower rear frame  90   b , and the upper end of the damper  78  may be pivotably connected to a damper bracket  78   a  fixed to the fixed shaft  84   a  of the rear wheel moving part  80 . The coil spring  79  may be disposed outside of the damper  78 . In other words, the damper  78  may be disposed to be inserted into the coil spring  79 . 
     When the rear shock absorber  77  is disposed between the rear wheel assembly  90  and the rear wheel moving part  80  as described above, a shock applied to the rear wheel  71  may be absorbed, and the road surface followability of the rear wheel  71  may be improved. 
     The wheelbase adjuster  20  may include a locking device  100  configured to selectively fix the front wheel moving part  50  and the rear wheel moving part  80 . The locking device  100  may be disposed on the main frame  10 , and may be formed to selectively fix the front wheel moving part  50  and the rear wheel moving part  80  with respect to the main frame  10 . 
     When the locking device  100  operates to fix the front wheel moving part  50  and the rear wheel moving part  80 , the front wheel assembly  60  and the rear wheel assembly  90  may not move with respect to the main frame  10 . Accordingly, the wheelbase D between the front wheel  41  and the rear wheel  71  does not change. 
     When the locking device  100  is released, the front wheel assembly  60  and the rear wheel assembly  90  may linearly move back and forth with respect to the main frame  10 . Accordingly, the wheelbase D between the front wheel  41  and the rear wheel  71  may be changed. 
     Hereinafter, an example of the locking device  100  used in the vehicle  1  for uneven terrain according to an embodiment will be described in detail with reference to  FIGS. 10 to 12B . 
       FIG. 10  is a perspective view illustrating a locking device of a vehicle for uneven terrain according to an embodiment.  FIG. 11  is a partial bottom view illustrating racks and pinions of a locking device of a vehicle for uneven terrain according to an embodiment.  FIG. 12A  is a view illustrating a state in which a pinion of a locking device of a vehicle for uneven terrain according to an embodiment is locked so that the pinion is unable to rotate.  FIG. 12B  is a view illustrating a state in which a pinion of a locking device of a vehicle for uneven terrain according to an embodiment is released so that the pinion is able to rotate. For reference,  FIG. 11  is a partial bottom view viewed from the bottom up in a state in which the lower frame is removed to show the arrangement relationship of a pair of racks and at least one pinion of a vehicle for uneven terrain according to an embodiment. 
     Referring to  FIGS. 10 and 11 , the locking device  100  according to an embodiment may include a lifting stopper  120  and an actuator  130 . 
     The lifting stopper  120  may be formed to prevent the pair of racks (e.g., the front wheel rack  101  and the rear wheel rack  102 ) from moving by selectively blocking the rotation of at least one pinion (e.g., at least one of the first to third pinions  111 ,  112 , and  113 ) disposed in the wheelbase adjuster  20 . In other words, the lifting stopper  120  may be configured to selectively lock at least one pinion (e.g., at least one of the first to third pinions  111 ,  112 , and  113 ). 
     For example, the lifting stopper  120  may include a moving plate  121  and a fixed plate  122 . 
     The fixed plate  122  may be disposed to be fixed to the main frame  10 . In this embodiment, the fixed plate  122  is disposed under the actuator  130 , and is fixed with respect to the actuator  130 . 
     The moving plate  121  is disposed under the fixed plate  122  and is spaced apart from the fixed plate  122  by a predetermined distance. The moving plate  121  may be formed to move up and down with respect to the fixed plate  122 . In addition, the moving plate  121  may be disposed so that the moving plate  121  does not rotate with respect to the fixed plate  122 . 
     The moving plate  121  may move up and down with respect to the third pinion  113  by the actuator  130 . A plurality of coupling protrusions  123  may be provided on a bottom surface of the moving plate  121  in a circular shape. In other words, the plurality of coupling protrusions  123  may be spaced apart from each other at regular intervals along a circle having a predetermined diameter. 
