Patent Publication Number: US-6990757-B2

Title: Wheeled work vehicle

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a wheeled work vehicle including front and rear wheels and a swiveling ground-work implement. 
   2. Description of the Related Art 
   A conventional art of the above type is known from Japanese Patent Application “Kokai” No. 2001-97017. In this, a traveling body having front and rear wheels mounts a swivel base via a swivel bearing and the swivel base mounts thereon an upper structure having a driver&#39;s seat and a steering unit and mounts also a ground-work implement having a liftable work tool. An engine as a portion of the upper structure is mounted on the swivel base and the driver&#39;s seat is disposed immediately above a swivel shaft. With this conventional art, the top face of the traveling body is formed flat and located higher than upper ends of the front and rear wheels and the engine is mounted on the swivel base as described above. Hence, the upper structure includes a fuel tank, a work oil tank, a hydraulic unit etc. In operation, as the engine drives a hydraulic pump, the pump feeds its work oil to a traveling hydraulic motor mounted on the traveling body, so that the front and rear wheels are driven via a transmission mechanism. 
   The above-described conventional vehicle is capable of traveling at a high speed on the road with its front and rear wheels and capable also of effecting such ground work as digging with swiveling the ground-work implement and also lifting up/down its work tool. However, as the engine is mounted on the swivel base, the upper structure significantly projects rearward, thus presenting an extremely large distance from the swivel shaft to the rear end of the structure. Moreover, this rear end further projects significantly from the rear ends of the rear wheel. As a result, traveling stability cannot be obtained and also a swiveling operation within a limited space is very difficult. 
   Moreover, the swivel base mounts thereon not only the engine, but also other components as the fuel tank, the oil tank, the hydraulic unit, etc., so that the center of gravity of the vehicle is located at a relatively high level. This makes improvement in the traveling stability difficult. And, the significant total mass of the upper structure makes improvement in the swiveling operability difficult. 
   In addition, the ground-work implement can effect only vertical pivotal movements. Hence, even with swiveling of the swivel base, the ground work is possible only forwardly of the driver&#39;s seat. Hence, this conventional vehicle cannot cope with a work such as a side ditch digging for digging the ground near a wall or the like which is effected typically by a backhoe. Consequently, this conventional vehicle is disadvantageous in being limited in the type of work possible as well as in presenting significant difficulty in a digging operation within a limited space. 
   SUMMARY OF THE INVENTION 
   In view of the above, a primary object of the present invention is to provide a wheeled work vehicle capable of solving the above-described disadvantages of the prior art. More particularly, with the wheeled work vehicle proposed by the invention, the engine and engine-related components are mounted at a rear portion of the traveling body, thereby to achieve weight reduction in the upper structure as well as reduction in the dimension of the upper structure from the swivel bearing to the rear end of the structure. Further, the ground-work implement is made capable also of pivoting in the right/left direction. Moreover, the vehicle allows for improvement in the traveling stability and/or swiveling operability. 
   For accomplishing the above-noted object, a wheeled work vehicle, according to the present invention, comprises: 
   a traveling body including front and rear wheels, a traveling drive unit having an engine and a power transmission mechanism, a dozer unit disposed at least at a front portion of front and rear portions of the body, a fuel tank, a work oil tank, and a vehicle frame mounting said members of the traveling body; 
   a swivel base disposed upwardly of the traveling body and mounted via a swivel bearing on the traveling body to be swivelable for full-angle swiveling movement relative thereto; 
   a driver&#39;s seat mounted at a rear portion of the swivel base; 
   a steering unit disposed forwardly of the driver&#39;s seat; and 
   a ground-work implement supported on an implement support unit disposed erect on a front portion of the swivel base to be pivotable in the right/left direction; 
   wherein said vehicle frame includes an intermediate frame portion located between the front and rear wheels and supporting said swivel bearing and front and rear frame portions each located at a ground level higher than said intermediate frame portion; and 
   said front frame portion mounts a front-wheel suspension unit for the front wheels and said rear frame portion mounts a rear-wheel suspension unit for the rear wheels. 
   With this construction, the swivel base is disposed at a position lower than the highest position of the traveling body, whereby the swivel base can be swiveled for full angle relative to the body and also the traveling body is made positively heavier whereas the upper portion of the swivel base is made positively lighter. Further, the ground-work implement is supported to an upper portion of the swivel base and is made capable of pivoting in the right/left direction. Consequently, the construction achieves improvements in the traveling stability, ground-work stability, swiveling operability as well as compactness of the vehicle in both vertical and fore/aft directions. The construction also makes it possible to secure greater readiness in driver&#39;s getting on/off the vehicle as well as increased roominess for the driver and simplicity in the entire vehicle construction. 
   In order to realize the above-described characterizing features of the present invention, the invention further proposes a specific construction for the vehicle frame as the core component of the traveling body. In this, the vehicle frame includes right and left side frames, a front frame acting as a cross beam for interconnecting the right and left side frames at front portions thereof with a predetermined distance therebetween and a rear frame acting as a further cross beam for interconnecting the right and left side frames at rear portions thereof with a predetermined distance therebetween. Further, each of the two side frames includes an a horizontal intermediate portion located at an intermediate portion of the side frame, a horizontal rear portion located at a rear portion of the side frame and having a higher ground level than the intermediate portion, a horizontal front portion located at a front portion of the side frame and having a higher ground level than the intermediate portion, a rear transition portion connecting a rear end of the intermediate portion and the rear portion, and a front transition portion connecting a front end of the intermediate portion and the front portion. 
   More preferably, it is further proposed to increase a distance between the right and left intermediate portions relative to a distance between the front portions and also to a distance between the rear portions. Further, the front portions may have a higher ground level than the rear portions. All of these proposed constructions contribute to further reduction in the weight of the upper structure and reduction in the distance between the swivel bearing to the rear end of the upper structure, thus contributing to further improvement in the traveling stability and/or swiveling operability. 
   According to one preferred embodiment of the present invention, the traveling body mounts the fuel tank on one of right and left sides between the front and rear wheels and mounts the work oil tank on the other side of the same. This construction contributes to improvement in the weight balance of the traveling body in the right/left and fore/aft directions as well as in compact and reasonable arrangements of the fuel tank, the oil tank and the other mounted components. 
   According to a further preferred embodiment of the present invention, the fuel tank is mounted on either one of the right and left intermediate portions of the traveling body and the work oil tank is mounted on the other of the right and left intermediate portions. This facilitates mounting/dismounting of the fuel tank and the oil tank and the front and rear wheels to/from the traveling body. 
   According to a still further embodiment of the present invention, the engine is disposed at the rear portion of the traveling body and the power transmission mechanism is disposed at the intermediate portion of the traveling body. This construction allows for appropriate layout of the respective components constituting the traveling body according to the particular shapes thereof. 
   According to a still further embodiment of the present invention, the swivel bearing is disposed at a position lower than the upper ends of at least either the front or rear wheels. This construction allows the swivel base to be disposed at an even lower position, thereby to further lower the center of gravity of the entire wheeled work vehicle. 
   According to a still further embodiment of the present invention, the implement support unit pivotally supports a swing member of the ground-work implement via a swing shaft, the swing member pivotally supports a boom via a horizontal shaft and a boom cylinder for lifting up/down the boom is disposed rearwardly of the boom. With this construction, when the swivel base is swiveled, it is possible to prevent the ground-work implement from interfering with the traveling body and also to lower the position of the boom of the ground-work implement as much as possible. 
   According to a still further embodiment of the present invention, a front portion of the swing member projects radially outward from the swivel base and is set at a height which allows passage of the boom and the boom cylinder above the highest position of the traveling body. This construction serves to ensure sufficient free space for the driver on the swivel base and to allow the full-angle swiveling movement of the ground-work implement. 
   According to a still further embodiment of the present invention, a driver&#39;s seat mounting frame disposed on the swivel base includes a rear upward projecting portion projecting rearward and upward from the swivel base and the driver&#39;s seat and a ground-work implement manipulating unit are disposed on said rear upward projecting portion thereby to allow the driver&#39;s seat to pass above the traveling body when the swivel base is swiveled. This construction too serves to ensure sufficient free space for the driver on the swivel base and to allow the full-angle swiveling movement of the ground-work implement. 
