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BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a loader work machine. The term “loader work machine” as used herein refers generically to a group of loading/unloading vehicles for use in agricultural works, civil engineering works, etc. some non-limiting examples of which include a tractor mount type loader formed by mounting a front loader and/or a backhoe to a tractor, a self-propelled loader (wheeled loader, self-propelled backhoe, a power shovel, etc.) 
   2. Description of the Related Art 
   There is known a loader work machine in which an accumulator for absorbing shock occurring during a vertical pivotal movement of a work device (e.g. a front loader) connected to a self-propelled vehicle body is connected to a hydraulic circuit (see e.g. Japanese Utility Model Application “Kokai” No. 56-171868). This accumulator is disposed adjacent a boom cylinder forwardly, rearwardly or upwardly, etc. of a connecting pipe interconnecting right and left boom members. 
   However, when the work device is connected to the self-propelling vehicle body, the accumulator is attached to a relative high position of the loader work machine. Hence, due to this accumulator, the front visibility from a driver&#39;s seat is deteriorated. Moreover, the attachment of the accumulator to the connecting pipe deteriorates not only the front visibility, but the aesthetic appearance. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is to provide a loader work machine which overcomes the above-described drawback. 
   For accomplishing the above-noted object, a loader work machine, according to the present invention, comprises: 
   a self-propelled machine body; 
   a work device having a boom, a boom cylinder, and a side frame for vertically pivotally supporting base portions of the boom and the boom cylinder; 
   a frame unit for attaching the work device to the self-propelled machine body, the frame unit including:
         a support platform projecting laterally outward from the self-propelled machine body, and   a main frame mounted erect on the support platform for supporting and connecting a lower portion of the side frame; and       

   an accumulator connected to the boom cylinder for absorbing shock occurring during a vertical pivotal movement of the work device; 
   wherein said accumulator is attached to said frame unit. 
   With the above-described construction, the accumulator is attached to a lower position than the conventional construction. Hence, with elimination of blocking of the front view from the driver&#39;s seat toward the work device (e.g. a front loader), the front visibility can be improved and the aesthetic appearance of the work machine can be improved as well. 
   According to one preferred embodiment, said accumulator is stored within a lower portion of said frame unit. For instance, this accumulator can be stored inside the support platform which is formed like a cylinder. 
   According to one preferred embodiment, said main frame includes a selector valve operable to switch over the accumulator between a use condition and a non-use condition, with the selector valve being operable from a driver&#39;s seat mounted on the self-propelled machine body. With this construction, it is possible to shorten a hydraulic piping between the accumulator and the selector valve. Further, the switchover operation of the selector valve becomes more convenient. 
   According to one preferred embodiment, said support platform is formed like a cylindrical platform structure which accommodates therein a selector valve operable to switch over the accumulator between a use condition and a non-use condition. With this construction, not only the accumulator, but also the selector valve is accommodated within the support platform. Therefore, the blocking of the front view for the driver can be further prevented and the aesthetic appearance of the machine can be further improved. 
   Further and other features and advantages of the invention will become apparent upon reading the following detailed description of the preferred embodiments thereof with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an overall side view of a tractor mount type loader implementing the present invention, 
       FIG. 2  is a partially enlarged side view of an accumulator attaching portion, 
       FIG. 3  is a plan view of  FIG. 2 , 
       FIG. 4  is a front view of  FIG. 2 , 
       FIG. 5  is an enlarged section of a support platform portion accommodating an accumulator therein, and 
       FIG. 6  is an enlarged section of a support platform relating to a further embodiment of the invention which accommodates a selector valve in addition to the accumulator. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Next, with reference to the accompanying drawings, respective preferred embodiments of the present invention will be described in details based on a tractor mount type loader as an example of a loader work machine relating to the present invention. 
   First Embodiment 
   In  FIG. 1 , there is shown at  1  a tractor mount type loader comprising a tractor (loading/unloading vehicle)  2  as a self-propelled machine body and a front loader  3  as a work device attached to a front portion of the tractor  2 . 
   The tractor  2  includes a pair of right and left front wheels  4 , a pair of right and left rear wheels  5 , and a hood  6  mounted at a front portion of the tractor for covering an engine, a radiator, etc. 