     A plurality of elastic members  124  may be provided between the moving plate  121  and the fixed plate  122 . The plurality of elastic members  124  press the moving plate  121  downward to prevent the plurality of coupling protrusions  123  of the moving plate  121  from falling out of a plurality of coupling grooves  114  of the third pinion  113 . 
     The plurality of coupling grooves  114  may be provided on the upper surface of the third pinion  113 . The plurality of coupling grooves  114  may be arranged at regular intervals in a circular shape. The plurality of coupling grooves  114  may be formed in a shape corresponding to the plurality of coupling protrusions  123  of the moving plate  121 . 
     Accordingly, the plurality of coupling grooves  114  of the third pinion  113  may be engaged with the plurality of coupling protrusions  123  of the moving plate  121 . When the plurality of coupling protrusions  123  of the moving plate  121  are engaged with the plurality of coupling grooves  114  of the third pinion  113 , the third pinion  113  is unable to rotate. 
     The lifting stopper  120  may include an actuating part  125  and an actuating link  126  for actuating the moving plate  121 . 
     The actuating link  126  may connect the actuating part  125  and the actuator  130  so that the actuating part  125  may be rotated up and down by a predetermined angle by the actuator  130 . 
     The actuator  130  may be configured to move the lifting stopper  120  up and down. The actuator  130  may be fixed to the main frame  10  above the fixed plate  122 . The actuator  130  may include a rotation shaft  131  that rotates at a predetermined angle. As the actuator  130 , a rotating cylinder, a motor, or the like may be used. 
     The actuating part  125  may be formed to move the moving plate  121  up and down. For example, the actuating part  125  may be disposed under the moving plate  121  and formed in a substantially U-shape surrounding the plurality of coupling protrusions  123  of the moving plate  121 . Both ends of the actuating part  125 , that is, both ends of the U-shape may be pivotally disposed on the lower frame  12 . In other words, both ends of the actuating part  125  may be pivotally coupled to fixing bars  12   a  fixed to the lower frame  12 . Accordingly, the actuating part  125  may pivot a predetermined angle on both ends of the actuating part  125  coupled to the fixing bars  12   a.    
     A connecting portion  125   b  to which the actuating link  126  is connected may be provided at one end of the actuating part  125 , that is, at the lower end of the U-shape. The actuating link  126  may be rotatably connected to the connecting portion  125   b  of the actuating part  125 . 
     The actuating link  126  may be formed to connect the connecting portion  125   b  of the lower end of the actuating part  125  and the rotation shaft  131  of the actuator  130 . To this end, the actuating link  126  may be formed as a two-bar linkage. For example, the actuating link  126  may include a driving link  126   a  having one end connected to the rotation shaft  131  of the actuator  130 , and a driven link  126   b  having one end connected to the connecting portion  125   b  of the actuating part  125 . The other end of the driving link  126   a  and the other end of the driven link  126   b  are connected by a pin. Accordingly, the driving link  126   a  and the driven link  126   b  may rotate with respect to each other. 
     Accordingly, when the rotation shaft  131  of the actuator  130  rotates at a certain angle, the connecting portion  125   b  of the actuating part  125  is raised upward by the actuating link  126  as illustrated in  FIG. 12B . At this time, because both ends of the actuating part  125  are fixed to the lower frame  12 , the actuating part  125  pivots upward at a predetermined angle on the both ends of the actuating part  125 . 
     Then, the moving plate  121  is moved upward by the actuating part  125 , so that the plurality of coupling protrusions  123  of the moving plate  121  fall out of the plurality of coupling grooves  114  of the third pinion  113 . At this time, the plurality of elastic members  124  positioned between the moving plate  121  and the fixed plate  122  are compressed by the moving plate  121 . 
     When the plurality of coupling protrusions  123  of the moving plate  121  are separated from the plurality of coupling grooves  114  of the third pinion  113  as described above, the third pinion  113  is able to rotate freely. Accordingly, the front wheel rack  101  and the rear wheel rack  102  connected to the third pinion  113  through the first pinion  111  and the second pinion  112  may move freely. 