   According to a still further embodiment of the present invention, each of the driver&#39;s seat mounting frame and the implement support unit mounted on the swivel base includes a pair of right and left front and rear attaching portions, to which front and rear ends of a ROPS (roll-over protection system) having a substantially angular hooked shape are connected. This greatly facilitates attachment of the ROPS. 
   Further and other features and advantages of the present invention will become apparent upon reading the following detailed description of preferred embodiments thereof in conjunction with accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view partially in section showing an embodiment of the invention in its entirety, 
       FIG. 2  is a plan view partially in section showing the embodiment, 
       FIG. 3  is a plan view partially in section showing a center portion of the embodiment, 
       FIG. 4  is a side view partially in section showing the center portion 
       FIG. 5  is a front view partially in section showing the embodiment, 
       FIG. 6  is an overall front perspective view, 
       FIG. 7  is an overall rear perspective view, 
       FIG. 8  is a central section view, 
       FIG. 9  is a plan view of a vehicle frame, 
       FIG. 10  is a side view of the vehicle frame 
       FIG. 11  is a rear view in section of a rear suspension unit, 
       FIG. 12  is a plan view in section of a transmission, 
       FIG. 13  is a side view in section showing a traveling transmission system, 
       FIG. 14  is a plan view showing a center portion of a traveling body, 
       FIG. 15  is a front view of a work oil tank, 
       FIG. 16  is a section view showing a swivel joint in its entirety, 
       FIG. 17  is a section view showing a lower portion of the swivel joint, 
       FIG. 18  is a perspective view showing a front portion of an upper structure, 
       FIG. 19  is a rear view of a steering unit, 
       FIG. 20  a side view of the steering unit, 
       FIG. 21  is a hydraulic circuit diagram of the entire work vehicle, and 
       FIG. 22  is a hydraulic circuit diagram of the transmission. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the invention will be described with reference to the accompanying drawings. 
   Referring to  FIGS. 1 through 7 , a wheeled work vehicle  1  includes, as its major components, a 4-wheeled type traveling body  4  having front and rear wheels  2 ,  3 , an upper structure  11  having a swivel base  6  mounted on the traveling body  4  via a swivel shaft (swivel axis)  5  and having also a driver&#39;s seat  7  and a steering unit  8  both mounted on the base  6 , a ground-work implement  9  mounted on the swivel base  6 , and front and rear dozers (acting also as stabilizers)  10 F,  10 R attached to front and rear portions of the traveling body  4 . 
   The traveling body  4  includes a traveling drive unit  12  having an engine  13  and a power transmission mechanism  14 , a vehicle frame  21 , front wheel suspension units  61 F suspending the front wheels  2  therefrom, rear wheel suspension units  61 R suspending the rear wheels  3  therefrom, and so on. The traveling body  4  mounts the engine  13  at a rear portion thereof and mounts selector valves  54  for hydraulic system at a front portion thereof. In the upper structure  11 , the steering unit  8  is disposed forwardly of the driver&#39;s seat  7 . 
   As shown in  FIGS. 2 ,  4 ,  5 ,  8 – 10 , the vehicle frame  21 , which presents a ladder-like shape in a plan view, includes a pair of right and left side frames  22  formed of angular pipes, front and rear plate-like frames  23 F,  23 R interconnecting front and rear portions of the opposed side frames  22 , a bearing support member  25  to which a swivel bearing  36  is attached, the bearing support member  25  interconnecting intermediate portions of the opposed side frames and a plurality of other connecting members for connecting the front and rear portions of the opposed side frames. Further, the right and left side frames  22  mounts, at their intermediate to rear portions thereof, the engine  13  and the power transmission mechanism  14  and mounts also a radiator  62  at rear portions thereof. The power transmission mechanism  14  is attached to the engine  13  and/or the right and left side frames  22 . 
   Here, according to essential features of the present invention, as may be apparent from  FIG. 1  and  FIG. 10 , the vehicle frame  21  include an intermediate frame portion located between the front and rear wheels  2 ,  3  and supporting the swivel bearing  36  and front and rear frame portions each located at a ground level higher than the intermediate frame portion. The front frame portion mounts the front wheel suspension units  61 F for the front wheels  2  whereas the rear frame portion mounts the rear wheel suspension units  61 R for the rear wheels  3 . To this end, as may be apparent from  FIG. 9  and  FIG. 10 , the vehicle frame  21  includes right and left side frames  22 , a front frame  23 F acting as a cross beam for interconnecting the right and left side frames  22  at front portions thereof with a predetermined distance therebetween and a rear frame  23 R acting as a further cross beam for interconnecting the right and left side frames  22  at rear portions thereof with a predetermined distance therebetween. Further, each of the two side frames  22  includes an a horizontal intermediate portion  22   a  located at an intermediate portion of the side frame, a horizontal rear portion  22   r  located at a rear portion of the side frame and having a higher ground level than the intermediate portion  22   a , a horizontal front portion  22   f  located at a front portion of the side frame and having a higher ground level than the intermediate portion  22 , a rear transition portion  22   ar  connecting a rear end of the intermediate portion  22  and the rear portion  22   r , and a front transition portion  22   af  connecting a front end of the intermediate portion  22  and the front portion  22   f . Further, a distance between the right and left intermediate portions  22   a  is greater than a distance between the opposed front portions  22   f  and greater also than a distance between the opposed rear portions  22   r . Further, the front portions  22   f  have a higher ground level than the rear portions  22   r.    
   Namely, in the side view of the vehicle frame  21 , in each of the right and left side frames  22 , the intermediate portion  22   a  is disposed downwardly of the swivel base  6  is located at the lowermost level, the rear portion  22   r  raised in the fore/aft direction from this intermediate portion  22   a  is located at a higher level and the front portion  22   f  raised also from the intermediate portion  22   a  is located at an even higher level, so that the vehicle frame  21  allows attachment of the front and rear wheel suspension units under the front and rear portions thereof, respectively. 
   More particularly, the top face of the intermediate portion  22   a  which is overlapped with the swivel base  6  mounted on the vehicle frame  21  is set lower than the top faces of the front and rear portions and the bottom faces of the front and rear portions are set higher than the bottom face of the intermediate portion  22   a . With these arrangements, compared with a conventional vehicle frame which is formed flat entirely, the swivel base  6  can be disposed at a lower level, thus reducing a ground-level difference between the swivel base  6  and the front and rear suspension units  61 F,  61 R, whereby the center of gravity of the vehicle is lowered advantageously. 
   Further, in the plan view of the vehicle frame  21 , in the right and left side frames  22 , the opposed intermediate portions  22   a  overlapped with the swivel base  6  are formed wider in the right/left direction than the opposed front portions and also the opposed rear portions. In addition, each side frame  22  is bent at two positions in the fore/aft direction and then extends outward therefrom, so that the side frame presents a trapezoidal shape. 
   In the right and left side frames  22 , the opposed intermediate portions  22   a  form the distance, i.e. right/left-wise width, greater than that of the front portions and that of the rear portions as described above. And, to top and bottom faces of border portions between the intermediate portion  22   a  and the front and rear portions, there are attached reinforcing plates  22   b.    
   In the ladder-like shaped vehicle frame  21  described above, the intermediate portions  22   a  extend outward in the right/left directions from the front and rear portions and also the right and left sides of the frame are located radially inside the outer periphery of the swivel base  6  and also radially outside the outer periphery of the swivel bearing  36 . So that, the swivel bearing  36  is confined within and vertically overlapped with the area delimited between the opposed intermediate portions  22   a  of the vehicle frame  21 , thereby to allow for the lower-level mounting of the swivel base  6 . 
   The vehicle frame  21  thus constructed provides a rigid and strong structure capable of sufficiently supporting the upper load as well as withstanding load in the fore/aft direction. And, as the intermediate portions  22   a  are formed lower than the front and rear portions, the swivel bearing  36  and the swivel base  6  can be disposed at lower positions than the upper ends of the front and rear wheels  2 ,  3 . 