   The front loader  3  includes, as principal components thereof, attaching frames  7 , boom members  8  and an implement  9  such as a bucket. The attaching frame  7  includes a cylindrical support platform  10 , a main frame  11 , and a side frame  12 . And, the pairs of these components are disposed on the right and left sides of the tractor  2 , respectively. 
   As shown in  FIGS. 1-4 , the tractor  2  includes a front axle frame  2 A, a flywheel housing  2 B and a connecting frame  2 C interconnecting the frames  2 A,  2 B along the fore and aft direction. 
   The connecting frame  2 C comprises a pair of plate-like members having front half portions thereof fastened to the right and left side faces of the front axle flame  2 A by a plurality of bolts and having rear half portions thereof fastened to the right and left side faces of the flywheel housing  2 B by a plurality of bolts. To the front portion of the flywheel housing  2 B, the engine (not shown) is connected and to the rear portion thereof, a clutch housing, a transmission case and a rear wheel differential device are connected in the mentioned order. 
   The cylindrical support platform  10  comprises a metal pipe member such as a cylindrical steel pipe. This support platform  10  has its right/left inner end inserted into a circular hole  2 D formed at a rear portion of the connecting frame  2 C and fixedly welded about this circular hole  2 D. With this, right/left outer ends of the support platform  10  project outward in the right/left direction from the tractor  2 . And, on the right and left outer ends of the support platform  10 , the main frames  1  are attached to project upward therefrom. To this end, each main frame  11  forms, at a lower end thereof, a circular hole  11 A, in which the right/left outer end of the support platform  10  is inserted and the support platform  10  is fixedly welded around this circular hole  11 A. 
   Referring more particular to the main frame  11 , as shown in  FIG. 2 , at an upper portion thereof, there is integrally formed a cylindrical boss portion  11 B forming a pin hole having a right/left axis and, at a front portion of a vertically intermediate portion thereof, there is integrally formed a receiving portion  11 C having an upwardly open arcuate receiving recess. This main frame  11  is integrally formed as a single plate (thick plate) made of cast steel. In the opposed lateral plate face portions (or one lateral plate face portion), there are formed a plurality of reinforcing ribs  11 D arranged to intersect with each other in the vertical and fore-and-aft directions, with forming recesses  11 E between adjacent reinforcing ribs  11 D for achieving weight reduction. 
   The main frames  11  described above are attached to the front opposed lateral faces of the tractor  2  via the support platforms  10  and the connecting frames  2 C so as to detachably connect the side frames  12  of the front loader  3  to the front portion of the tractor  2 . 
   The side frames  12  are attached to rear ends of the pair of right and left boom members  8  of the front loader  3  so as to detachably connect the front loader  3  to the front portion of the tractor  2  with using the main frames  11 . 
   To the above end, to the lower end of each side frame  12 , there is integrally fixed an engaging pin  13  engageable with the receiving portion  11 C of the main frame  11 . Further, at a rear portion of a vertically intermediate portion of the side frame  12 , there is integrally provided a cylindrical boss portion  12 A having a pin hole corresponding to the boss portion  11 B of the main frame  11 . 
   Then, with engaging the receiving portions  11 C of the main frames  11  to the engaging pins  13  of the side frames  12 , the opposed boss portions  11 B,  12 A will be placed in registry with each other and the connecting pins  14  will be inserted therethrough, whereby the front loader  3  can be connected to the tractor  2 . Further, by removing the connecting pins  14 , the front loader  3  becomes detachable from the tractor  2 . 
   The boom member  8 , as shown in  FIG. 1 , is bent at a longitudinally intermediate portion thereof, so that this entire member  3  presents a mountain-like shape convexed upward. Further, the boom member  8  has a progressively larger height from the fore and rear end portions thereof toward the longitudinally center portion thereof. And, this entire boom member  8  is formed like a substantially angular tubular structure made of a metal plate member such as a steel plate. And, the pair of the boom members  8  are provided on the right and left sides of the hood  6 . The front portions of the right and left boom members  8  are interconnected via a connecting pipe  15 . 
   Each of the right and left boom members  8  is pivotally connected, at a proximal end (rear end) end thereof, via a pin  16  to the upper portion of the corresponding side frame  12  to be vertically pivotal about a right/left axis. 