     In this case, because the front wheel moving part  50  in which the front wheel rack  101  is disposed and the rear wheel moving part  80  in which the rear wheel rack  102  is disposed are able to move, the front wheel assembly  60  connected to the front wheel moving part  50  and the rear wheel assembly  90  connected to the rear wheel moving part  80  may also move. Accordingly, when the front wheel  41  disposed in the front wheel assembly  60  and the rear wheel  71  disposed in the rear wheel assembly  90  move, the wheelbase D between the front wheel  41  and the rear wheel  71  may be adjusted. 
     In this state, when the rotation shaft  131  of the actuator  130  rotates by a predetermined angle in the opposite direction, as illustrated in  FIG. 12A , the actuating part  125  is lowered by the actuating link  126 . Then, the moving plate  121  is lowered so that the plurality of coupling protrusions  123  of the moving plate  121  are engaged with the plurality of coupling grooves  114  of the third pinion  113 . At this time, the plurality of coupling protrusions  123  of the moving plate  121  may be smoothly inserted into the plurality of coupling grooves  114  of the third pinion  113  by the elastic force of the plurality of elastic members  124 . 
     When the moving plate  121  is lowered by the actuator  130  so that the plurality of coupling protrusions  123  are engaged with the plurality of coupling grooves  114  of the third pinion  113 , the third pinion  113  is unable to rotate. Therefore, when the front wheel  41  and the rear wheel  71  rotate, the front wheel rack  101  of the front wheel moving part  50  and the rear wheel rack  102  of the rear wheel moving part  80  are unable to move. As a result, the wheelbase D between the front wheel  41  and the rear wheel  71  may not be adjusted. 
     In other words, as illustrated in  FIG. 12A , when the locking device  100  operates to lock the front wheel rack  101  of the front wheel moving part  50  and the rear wheel rack  102  of the rear wheel moving part  80 , the front wheel moving part  50  and the rear wheel moving part  80  may not move linearly with respect to the main frame  10 . Then, the front wheel assembly  60  connected to the front wheel moving part  50  and the rear wheel assembly  90  connected to the rear wheel moving part  80  may not move either. Accordingly, the wheelbase D between the front wheel  41  disposed in the front wheel assembly  60  and the rear wheel  71  disposed in the rear wheel assembly  90  does not change. 
     Conversely, as illustrated in  FIG. 12B , when the locking device  100  is released to allow the third pinion  113  to rotate, the front wheel rack  101  of the front wheel moving part  50  and the rear wheel rack  102  of the rear wheel moving part  80  may move along the third pinion  113 . Accordingly, the front wheel assembly  60  and the rear wheel assembly  90  may linearly move back and forth with respect to the main frame  10 . As a result, the wheelbase D between the front wheel  41  and the rear wheel  71  may change according to the rotation direction of each of the front wheel  41  and the rear wheel  71 . 
     In detail, when the front wheel  41  rotates in one direction, for example, in the counter-clockwise direction to move in front of the main frame  10 , that is, in a direction away from the main frame  10  and the rear wheel  71  rotates in the direction opposite to the front wheel  41 , for example, in the clockwise direction to move to the rear of the main frame  10 , that is, in a direction away from the main frame  10 , the front wheel assembly  60  and the rear wheel assembly  90  move forward and rearward of the main frame  10 , respectively, so that the wheelbase D between the front wheel  41  and the rear wheel  71  is increased. 
     Conversely, when the front wheel  41  rotates in the opposite direction, for example, in the clockwise direction to move in a direction closer to the main frame  10  and the rear wheel  71  rotates in the direction opposite to the front wheel  41 , for example, in the counter-clockwise direction to move in a direction closer to the main frame  10 , both the front wheel assembly  60  and the rear wheel assembly  90  move toward the main frame  10 , so that the wheelbase D between the front wheel  41  and the rear wheel  71  is reduced. 