   As may be seen from  FIGS. 2 and 3 , each front wheel suspension unit  61 F includes a cylindrical hollow front axle case (differential case)  63 F and a front wheel differential unit  64 F accommodated therein. The right-to-left center of this front axle case  63 F is supported to the front lower portion of the vehicle frame  21  via a center pin  65 F extending in the fore-and-aft direction, thereby to allow the right and left ends of the unit to be vertically pivotable. Further, at a right or left end of the front axle case  63 F, there is provided a bevel gear case  66 F for supporting a king pin, and to this bevel gear case  66 F, there is provided a front wheel transmission case  67 F to be pivotable about the king pin, and the front wheel  2  is mounted on an axle  68 F supported to this front wheel transmission case  67 F. With this, the right and left front wheels  2  are steerable via the respective front wheel transmission cases  67 F by a steering means  69 . 
   Like the front wheel suspension unit  61 F described above, as shown in  FIGS. 3 and 11 , each rear wheel suspension unit  61 R includes a cylindrical hollow rear axle case  63 R and a rear wheel differential unit  64 R accommodated therein. To the right or left end of the rear axle case  63 R, there is provided a bevel gear case  66 R supporting a king pin  66   a . This bevel gear case  66 R includes a rear wheel transmission case  67 R to be pivotable about the king pin  66   a  and the rear wheel  3  is mounted on an axle  68 R supported to this rear wheel transmission case  67 R. With this, the right and left rear wheels  3  are steerable via the respective rear wheel transmission cases  67 R by the rear steering means  69 . 
   Like the front wheel suspension unit  61 F, the rear wheel suspension unit  61 R also may be constructed such that the right-to-left center of the rear axle case  63 R is supported for allowing, via a center pin provided at a rear lower portion of the vehicle frame  21  extending in the fore-and-aft direction, the right and left ends of the unit to be vertically pivotable. In this embodiment, however, the rear axle case  63 R is fixed to the vehicle frame  21 . 
   Referring to the rear wheel suspension unit  61 R, the rear axle case  63 R comprises right and left separate members which are coupled via a flange portion  93   a  in abutment with each other. One separate member accommodates therein a rear wheel differential unit  64 R inserted from the end therefor where the flange portion  93   a  is formed and supports a bevel pinion shaft  86 R inserted therein for receiving power from the power transmission mechanism  14 . 
   In one rear axle case  63 R, a pair of bearings  95 B,  95   c  are supported within a cylindrical hole  95   a . These bearings  95   b ,  95   c  support a differential case  95   d . This differential case  95   d  mounts at an end thereof a differential large gear  95   e  meshing with the bevel pinion shaft  86 R. This differential large gear  95   e  is supported by the one bearing  95   b  also. From the differential case  95   d , a differential yoke shaft  70  extends outwards to the right and to the left. 
   Each of the right and left rear axle cases  63 R includes, at outer ends thereof, brake portions  63   a  and a differential lock portion  63   b  formed more inward than the brake portions  63   a . At an outer end of each of the right and left brake portions  63   a , the bevel gear case  66 R is secured and to this bevel gear case  66 R, there is attached the rear wheel transmission case  67 R supporting the rear wheel  3  via the axle  68 R. 
   The differential yoke shaft  70  extends through from the rear wheel differential unit  64 R into the right and left bevel gear cases  66 R. Between this differential yoke shaft  70  and the brake portions  63   a , there is disposed a hydraulic brake mechanism A and between the differential yoke shaft  70  and the differential lock portion  63   b , there is disposed a hydraulic differential lock mechanism  177 . 
   The bevel gear case  66 R is connected to the outer end of the brake portion  63   a  through a faucet-like joint and supports via a bearing a bevel gear  96   a  fitted on the outer end of the differential yoke shaft  70  and supports also a bevel gear  96   b  fitted on the upper end of the king pin  66   a  and meshed with the bevel gear  96   a.    
   The rear wheel transmission case  67 R is supported to a lower potion of the bevel gear case  66 R via a pair of bearings  96   c  to be pivotable about the king pin  66   a  and its upper portion too is pivotally supported to an upper portion of the bevel gear case  66 R. 
   This rear wheel transmission case  67 R supports the axle  68 R and supports also the bevel gear  96   d  fitted on a lower portion of the king pin  66   a  for meshing with the bevel gear  96   e  fitted on the axle  68 R. 
   The bevel gear case  66 R and the rear wheel transmission case  67 R together constitute a final reduction case mounted on the outer end of each of the right and left rear axle cases  63 R and the two sets of bevel gears  96   a ,  96   b ,  96   d ,  96   e  accommodated therein together constitute a final reduction mechanism. 
   The brake portion  63   a  houses therein a piston A 2  for pushing a disc A 1  of the brake mechanism A into an engaging portion  66   b  of the bevel gear case  66 R. In operation, as the piston A 2  is pushed by an oil pressure externally supplied, the disc A 1  is pushed into the engaging portion  66   b  of the bevel gear case  66 , thereby to brake the differential yoke shaft  70 . Incidentally, the disc A 1  may be directly pushed into the engaging portion  66   b  of the bevel gear case  66 R. But, an abutment plate may be provided or the piston A 2  may be disposed on the side of the engaging portion  66   b  so that the disc A 1  is pushed toward the rear axle case  63 R. 
   The differential lock mechanism  177  includes an engaging member  177   a  fixed to the differential case  95   d , a movable engaging member  177   b  provided on the differential yoke shaft  70  to be rotatable therewith and movable relative thereto, a hydraulic means  177   c  for pushing the movable engaging member  177   b  toward the engaging member  177   a  for engagement therewith and an urging means  177   d  for urging the movable engaging member  177   b  away from the engaging member  177   a . Hence, upon engagement between the movable engaging member  177   b  and the engaging member  177   a , the differential case  95   d  and the differential yoke shaft  70  are rotated in unison. 
   As the differential lock mechanism  177  has a relatively small outer diameter, the differential lock portion  63   b  of the rear axle case  63 R projects radially inward and is smaller than the cylindrical hole  96   b . For this reason, the rear wheel differential unit  64 R and the brake mechanism A can be fixed in position in one direction. 
   The other separate member does not support the rear wheel differential unit  64 R or the bevel pinion shaft  86 R. However, the brake mechanism A of the brake portion  63   a  and the differential lock mechanism  177  of the differential lock portion  63   b  of the other separate member are substantially same as those of the one separate member described above. 
   As shown in  FIG. 3 , the right and left rear axle cases  63 R include cylinder attaching portions  63   a  projecting in opposition to each other and a hydraulic steering cylinder  71  of the steering means  69  is attached to these cylinder attaching portions  63   c . The connection between the right and left rear axle cases  63 R functions also as the attachment of the cylinder  71 . 
   The steering means  69  includes the hydraulic cylinder (power steering cylinder)  71  provided in the rear axle case  63 R and a tie rod  72  interconnecting opposed ends of a piston rod  71   a  of the hydraulic cylinder  71  and the right and left rear wheel transmission cases  67 R, so that with a movement of the piston rod  71   a  to the right or left the steering means  69  pivots the right and left rear wheel transmission cases  67  about the king pin  66   a , thereby to steer the rear wheels  3 . 
   To the left rear wheel transmission case  67 R, there is fixed an arm  120  and a first coupling rod  121  is connected to this arm  120 . Numeral  122  denotes a moving body having an intermediate portion thereof pivotally supported via a vertical shaft to the intermediate portion  22   a  of the left side frame  22 . To opposed ends of this moving body  122 , there are connected one end of the first coupling rod  121  and one end of a second coupling rod  123 , respectively. The other end of the second coupling rod  123  is connected to an arm  124  provided in the left front wheel transmission case  67 F for the front wheel  2 . Knuckle arms  125  of the right and left front wheel transmission cases  67 F are interconnected via a tie rod  126 . 