   Further, from the longitudinal intermediate portion of each right/left boom member  8  to a vertically intermediate portion of each right/left side frame  12 , there is disposed a boom cylinder  17  comprised of a double acting type hydraulic cylinder. In operation, in association with extension/contraction of these right and left boom cylinders  17 , the right and left boom members  8  can be vertically pivoted. 
   To a rear side lower portion of the implement  9 , leading ends (front ends) of the respective boom members  8  are pivotally connected via pins  18 . And, between the rear face of the implement  9  and the vicinity of the leading end of each right/left boom member  8 , opposed ends of a two-foldable extension/contraction link  19  are connected via pins  20 ,  21 . Further, between an upper face of the longitudinally intermediate portion of each right/left boom member  8  and a mid connecting point of the two-foldable extension/contraction link  19 , there is disposed a bucket cylinder  22  comprised of a double acting type hydraulic cylinder. Then, in association with extension/contraction of the bucket cylinders  22 , the implement  9  can be pivoted (for a rollback or dumping operation). 
   Along the lower face on the leading end side of the boom member  8 , a stand  23  is attached. This stand  23  is used for supporting the boom member  8  to allow this member  8  to stand alone with the implement  9  being placed on the ground surface, when the front loader  3  is to be detached from the tractor  2 . Incidentally, this stand  23  can be stored and held along the lower face of the leading end side of the boom member  8 . 
   To the hydraulic circuit of the boom cylinder  17 , there is connected an accumulator  24 . This accumulator  24  is disposed on the side of the main frame  11 . In the present embodiment, there is disclosed an exemplary construction wherein the accumulator  24  is stored within the support platform  10  of the main frame  11 . As the support platforms  10  are provided on the right and left sides of the tractor  2 , the accumulators  24  are accommodated similarly within the right and left support platforms  10 . In the present embodiment, one accumulator  24  is connected respectively to a boom elevating side oil passage and a boom lowering side oil passage of the hydraulic circuitry (not shown) of the boom cylinder  17 . 
   The accumulator  24 , as shown in  FIG. 5 , consists essentially of a cylindrical body  24 A having a slightly smaller outer diameter than the inner diameter of the cylindrical support platform  10  and a lid member  24 B air-tightly fastened to the body  24 A. And, this accumulator  24  is accommodated within the support platform  10  via a cushion member  25  such as a rubber sheet, and an attaching bolt  26  provided at an end of the body  24 A is inserted through an attaching plate  27  affixed to right/left inner side of the cylindrical platform  10  and fastened thereto by a nut  28 . 
   As shown also in  FIG. 5 , each accumulator  24  accommodated within the right/left support platform  10  includes a pipe connecting member  29  at an end on the right/left outer side of the cylindrical support platform  10 , and to this pipe connecting member  29 , a hydraulic pipe  31  is connected. This hydraulic pipe  31  is drawn out through an open end on the right/left outer side of the support platform  10 , and then connected to a selector valve  30  attached to a side face of the main frame  11 , which side face is exemplified as a position operable for switchover operation from a driver&#39;s set  2 F of the tractor  2 . The selector valve  30  is connected via the hydraulic pipe  31  to a predetermined connecting port of a control valve  32 . This control valve  32 , as shown in  FIGS. 2-4 , is attached to the right side face of the clutch housing  2 E constituting a part of the vehicle body of the tractor  2 . To the selector valve  32 , there is pivotally attached a handle shaft  33 . Then, as this handle shaft  33  is pivoted with a convenient tool (not shown) such as a spanner, the selector valve  30  switches over the oil passage to an open condition or to a closed condition. With this, the accumulator  24  is switched over between a use condition and a non-use condition. The above-described operational tool can be permanently attached to the handle shaft  33  or detachably attached thereto. 
   In the foregoing embodiment, the selector valve  30  is provided at the side face of the main frame  11  as an example of a position switchably operable from the driver&#39;s seat  2 F of the tractor  2 . Instead, the valve  30  can be provided at any other position, e.g. to the rear face of the main frame  11  or can be attached directly or indirectly via an appropriate attaching bracket to a portion of the vehicle body of the tractor  2 . In short, this selector valve  30  should be connected to a mid portion of the hydraulic pipe  31  connecting the accumulator  24  and the control valve  32 , and be disposed at a position conveniently operable for switchover from the driver&#39;s seat  2 F of the tractor  2 . 