     Hereinafter, a state in which the wheelbase D between the front wheel  41  and the rear wheel  71  in a vehicle  1  for uneven terrain according to an embodiment is maximized will be described with reference to  FIGS. 13 to 16 . 
       FIG. 13  is a perspective view illustrating a state in which a wheelbase of a vehicle for uneven terrain according to an embodiment is maximized.  FIG. 14  is a plan view of the vehicle for uneven terrain of  FIG. 13 .  FIG. 15  is a partial cross-sectional view illustrating the vehicle for uneven terrain of  FIG. 13  taken along line  FIG. 16  is a plan view illustrating a state in which a main frame is removed from the vehicle for uneven terrain of  FIG. 13 . 
     As illustrated in  FIGS. 13 to 16 , when the front wheel  41  rotates in one direction so that the front wheel assembly  60  linearly moves forward to the maximum with respect to the main frame  10 , the rear end of the front wheel moving part  50  connected to the front wheel assembly  60 , that is, the rear end of the front wheel moving base  53  contacts the block  55   b  of the LM guide  55 . In this state, the front wheel assembly  60  may not move further forward with respect to the main frame  10 . 
     In this case, the spline shaft  51  of the front wheel moving part  50  maintains a coupled state with one boss adjacent to the front wheel  41  among the pair of bosses  52  fixed to the lower frame  12 . In addition, the front wheel rack  101  of the front wheel moving part  50  maintains a state engaged with the first pinion  111  of the locking device  100 . 
     On the other hand, when the rear wheel  71  rotates in the opposite direction to the front wheel  41  so that the rear wheel assembly  90  linearly moves backward to the maximum with respect to the main frame  10 , the front end of the rear wheel moving part  80  connected to the rear wheel assembly  90 , that is, the front end of the rear wheel moving base  83  contacts the block  85   b  of the LM guide  85 . In this state, the rear wheel assembly  90  may not move further rearward with respect to the main frame  10 . 
     In this case, the spline shaft  81  of the rear wheel moving part  80  maintains a coupled state with one boss adjacent to the rear wheel  71  among the pair of bosses  82  fixed to the lower frame  12 . In addition, the rear wheel rack  102  of the rear wheel moving part  80  maintains a state engaged with the second pinion  112  of the locking device  100 . 
     In this state, when the locking device  100  operates to lock the front wheel rack  101  of the front wheel moving part  50  and the rear wheel rack  102  of the rear wheel moving part  80 , the front wheel assembly  60  and the rear wheel assembly  90  do not move relative to the main frame  10 . Therefore, the wheelbase D between the front wheel  41  and the rear wheel  71  may be maintained. 
     In this case, the distance between the first side wheel  21  and the second side wheel  31  may be kept constant. In other words, the distance between the first side wheel  21  and the second side wheel  31  does not change and remains the same in both the case where the wheelbase D between the front wheel  41  and the rear wheel  71  is the largest and the case where the wheelbase D therebetween is the smallest. 
     When it is desired to reduce the wheelbase D in a state in which the wheelbase D is maximum as illustrated in  FIG. 13 , the front wheel  41  and the rear wheel  71  are rotated in opposite directions. 
     In detail, the front wheel  41  rotates in the opposite direction, for example, in the clockwise direction to move to the rear of the main frame  10 , that is, in a direction closer to the main frame  10 , and the rear wheel  71  rotates in the opposite direction to the front wheel  41 , for example, in the counter-clockwise direction to move toward the front of the main frame  10 , that is, in a direction closer to the main frame  10 , so that the wheelbase D is reduced. 
       FIG. 17  is a block diagram illustrating a vehicle for uneven terrain according to an embodiment. 
     Referring to  FIG. 17 , a vehicle  1  for uneven terrain according to an embodiment may include a first side wheel driving motor  24 , a second side wheel driving motor  34 , a front wheel driving motor  42 , a front wheel steering motor  46 , a rear wheel driving motor  72 , a rear wheel steering motor  76 , a locking device  100 , an obstacle detector  210 , and a processor  200 . 