   With the steering means  69  in operation, when the rear wheels  3  are steered by the actuation of the hydraulic cylinder  71 , the front wheels  2  are also steered through the moving body  122  and the first and second coupling rods  121 ,  123 . In this, the front wheels  2  and the rear wheels  3  are steered in opposite directions. Instead, the front and rear wheels  2 ,  3  may be steered in a same direction. 
   The traveling body  4  is a two-shaft, four-wheel drive construction in which the power is transmitted from the traveling drive unit  12  to both the front wheel differential unit  64 F and the rear wheel differential unit  64 R and is also a four-wheel steering type construction in which the front and rear wheels  2 ,  3  are steerable in opposite directions (or may be in a same direction) via the front and rear steering means  69 F,  69 R in response to a steering operation by a single steering wheel  73 . 
   However, the traveling body  4  may alternatively be constructed such that either the front wheels  2  or the rear wheels  3  alone are provided as the drive and steerable wheels with the other as driven and non-steerable, i.e. straight traveling, wheels. Further alternatively, the structure may be constructed such that either the front wheels  2  or the rear wheels  3  alone are constantly driven and steered and the other are driven and steered only when needed. 
   Further, in the illustrated embodiment, the front and rear wheels  2  and  3  have substantially same diameter. Instead, one of them may have a greater or different diameter than the other. 
   As shown in  FIGS. 1 ,  2 ,  6  and  7 , at the front and rear portions (front and rear frames  23 F,  23 R) of the traveling body  4 , in order to mount respective dozers  10 F,  10 R at each of these portions, a pair of right and left upper arm supports  74 U, lower arm supports  74 D and a central upper cylinder support  75  project forwardly. 
   Each dozer  10 F,  10 R includes a blade  76 , a pair of right and left arms  77 U attached to an upper portion of the rear face of the blade  76  and pivotally supported to the upper arm supports  74 U to be liftable about horizontal axes, and an operational cylinder  78  supported to the cylinder support  75  for lifting the dozer  10  up and down so as to bring the blade  76  into contact with the ground surface or insert it into the ground. 
   This dozer  10 F,  10 R has a substantially same construction and substantially same function as a dozer device of a backhoe. However, if the ground-work implement  9  is used mainly for ground excavating work, then, the main function of the dozer is that of a stabilizer for the traveling body  4  (i.e. function as an outrigger). The dozer may be provided only one of the front and rear portions of the traveling body  4 . In this embodiment, however, two of them are provided at the front and the rear portions so that the dozers may lift the traveling body  4  up off the ground during a work. 
   As may be seen from  FIGS. 1 ,  2 ,  5 – 8 ,  14  and  15 , on right and left sides (side frames  22 ) of the traveling body  4  and between the front and rear wheels  2 ,  3 , there is disposed a fuel tank  16  on one side (left side) and there are disposed a work oil tank  17  and a battery  18  behind it on the other side (right side). The right and left arrangement of these tanks, i.e. the fuel tank  16  and the work oil tank  17  may be reversed. In either case, with this right and left distribution of the tanks, the right and left weight balance of the traveling body  4  is improved and also the space between the front and rear wheels  2 ,  3  is efficiently utilized. 
   As described above, the fuel tank  16  and the work oil tank  17  plus the battery  18  are arranged in the right and left distribution on the vehicle frame  21 . The work oil tank  17  is detachably mounted on the right side frame  22  and has a substantially L-like shape in front view and includes an extension portion  17   a  extending under the right side frame  22 . Within this extension portion  17   a , an oil filter  130  is disposed and there is formed an L-shaped (in plan view) recess  17   b  for disposing the battery  18 . 
   The recess  17   b  is formed at a rear and right-to-left wise inner portion of the work oil tank  17 . Then, as the battery  18  is disposed therein, the battery  18  is covered by the work oil tank  17  from the outer side and the front side. 
   At a front lower portion of the work oil tank  17 , there is formed a keyhole-shaped opening  128  comprising large and small holes  128   a ,  128   b  connected in series. A cover member  129  for closing this opening  128  too has a keyhole-like shape This cover member  129  defines a small-hole corresponding portion  129   a  to which the oil filter (suction filter)  130  and a suction pipe  131  communicating therewith are connected. The suction pipe  131  extends under the side frame  22  to be connected with various valves. 
   The oil filter  130  as being attached to the cover member  129  is inserted from the large hole  128   b  to the small hole  128   a , thereby to allow attachment of the cover member  129  in correspondence with the keyhole opening. In this way, maintenance operation is facilitated through the facilitation of insertion of the oil filter  130  into the opening  128 . 
   Numeral  132  denotes an outlet pipe which extends from a pump  133  of the work oil tank  17  and under the battery  18  and the side frame  22  to be eventually connected with the hydraulic pump for the engine  13 . 
   On the top of the right side frame  22 , there are provided erect a plurality of retaining pins  134   a  for allowing temporary retention of the work oil tank  17  by these retaining pins  134   a . These retaining pins  134   a  and apertured retaining members  134   b  provided in the work oil tank  17  to be retained thereto together constitute tank temporary fixing means  134 . 
   Further, the work oil tank  17  temporarily fixed by the temporary fixing means  134  can then be fixed permanently by a permanent attaching means  136 . This permanent fixing means  136  includes a rod  135   d  extending in the fore-aft direction and retained by a substantially L-shaped (in front view) retained member  135   e  fixed on the top face of the work oil tank  17  and a retaining member  135   a  to be fastened to opposed ends of the rod  135   d  by means of nuts  135   e . Then, the lower end of the retaining member  135   a  is hooked to the apertured retaining member  139   a  attached to the right side frame  22  and a bracket  139   b  and then the nuts  135   e  are fastened, whereby the work oil tank  17  is drawn toward the right side frame  22 . With this, the permanent attachment is completed. 
   The permanent attaching means  136  may alternatively be constructed such that the work oil tank  17  is fixed to the right side frame  22  by means of fastening members such as bolts. 
   Between the bottom face of the right side frame  22  and the extension portion  17   a , there is provided a cushion member  137  formed of e.g. rubber, so that the work oil tank  17  may be supported with its top face being oriented substantially horizontal. 
   The work oil tank  17 , as denoted with two-dot lines in  FIG. 8 , is covered with a cover  138  having an outer face and an upper face which are substantially reversed-L shaped in the front view. This cover  138  is formed of a metal plate or plastic and is attached via e.g. a mount to the front and rear portions of the work oil tank  17  by brackets  139   b  fixed to the right side frame  22 . The upper horizontal portion of this cover  138  provides a step portion  138 A. 
   The fuel tank  16  is formed of plastic or plate metal and is fixed to the outer face of the left side frame  22 . 
   More particularly, to the outer face of the left side frame  22 , there are attached a pair of front and rear brackets  190  extending outward in the right and left directions, and to and between these front and rear brackets  190 , the fuel tank  16  is attached. 
   This fuel tank  16 , like the work oil tank  17  described above, may have a substantially L-shape (in plan view) having an extension portion extending under the side frame  22 , so that the tank may be attached via a tank temporary retaining means and tank permanent attaching means. 
   Further, like the work oil tank  17 , the top face and the outer face of the fuel tank  16  are covered with a cover  191 . This cover  191  is attached to the brackets  190  via mounts  190   a . The top horizontal portion of this cover  191  provides a step portion  191 A. 
   Incidentally, the covers  138 ,  191  may be provided as flat plates covering only the top faces of the tanks  17 ,  16  and/or may be secured to the tanks  17 ,  16 . 
   As shown in  FIGS. 1–4 ,  6 ,  7 ,  12  and  13 , the traveling body  4  has a portion thereof downwardly of the swivel base  6  provided as a flat portion  4 A and a further portion thereof rearwardly of the swivel base  6  as a raised portion  4 B. To this raised portion  4 B, an engine hood  80  is detachably attached to be opened and closed. 
   Within the engine hood  80  attached to the raised portion  4 B of the traveling body  4 , the engine  13  is mounted and in the flat portion  4 A thereof, the power transmission mechanism  14  is mounted. And, the swivel base  6  is disposed upwardly of the flat portion  4 A housing the power transmission mechanism  14 . The engine  13  projects downwardly of the swivel base  6 . 