     The first side wheel driving motor  24  and the second side wheel driving motor  34  are electrically connected to the processor  200 . The first side wheel driving motor  24  and the second side wheel driving motor  34  rotate the first side wheel  21  and the second side wheel  31  under the control of the processor  200 , respectively. 
     The front wheel driving motor  42  and the rear wheel driving motor  72  are electrically connected to the processor  200 . The front wheel driving motor  42  and the rear wheel driving motor  72  rotate the front wheel  41  and the rear wheel  71  under the control of the processor  200 , respectively. 
     The front wheel steering motor  46  is electrically connected to the processor  200  and controls the moving direction of the front wheel  41  according to the control of the processor  200 . 
     The rear wheel steering motor  76  is electrically connected to the processor  200  and controls the moving direction of the rear wheel  71  according to the control of the processor  200 . 
     The locking device  100  is electrically connected to the processor  200 , and allows the front wheel moving part  50  and the rear wheel moving part  80  to be selectively fixed to the main frame  10  according to the control of the processor  200 . In detail, the actuator  130  of the locking device  100  is electrically connected to the processor  200  and operates under the control of the processor  200  so that the lifting stopper  120  may selectively lock the third pinion  113 . 
     When the actuator  130  raises the moving plate  121  of the lifting stopper  120 , the plurality of coupling protrusions  123  of the moving plate  121  are separated from the plurality of coupling grooves  114  of the third pinion  113 . Then, the third pinion  113  may rotate, so that the front wheel moving part  50  and the rear wheel moving part  80  may move back and forth with respect to the main frame  10 . 
     When the actuator  130  lowers the moving plate  121  of the lifting stopper  120 , the plurality of coupling protrusions  123  of the moving plate  121  engage with the plurality of coupling grooves  114  of the third pinion  113 . Then, the third pinion  113  is locked and may not rotate. As a result, the front wheel moving part  50  and the rear wheel moving part  80  may not move back and forth with respect to the main frame  10 . 
     The obstacle detector  210  is electrically connected to the processor  200  and is configured to detect the positions and sizes of obstacles to be climbed by the vehicle  1  for uneven terrain. The obstacle detector  210  may transmit information on the position and size of the detected obstacle to the processor  200 . 
     For example, the obstacle detector  210  may detect the position and size of the stairs to be climbed by the vehicle  1  for uneven terrain. The obstacle detector  210  may detect the size of the stairs and transmit the size information of the stairs to the processor  200 . The size information of the stairs may include a step height, a step width an edge interval, and a width of the stairs. 
     The obstacle detector  210  may be implemented using a three dimensional (3D) depth camera (or sensor), a 3D-light detection and ranging (LiDAR) sensor, or the like, capable of recognizing an obstacle in three dimensions. 
     As another example, the obstacle detector  210  may be implemented using two LiDARs capable of detecting line information. For example, after installing two LiDARs vertically, an obstacle may be extracted by combining line information detected by the two LiDARs. 
     The processor  200  may be configured to control the front wheel driving motor  42 , the rear wheel driving motor  72 , the first side wheel driving motor  24 , the second side wheel driving motor  34 , the front wheel steering motor  46 , and the rear wheel steering motor  76  to move the vehicle  1  for uneven terrain. 
     In addition, the processor  200  may be configured to adjust the wheelbase D between the front wheel  41  and the rear wheel  71  by controlling the locking device  100 , the front wheel driving motor  42 , and the rear wheel driving motor  72  according to the size information of the obstacle input from the obstacle detector  210 . 
     For example, when meeting the stairs, the processor  200  measures the size of the stairs using the obstacle detector  210 . The processor  200  may calculate the step height, the step width, and the edge interval of the stairs from the size information of the stairs input from the obstacle detector  210 , and may determine whether the stairs can be climbed with the current wheelbase D. Here, the edge interval of the stairs refers to the spacing between two adjacent edges measured on a straight line connecting the edges of a plurality of steps constituting the stairs. When the wheelbase D is equal to a multiple of the edge interval, the vehicle  1  for uneven terrain may not climb the stairs. 