   The engine  13  may be disposed with the axis of its crank shaft  13 A being oriented along the right and left direction. In this case, however, the engine  13  is disposed along the fore and aft direction, with the right-and-left center  13 S (see  FIG. 3 ) thereof being substantially aligned with or slightly offset to one side (left side) from the right-and-left center of the vehicle frame  21  (extending through a center  5 S of the swivel shaft  5 ). 
   The radiator  62  disposed rearwardly of the engine  13  may alternatively be disposed at the right-and-left center of the vehicle frame  21 . In this case, however, the radiator  62  is disposed with offset to the same side as the engine  13 . 
   The power transmission mechanism  14  disposed at the flat portion  4 A can be a mechanical transmission mechanism. In this case, however, this mechanism  14  is provided as combination of a hydrostatic transmission (HST)  26  including a pump  81  and a motor  82 , and a reduction device  87 . As shown in  FIGS. 3 ,  4 ,  12  and  13 , a transmission case  83  for this hydrostatic transmission  26  supports an input shaft  27  for the pump  81  for receiving the power from the engine  13  and an output shaft  28  of the motor  82 . And, these shafts are respectively aligned substantially with the fore and aft direction in the plan view. The transmission case  83  of the transmission  26  and front and rear cases  87 A,  87 B of the reduction device  38  are assembled together and the input shaft  27  and the output shaft  28  are disposed with slightly forward-downward inclination in the side view thereof. 
   The reduction device  87  accommodates, inside the front and rear cases  87 A,  87 B thereof, two sets of reduction gears  107 ,  108 . Each of the front and rear cases  87 A,  87 B has a short vertical width and a long right-and-left width. The front case  87 A includes a charge pump  109  and a hydraulic clutch  110  controlled by this charge pump  109 . 
   The input shaft  27  projects forwardly and rearwardly from the transmission case  83 , with its rear portion being coupled via a flywheel to the crank shaft  13 A and its front portion is supported to the rear case  87   b  of the reduction device  87  and mounts a gear  107 A of the reduction gear set  107  and is operable for driving the charge pump  109 . 
   The gear  107 A of the reduction gear set  107  is meshed with a gear  107 B and this gear  107 B is mounted on a clutch input shaft  111  of the hydraulic clutch  110 . Between this clutch input shaft  111  and a clutch output shaft  112  of the hydraulic clutch  110 , there is provided a clutch means  113  which can be engaged/disengaged by the pressure oil fed from the charge pump  109 . 
   The clutch output shaft  112  drives, via a universal joint shaft, the hydraulic pump  85  for feeding work oil of a large load. 
   The charge pump  109  is comprised of e.g. a trochoid pump. When the engine  13  is driven, this pump  109  feeds the pressure oil of a predetermined pressure to the clutch means  113  to keep it engaged. When the engine  13  is stopped, the charge pump  109  is also stopped, thereby to disengage the clutch means  113 . Accordingly, for a start-up of the engine  13 , this may be done without applying the load from the hydraulic pump  85  to the clutch output shaft  112 . Hence, the start-up load can be reduced advantageously. 
   The output shaft  28  of the motor  82  mounts a gear  108 A of the reduction gear set  108 . This gear  108 A is meshed with a gear  108 B mounted on a propelling shaft  114 . The propelling shaft  114  projects forwardly and rearwardly of the front and rear cases  87 A,  87 B of the reduction device  87  to be connected respectively via front and rear universal joint shafts  29 F,  29 R to bevel pinion shafts  86 F,  86 R of the front differential unit  64 F and the rear differential unit  64 R. 
   In this way, by using the front and rear universal joint shafts  29 F,  29 R for power transmission to the front and rear wheels  2 ,  3 , even if the bevel pinion shafts  86 F,  86 R are offset in the right-and-left direction from the center pin  65 , or the propelling shaft  114  is inclined downward forwardly, the power transmission to the front and rear differential units  64  is still allowed and the vertical pivotal movements of the front axle cases  63 F are allowed also. 
   In  FIGS. 1 through 7 , the traveling body  4  mounts thereon the swivel bearing  36  for swivelably supporting the swivel base  6 , a ring gear  88  attached along the inner periphery of the swivel bearing  36 , a drive pinion  89  meshing with this ring gear  88 , and a hydraulic swivel motor  15  for driving the drive pinion  89  for swiveling the swivel base  6 . 
   The swivel shaft  5  mounted at the center  5 S of the swivel bearing  36  is constructed as a swivel joint, so that connections of work oil passages connecting the hydraulic pump  85  to the ground-work implement  9 , pilot oil passages connecting the manipulating unit and selector valves, electric cables interconnecting the steering unit  8  and the traveling drive unit  12  and so on can be carried out even during the swiveling movement of the swivel base  6 . 
   The above-described components including the swivel motor  15 , the universal joint shafts  29 , and the hydraulic pump  85  constitute some parts of the power transmission mechanism  14  of the traveling drive unit  12 . And, these components are disposed at a level lower than the top face of the vehicle frame  21  and higher than the bottom end of the engine  13  in a compact manner not only in the vertical direction, but also in the fore-and-aft and right-and-left directions. 
   The components including the swivel base  6 , the driver&#39;s seat  7  disposed at the rear upper portion of the swivel base  6  of the swivel shaft  5 , the steering unit  8  disposed at the front portion of the swivel base  6  forwardly of the driver&#39;s seat  7 , the manipulating unit  55  disclosed around the driver&#39;s seat  7  for manipulating the ground-work implement  9  and so on together constitute the upper structure  11 . 
   The center  5 S of the swivel shaft  5  is slightly offset to the forward side from the center P of the axes of the front and rear wheels  2 ,  3 . And, relative to this swivel shaft  5 , the operator&#39;s seat  7  is disposed on the rear side of the swivel base  6  and the steering unit  8  and the ground-work implement  9  are disposed on the forward side thereof, respectively. The front end of the upper structure  11  is constructed as the steering unit  8  and the rear portion thereof is constructed as the driver&#39;s seat  7 , and a hydraulic control valve  56  of the manipulating unit  55  is disposed rearwardly of the driver&#39;s seat  7 . 
   In the upper structure  11 , the swivel bearing  36  and the swivel base  6  are disposed lower than the upper end of the engine  13  disposed at the rear portion of the traveling body  4 , and of the swivel bearing  36  and the swivel base  6 , at least the swivel baring  36  is disposed at a position between the front and rear wheels  2 ,  3  and lower than the upper ends of at least either one of the front and rear wheels  2 ,  3 . 
   In its plan view, the swivel base  6  is flat at its front portion and is substantially circular at its rear and right and left side portions. The rear portion is disposed adjacent the engine  13 . When the base  6  is oriented forwardly, the front portion is substantially aligned with the rear ends of the right and left front wheels  2 . When the base  6  is swiveled, its outer periphery becomes overlapped in the fore-and-aft direction with the rear ends of the right and left front wheels  2 . And, this swivel base  6  projects sideways to the right and left from the vehicle frame  21  to be overlapped in the right and left direction with the fuel tank  16  and the work oil tank  17 , respectively. 
   That is, the swivel base  6  is formed such that it has a progressively larger area defined by three points of the engine  13  disposed substantially right-and-left center and the pair of front wheels  2  disposed apart therefrom on the right and left sides. Or, after securing a necessary area for the swivel base  6 , the fore-and-aft dimension and the right-and-left dimension of the traveling body  4  are set as compact as possible. 
   And, since the traveling body  4  mounts thereon such components as the engine  13 , the fuel tank  16 , the work oil tank  17 , the selector valves  54  etc., this traveling body  4  has a significant weight, whereby the weight of the upper structure  11  is reduced correspondingly and its fore-and-aft and right-and-left dimensions may also be small. 
   With the above-described construction, relative to the weight of the traveling body  4  having the front and rear wheels  2 ,  3 , the total weight of those components mounted therein such as the swivel base  6 , the driver&#39;s seat  7  on the swivel base  6 , the steering unit  8  and the ground-work implement  9 , or the total weight of at least the swivel base  6  and the driver&#39;s seat  7  and the steering unit  8  mounted thereon may be smaller. 
   Further, the arrangement of the power transmission mechanism  14  around the swivel shaft  5  and also the above-described triangular arrangement of the engine  13 , the fuel tank  16  and the work oil tank  17 , etc. all help improve the weight balance around the swivel shaft  5 . Further, as the engine  13  is disposed at the rear portion of the traveling body  4 , the selector valves  54  are disposed at the front portion and the work oil tank  17  and the fuel tank  16  are disposed on the right and left sides thereof, the weight balance in all directions is improved. 
   The gravity center Q of the work vehicle  1  is located slightly forwardly of the center  5 S of the swivel shaft  5  and adjacent the rear end of the hydraulic pump  85  in the fore/aft direction and is located also adjacent the top faces of the swivel base  6  and the swivel bearing  36  in the right/left direction. Further, in the right/left direction, this gravity center Q is located at a position slightly offset to the right relative the center  5 S and overlapped with the swivel motor  14 . 
   In this work vehicle  1 , in order to improve the traveling stability, the working stability, etc. by lowering the gravity center Q of the traveling body  4 , the engine  13  is disposed on the traveling body  4 . Further, in order to dispose the swivel base  6  at a lowest possible position in spite of the engine  13  being mounted on the traveling body  4 , the engine  14  is mounted at the rear portion of the traveling body  4 . Further, by disposing the power transmission mechanism  14  forwardly of the engine  13 , the vertical dimension of the traveling body  4  under the swivel base  6  is reduced advantageously. 
   A distance L 1  measured from the center  5 S of the swivel shaft  5  and the rear end of the upper structure  11  is set to be within a distance L 2  measured from the center  5 S of the swivel shaft  5  and the rear ends of the rear wheels  3  or at least within a distance L 3  measured from the center  5 S of the swivel shaft  5  and the rear end of the traveling body  4 . With this, when the upper structure  11  is swiveled, this will not hit an object which may be present rearwardly. 
   As shown in  FIGS. 8 ,  12 ,  14 ,  16  and  17 , the swivel joint (swivel shaft)  5  includes a cylindrical member  141  fixed to the vehicle frame  21  of the traveling body  4  via a bracket  140 , and a center shaft  143  rotatably mounted inside the cylindrical portion  141  and non-rotatably attached to the swivel base  6  via a stopper plate  142 . At an upper portion of this center shaft  143 , there is provided an oil passage connecting annular member  144  connected to an actuator. Downwardly of the cylindrical member  141  and the center shaft  143 , there is provided (electric) current-carrying means  145 . 
   The cylindrical member  141  has a large surface area. Hence, various pipes are connected thereto with appropriate peripheral and axial spaces therebetween. More particularly, from the top to the bottom of the cylindrical member  141 , this member  141  defines a pilot connection opening  141   j , a hydrostatic transmission  26  connection opening  141   e , an oil pressure signal connection opening  141   n , a brake connection opening  141   h , a power steering cylinder  71  left connection opening  141   c , a power steering cylinder  71  right connection opening  141   d , a dozer actuator cylinder  78  elevating connection opening  141   f , a dozer actuator cylinder  78  lowering connection opening  141   b , a swivel motor  15  right swiveling connection opening  141   i , a swivel motor  15  left swiveling connection opening  141   g , an auxiliary hydraulic motor connection opening  141   k , a main connection opening  141   m , a drain  141   t , etc. 
   Inside the center shaft  143 , there is formed an oil passage communicating the respective connection openings of the cylindrical member  141  to the oil passage connecting annular member  144  via radial oil passages and axial oil passages. Hence, to the oil passage connecting annular member  144 , there are connected pipes communicating with these oil passages. Incidentally, the center shaft  143  and the oil passage connecting annular member  144  may be formed integrally. 
   Although the oil passage connecting annular member  144  may define various connection openings to be connected with pipes, this will require an area for defining these connection openings as large as that of the cylindrical member  141 . For this reason, in the instant embodiment, the pipes are integrally welded in the form of a multi-directional piping arrangement on the surface of the oil passage connecting annular member  144 . 
   This oil passage connecting annular member  144  projects upward from the swivel bearing  36  into the swivel base  6 . In particular, the swivel base  6  includes right and left raised ribs  35 , so it is difficult for the multi-directional piping arrangement  146  to project from the oil passage connecting annular member  144  in the right/left directions. For this reason, the piping arrangement  146  is bent in the middle thereof to be oriented in the fore-aft direction. 
   The piping arrangement  146  is disposed lower than the top face of the raised ribs  35  and the swivel base  6  defines an opening  6   a  for introducing a hose connecting between the piping arrangement  146  and the upper structure  11 . 
   The center shaft  143  defines a through hole  147  along the axis thereof, into which a harness  148  is inserted. The bottom face of the center shaft  143  defines an engaging recess  150  for engagement with a coupling  149 . 
   To the bottom of the cylindrical member  141 , there is detachably attached a joint cover  151  and a case member  152  is attached to an upper portion of this joint over  151  and the current-carrying means  145  is disposed between the case member and the joint cover  151 . 
   To a fixed side of the joint cover  151  or of the case member  152 , there is fixed a stationary current-carrying member  153  such as a brush, which comes into sliding contact with a movable current-carrying member  154  for establishing electric connection therewith. 
   The movable current-carrying member  154  is disposed under a rotary shaft  155  coaxial with the center shaft  143  and rotatably supported to the case member  152 . And, the coupling  149  is fitted to an upper portion of this rotary shaft  155  projecting from the case member  152  and this coupling  149  is inserted into the engaging recess  150  to be engaged with the center shaft  143 , whereby the rotary shaft  155  is rotated together with the center shaft  143 . 
   The harness  148  has its one end connected to an electric controller mounted on the swivel base  6  and the other end inserted into the rotary shaft  155  to be connected with the movable current-carrying member  154 , whereby electric current supply to the engine  13  and various electromagnetic valves mounted on the traveling body  4  is controlled via the stationary current-carrying member  153 . 
   The current-carrying means  145  is used mainly for carrying electric current for control signals, but may be used for supplying electric power for driving motors. 
   On the swivel base  6 , an implement support unit  37  is provided erect at a front portion and a rear wall portion  34  is provided erect at a rear portion of the base. And, the right and left raised ribs  35  provided erect at the intermediate portion of the base  6  connect the implement support unit  37  with the rear wall portion  34 , whereby the entire swivel base  6  is formed as a strong three-dimensional structure. 
   Referring to  FIG. 1  and  FIGS. 4–7 , there is provided a driver&#39;s seat mounting frame  51  which extends rearward from the upper portion of the rear wall portion  34  of the swivel base  6  and projects over and above the engine  13 . To form this driver&#39;s seat mounting frame  51 , a pair of right and left transverse pipe members  51 B are secured to an attaching plate  51 A secured to the top face of the rear wall portion  34  and vertical pipe members  51 C project rearward from the right and left transverse members  51 B and the right and left vertical members  51 C are connected via a plurality of connecting members  51 D. Then, this driver&#39;s seat mounting frame  51  mounts the driver&#39;s seat  7  at a front portion thereof and also mounts at rear portions thereof the hydraulic control valve  56  of the controller  55 , an electric generator  159  having an auxiliary hydraulic motor  158  and a battery  160 . 
   At an upper portion of the implement support unit  37  of the swivel base  6 , there are provided a pair of right and left support members  38 . This support member  58  includes a hooked-shaped member  58 A and a horizontal transverse pipe member  58 B projecting from the member  58 A. The hooked members  58 A are bolt-fixed to the implement support unit  37  and the transverse members  58 B form a pair of right and left ROPS support portions. 
   The right and left transverse members  51 B of the driver&#39;s seat mounting frame  51  also constitute the ROPS support portions. To the transverse member  51 B and the transverse member  58 B disposed one in front of the other, front and rear struts  52 F,  52 R of the right and left ROPS  53  are connected and supported. 