     When it is determined that the vehicle  1  for uneven terrain is unable to climb the stairs because the current wheelbase D is short, the processor  200  controls the locking device  100 , the front wheel driving motor  42 , and the rear wheel driving motor  72  to increase the wheelbase D. 
     To this end, the processor  200  first operates the locking device  100  to allow the third pinion  113  to rotate. For example, the processor  200  may operate the actuator  130  of the locking device  100  to raise the moving plate  121 . When the moving plate  121  is raised, the plurality of coupling protrusions  123  of the moving plate  121  are separated from the plurality of coupling grooves  114  of the third pinion  113 , so that the third pinion  113  may rotate. 
     In this state, the processor  200  may control the front wheel driving motor  42  and the rear wheel driving motor  72  so that the front wheel  41  moves in front of the main frame  10  and the rear wheel  71  moves toward the rear of the main frame  10 . Then, the front wheel assembly  60  moves toward the front of the main frame  10  and the rear wheel assembly  90  moves toward the rear of the main frame  10  so that the wheelbase D between the front wheel  41  and the rear wheel  71  is increased. 
     When the wheelbase D 1  (see  FIG. 5 ) between the front wheel  41  and the first and second side wheels  21  and  23  is a multiple of about 1.4 to 1.5 of the edge interval of the stairs, the processor  200  stops the front wheel driving motor  42  and the rear wheel driving motor  72 . When the wheelbase D 1  between the front wheel  41  and the first and second side wheels  21  and  23  is a multiple of about 1.4 to 1.5 of the edge interval of the stairs, it may be prevented that the front wheel  41  and the first and second side wheels  31  and  32  are in contact with the vertical surfaces of the stairs at the same time. 
     In addition, because the front wheel  41  and the rear wheel  71  move the same distance, the wheelbase D 2  (see  FIG. 5 ) between the rear wheel  71  and the first and second side wheels  21  and  23  is equal to the wheelbase D 1  between the front wheel  41  and the first and second side wheels  21  and  23 . Accordingly, it may be prevented that the rear wheel  71  and the first and second side wheels  21  and  23  are simultaneously in contact with the vertical surfaces of the stairs. 
     Therefore, because the front wheel  41  and the side wheels  21  and  23  or the rear wheel  71  and the side wheels  21  and  23  do not contact the vertical surfaces of the stairs at the same time, the vehicle  1  for uneven terrain according to an embodiment may climb the stairs easily. 
     The processor  200  stops the front wheel driving motor  42  and the rear wheel driving motor  72  and then controls the locking device  100  to lock the third pinion  113  so that the third pinion  113  does not rotate. 
     For example, the processor  200  may operate the actuator  130  of the locking device  100  to lower the moving plate  121 . When the moving plate  121  is lowered, the plurality of coupling protrusions  123  of the moving plate  121  are engaged with the plurality of coupling grooves  114  of the third pinion  113 . When the plurality of coupling protrusions  123  of the moving plate  121  and the plurality of coupling grooves  114  of the third pinion  113  are engaged with each other, the third pinion  113  is locked and may not rotate freely. 
     Therefore, when the front wheel  41  and the rear wheel  71  rotate, the front wheel assembly  60  and the rear wheel assembly  90  do not move with respect to the main frame  10 , so the wheelbase D between the front wheel  41  and the rear wheel  71  does not change. 
     As described above, the vehicle for uneven terrain according to an embodiment may prevent the front wheel and the side wheels from simultaneously contacting the vertical surface of the stairs by adjusting the wheelbase between the front wheel and the rear wheel according to the size of the stairs. Therefore, the vehicle for uneven terrain according to an embodiment may easily climb stairs of various sizes. 
     Hereinabove, non-limiting example embodiments of the present disclosure have been described. It is to be understood that terms used herein are provided to describe example embodiments and do not limit the disclosure. Various modifications and alternations of example embodiments of the disclosure may be made according to the contents described above.