   Referring more particularly to the ROPS  53 , its portion from the rear strut  52 R to the upper portion  52 U is formed by bending a single pipe member in the substantially U-shape and the upper portion  52 U and the upper end of the front strut  52 F are connected to each other. Then, these right and left ROPS  53  are connected via a plurality of connecting rods  60  and a canopy  90  is attached to the upper portion  52 U for sun beam shading. 
   To the bottom ends of the front and rear struts  52 F,  52 R, connecting members  59 F,  59 R are fixedly attached. Each of these connecting members  59 F,  59 R includes a connecting portion in the form of a pipe or a solid bar and an elbow portion for disposing this connecting portion to the strut  52  perpendicularly. As the connecting portions are inserted into the transverse members  51 B,  58 B and these are fixed by means of bolts extending through both the connecting portions and the members, the ROPS  63  may be attached to the swivel base  6 . 
   Incidentally, the connecting portions may be connected with the transverse members  51 B,  58 B through engagement therewith, or both of these may be formed of plate members, angle members, etc. 
   Each of the right and left rear struts  52 R is bent in an L-like shape, so that the strut extends from the rear wall portion  34  of the swivel base  6  to a position rearward and upward of the driver&#39;s seat  7  and then extends upward from its intermediate portion, whereby this strut projects upwardly of the engine  13  together with the driver&#39;s seat mounting frame  51 . 
   Accordingly, the driver&#39;s seat mounting frame  51  and the operator&#39;s seat  7  are disposed at a position higher than the engine  13 , so that the swivel base  6  when being swiveled, can pass above the engine  13 , that is, pass above the raised portion  4 B which forms the highest portion of the traveling body  4 . 
   With the above-described arrangements of mounting the engine  13  on the rear portion of the traveling body  4  and disposing the driver&#39;s seat  7  at the position projecting rearwardly and upwardly from the swivel base  6 , on the swivel base  6 , the driver&#39;s seat  7  is disposed on the rear portion thereof and also the steering unit  8  is disposed on the front portion thereof. Consequently, the weight of the upper structure  11  is reduced significantly and its fore-and-aft dimension may be the necessity minimum dimension. 
   And, the area of the swivel base  6  forwardly of the operator&#39;s seat  7  may be efficiently utilized as a space reserved for the driver and the swivel base  6  may be disposed within a limited area and at a low position, so that the entire work vehicle  1  may be formed compact in the fore-and-aft direction, the right-and-left direction and the vertical direction as well. 
   The driver&#39;s seat mounting frame  51  supports right and left lever manipulating means  55 L,  55 R of manipulating units  55  disposed on the right and left sides of the operator&#39;s seat  7  for manipulating the ground-work implement. These right and left lever manipulating units  55 L,  55 R are for manipulating a boom cylinder  43 , an arm cylinder  45 , an implement cylinder  47  etc. of the ground-work implement  9  to be described later and the swivel motor  15 , etc. 
   Further on the right and left side of the driver&#39;s seat  7 , there are disposed a manipulating lever  181  for the swing cylinder  41  of the ground-work implement  9 , a manipulating lever  182  for a tilt cylinder  184  of the implement  46 , and a manipulating lever  183  for the dozer actuating cylinders  78 . There are also provided other components such as a hand accelerator lever  187  for operating a governor of the engine  13  and traveling lock levers  188  for operating the traveling lock valve  178 . The traveling lock levers  188  are disposed on the right and left sides of the driver&#39;s seat  7 . 
   Rearwardly of the driver&#39;s seat mounting frame  51  and on the right and left sides of the hydraulic control valve  56 , there are disposed remote control valves for the swing, tilt and dozers to be manipulated by the manipulating levers  181 ,  182 ,  183 , these valves being connected with the respective manipulating levers  181 ,  182 ,  183  via a link, a rod, a cable, etc. 
   For allowing the high-speed vehicle run on the road, the steering unit  8  includes the steering wheel  73  and a steering controller  73 A of the steering wheel  73  and other associated components are attached to a support member  38  mounted erect on the swivel base  6  and rearwardly of the implement support unit  37 , so that these components may be mounted on the swivel base  6  as an assembly. 
   More particularly, as shown in  FIGS. 18 through 20 , in addition to the steering controller  73 A, the support member  38  pivotally supports also a change-speed pedal  94  for operating the hydrostatic transmission  26  for change-speed, which pedal  94  is disposed near a position where the driver&#39;s right foot is to be placed, and pivotally supports a brake pedal  91  in its vicinity. In addition, there are attached a master cylinder  101  and an oil tank  102  for operating the brake mechanism A as well as such other components as a damper  103  for the change-speed pedal  94  and a remote control valve  104  for the HST. 
   Along a handle post  73 B of the steering wheel  73 , there is disposed a shuttle lever  105  for operating a forward/reverse switch valve  174 . 
   The swivel base  6  mounts, at its front portion, the implement support unit  37  which supports the ground-work implement  9  with allowing the implement  9  to be pivoted to the right and left above the swivel base  6 . While the steering wheel  73  of the steering unit  8  is disposed at the substantially right-and-left center of the front portion (may be offset to the left) of the swivel base  6 , the implement support unit  37  is disposed with offset to the right so as to provide better visibility of the operating condition of the ground-work implement  9 . 
   As shown in  FIGS. 1–4  and  18 , the implement support unit  37  is disposed erect at the front portion of the swivel base  6  so as to connect the front ends of the right and left raised ribs  35  as well as to cover the front side of the steering unit  8  and supports a swing shaft  39  provided as a vertical shaft. This swing shaft  39  pivotally supports a swing member  40  which is pivoted by a swing cylinder  41 . The swing member  40  pivotally supports a boom  42  and a boom cylinder  43  for lifting up/down this boom  42  via horizontal shafts  48 A,  48 B. 
   The swing member  40  is pivotally supported to an upper portion of the implement support unit  37  and a rotary shaft  163  as a vertical shaft is pivotally supported to a lower portion of the implement support unit  37 . To this rotary shaft  163 , an upper arm  164  and a lower arm  165  are secured, with the upper arm  164  being connected to the swing member  40  via a link  166  and the lower arm  165  being connected to the swing cylinder  41 , so as to act as a start-up coupling means for transmitting operational force of the lower swing cylinder  41  to the upper swing member  40 . 
   The portion of the swing member  40  pivotally supporting the lower boom  42  projects radially from the outer periphery (outer peripheral swiveling path) of the swivel base  6 . The portion of the swing member  40  pivotally supporting the base of the upper boom cylinder  43  is located substantially above the swing shaft  39  and within the outer periphery of the swivel base  6 . 
   The implement support unit  37  is disposed so as to be substantially confined within the outer periphery of the swivel base  6  and the unit  37  has a height so set as to allow the boom  42  and the boom cylinder  43  to pass above the highest position of the traveling body  4 . Hence, even when the boom  42  is swiveled rearward, this will not come into contact with the front portion of the hood cover  80  as long as the boom  42  assumes an upper posture than the horizontal. 
   That is to say, when the ground-work implement  9  on the swivel base  6  is swiveled, this will not collide the traveling body  4 . Therefore, the vehicle can carry out a ground work with the swivel base  6  assuming the backward posture. Hence, the ground work such as an excavating work is possible over the entire movable range of the traveling body  4 . 
   The ground-work implement  9  includes, at the leading end of the boom  42 , an arm  44  which is vertically pivotable by an arm cylinder  45 . And, at the leading end of this arm, there is provided an implement (bucket or the like)  46  which can be pivoted up and down by the implement cylinder  47 . 
   The implement  46  has its right-to-left center portion supported to be pivotable about a fore-and-aft shaft and has right and left side portions vertically pivotable by the tilt cylinder  184 . 
     FIGS. 21 and 22  show the hydraulic circuit of the wheeled work vehicle  1 . This circuit is divided across the swivel joint (shaft)  5  between a section for the traveling body  4  and a further section for the upper structure  11 . 
   The power of the engine  13  drives the pump  81  of the transmission  26  and drives also the charge pump  109 . This power is capable of driving also the hydraulic pump  85  via the reduction gear set  107  and the hydraulic clutch  110 . 
   The transmission  26  includes a shuttle valve  170  and a high/low speed switchover valve  171  which is operable by an electromagnetic valve  169  to operate a swash-plate control actuator  172  of the motor  82 , thereby to selectively realize a high-speed condition and a low-speed condition. 
   The pump  81  is connected to a speed actuator  173  for switching over forward/reverse drive modes and the speeds thereof. This speed actuator  176  is switched over between the forward drive mode and the reverse drive mode by a forward/reverse selector valve  174  and can be controlled by a remote control valve  104  operable by the change-speed pedal  94 . 
   The work oil from the charge pump  109  flows through the traveling lock valve  175  to reach the remote control valve  104  and then flows from this remote control valve  104  to either the forward driving side or the reverse driving side of the forward/reverse selector valve  174 . Hence, according to an amount of the driver&#39;s stepping operation on the change-speed pedal  94 , the speed control valve  176  is operated correspondingly to control the speed actuator  173 . 
   The numeral  177  denotes the differential lock mechanism, which is operable to check or not check the work oil from the charge pump  109  by a differential lock selector valve  178 , thereby to selectively provide a differential locked condition and a differential released condition. 
   The work oil from the hydraulic pump  85  is fed to the hydraulic control valve  56  comprising an assembly of a plurality of valve elements  56   a – 56   g . Then, the oil is supplied through the respective valve elements  56   a – 56   g  of the hydraulic control valve  56  to the respective actuators. 
   The left lever manipulating means  55 L of the manipulating unit  55  includes remote control valves for the arm and for swiveling for operating the arm cylinder  45  via the arm valve element  56   e  for a scraping or dumping operation and for operating the swivel motor  15  via the swivel valve element  56   f  for right or left swiveling. 
   The right lever manipulating means  55 R includes remote control valves for the implement and the boom for operating the implement cylinder  47  via the implement valve element  56   c  for a tilting/dumping operation and operating the boom cylinder  43  via the boom valve element  56   d  for elevating/lowering movement. 
   Adjacent the left and right lever manipulating means  55 L,  55 R (or adjacent the steering unit  8 ), the three manipulating levers  181 ,  182 ,  183  are arranged. The manipulating lever  181  is for operating the remote control valve for the swing, i.e. for operating the swing cylinder  41  for right or left pivotal movement via the swing valve element  56   b . The manipulating lever  182  is for operating the remote control valve for the tilt, i.e. for operating the tilt cylinder  184  via the tilt valve element  56   a . The manipulating lever  183  is for operating the remote control valve for the dozers, i.e. operating the dozer operating cylinder  78  for upward/downward movement via the dozer valve element  56   g.    
   The hydraulic pump  85  is connected to an auxiliary pump  185 . The work oil of this auxiliary pump  185  is fed to an auxiliary hydraulic motor  158  and then via the steering controller  73 A to the steering hydraulic cylinder  71 . 
   In summary, the transmission  26 , the swivel motor  15 , the pumps  109 ,  85 ,  185 , the steering hydraulic cylinder  71 , the dozer operating cylinder  78 , the traveling lock valve  175 , the selector valves  54 , etc. are all mounted on the traveling body  4 . Whereas, the manipulating unit  55 , the change-speed pedal  94 , the steering controller  73 A, the three manipulating levers  181 ,  182 ,  183 , the auxiliary hydraulic motor  158 , the hydraulic control valve  56 , etc. are mounted on the upper structure  11 . And, the work oil can be supplied/discharged vertically via the swivel joint  5 . Further, via the current-carrying means  145  provided at the swivel joint  5 , control signals for the electromagnetic valves for controlling the transmission  26  and the other electromagnetic valves and the other electric devices can be transmitted from the upper structure  11  to the traveling body  4 . 
   The forward/reverse switch valve  174 , the traveling lock valve  175 , the differential lock switch valve  178 , the electromagnetic control valve  169 , etc. are mounted as the selector valves  54  at the front portion of the traveling body  4  and constitute the hydraulic system together with the pumps  109 ,  85 ,  185 , etc. 
   Although it is preferred that the wheeled work vehicle  1  include all of the respective components described above, it is also possible for the vehicle to include some of them selectively or in different combinations. 
   For instance, the traveling body  4  having the front and rear wheels  2 ,  3  may mount the traveling drive unit  12  and the dozers  10  and the swivel base  6  may be disposed at a position lower than the uppermost position of the traveling body  4 , thereby to allow the full-angle swiveling movement of the base  6 . And, on this swivel base  6 , the upper structure  11  having the driver&#39;s seat  7  and the steering unit  8  and the ground-work implement  9  may be mounted. With this basic construction, according to the present invention, the vehicle may include at least one of the following features (a) through (g). 
   (a) The upper structure  11  and the ground-work implement  9  mounted on the swivel base  6  are adapted to be able to pass above the engine  13 . 
   (b) In the traveling body  4 , its portion downwardly of the swivel base  6  is formed as the flat portion  4 A and its portion rearwardly of the swivel base  6  is formed as the raised portion  4 B. 
   (c) The engine  13  is disposed at the rear portion of the traveling body  4  and the swivel base  6  is disposed at a position lower than the upper end of the engine  13 . 
   (d) Of the swivel bearing  36  and the swivel base  6  at least the swivel bearing  36  is disposed between the front and rear wheels  2 ,  3  and at a position lower than the upper end of at least one of them. 
   (e) The implement support unit  37  is disposed substantially within the outer periphery of the swivel base  6 . 
   (f) The driver&#39;s seat  7  is disposed to project rearward from the swivel base  6 . 
   (g) The base portion of the ground-work implement  9  supported by the implement support unit  37  is disposed at a position hither than the front and rear wheels  2 ,  3  and the engine  13 . 
   These features may be used in various combinations also when the basic construction of the wheeled work vehicle  1  is added with the further feature of e.g. setting the total weight of at least the swivel base  6 , the driver&#39;s seat  7 , and the steering unit  8  among the swivel base  6 , the driver&#39;s seat  7 , the steering unit  8  and the ground-work implement  9  to be less than the total weight of the traveling body  4  including the front and rear wheels,  2 ,  3  or the still further feature of limiting the distance L 1  from the swivel shaft  5  to the rear end of the upper structure  11  within the distance L 2  from the swivel shaft  5  and the rear wheel  3 . 
   The above-described wheeled work vehicle  1  is suitable for effecting such works as a grading operation on an inclined ground or a limited space for which the skid steering loader is generally not suited. Although this vehicle can effect such work as collecting earth while moving about, the vehicle is good at such operation of collecting earth by the hydraulic power while the vehicle is parked still on the ground. And, with exchange of implements  46  having different widths, this single vehicle can effect both a transporting operation and a ditch digging operation for a depth less than 1.8 m such as for laying a wire under the ground. 
   That is to say, the grading operations using machinery are divided roughly into the transporting operation and the grading operation. And, this wheeled work vehicle  1  can effect with particularly high efficiency the grading operation which is a non-transporting, earth moving operation, such as for forming a slope or undulation on the ground surface or leveling the ground surface, or collecting the earth, back-filling a ditch or a hole, etc. 
   The front/rear, right/left and upper/lower positional relations among the respective components employed in the foregoing embodiment are best as shown in  FIGS. 1–22 . However, the invention is not limited to the foregoing embodiment, but may be varied in many ways by modifying these components or combinations thereof. 
   For instance, in place of the four-column type ROPS  53  employed in the foregoing embodiment, a two-column type ROPS or a cabin unit may be mounted on the vehicle. The manipulating unit  55  may be disposed adjacent the steering wheel  73 . Further, the drive wheels may be replaced by crawlers, while providing the driven wheels as wheels. 
   In these manners, the invention may be embodied in any other manner as described above. Further changes or modifications will be apparent for those skilled in the art from the foregoing disclosure within the scope of the invention defined in the appended claims.