   Incidentally, the selector valve  30  may be disposed adjacent the accumulator  24 . For instance, as shown in  FIG. 6 , the selector valve  30  may be accommodated within the support platform  10  together with the accumulator  24 . In this case, the pivoting operation of the handle shaft  33  is to be effected by inserting the tool from the open end on the right/left outer side of the support platform  10 . Incidentally, at this open end on the right/left outer side of the support platform  10 , there is detachably attached a lid member  34  made of rubber or plastics for preventing intrusion of dust or the like. This lid member  34  will be detached when the pivoting operation of the handle shaft  33  is to be effected. 
   To the inner face of the main frame  11  disposed on the right side of the tractor  2 , there is attached, via a support bracket  35 , a hydraulic pipe connecting terminal tool  36 . This hydraulic pipe connecting terminal tool  36  is connected via a hydraulic pipe  37  to the control valve  32 . The control valve  32  is connected to a hydraulic pump and an oil tank (not shown) mounted on the tractor  2 . The hydraulic pipe connecting terminal tool  36  is used for feeding/discharging working oil to/from the boom cylinders  17  and the bucket cylinders  22  of the front loader  3 . The hydraulic pipe (not shown) to the boom cylinders  17  and the hydraulic pipe (not shown) to the bucket cylinders  22  are arranged along the boom members  8  of the front loader  3 . And, to terminal ends of these hydraulic pipes too, there are provided hydraulic pipe connecting terminal tools (not shown) which are connectable to and detachable from the terminal tool  36  in the male-female arrangement. These terminal tools will be connected or detached when the front load  3  is mounted to or dismounted from the tractor  2 . 
   Next, the operations of this embodiment having the above-described construction will be described. 
   As shown in  FIG. 1 , when a work is to be effected by the front loader  3  with this loader  3  being mounted to the tractor  2 , by selective operations of the selector valves  30 , there are three types of operations selectable, i.e. one rendering both of the right and left accumulators  24  usable, another rendering both unusable and still another rendering one of them usable, rendering the other unusable. 
   First, the case of rendering both of the right and left accumulators  24  usable is a case where, during a work with vertically pivoting the boom members  8  by the boom cylinders  17 , sudden change in the loads due to some cause is expected or it is necessary to avoid generation of such shock per se. In such case, the work will be carried out with opening the right and left selector valves  30 . With this, even if there occurs sudden surge in the oil pressure in the hydraulic pipes connected to the boom cylinders  17 , this can be absorbed and relieved by the accumulators  24 , thus effectively preventing transmission of significant shock to the driver and to the implement  9  such as the bucket. As a result, it is possible to avoid fall of the load as well as damage to the boom members  8  and the implement  9 . Moreover, it is possible to avoid burst of the hydraulic pipes or oil leaks therefrom. 
   The case of rendering both the right and left accumulators  24  unusable is a case where the boom cylinders  17  need to be operated with maximum hydraulic forces. In such case, the work will be effected with closing the right and left selector valves  30 . 
   Further, in the case of effecting work with rendering only the elevating operation side accumulator  24  for the boom cylinder  17  usable and rendering the lowering operation side accumulator  24  unusable or in the converse case, the work will be effected with the corresponding one of the right and left selector valves  30  open and the other closed. 
   According to the present invention described above, as the accumulator  24  is accommodated within the support platform  10 , during a work of the front loader  3 , the accumulator  24  does not impair the front view of the driver and the aesthetic appearance is improved also. Further, there is no increase in the weight of the boom members  8 . Incidentally, the accumulator  24  need not be accommodated within the support platform  10 , but may be provided on the side of the main frame  11  outside the support platform  10 , and in such case too, no deterioration in the driver&#39;s front view will occur and no weight increase in the boom member  8  will occur, either. 
   Second Embodiment 
     FIG. 6  shows a loader work machine according to a second embodiment of the present invention. 
   In this embodiment, the selector valve  30  is accommodated within the support platform  10 . With this accommodation within the support platform  10 , piping layout can be facilitated and the appearance can be improved. 
   The rest of the construction is identical to the first embodiment. 
   Other Embodiments 
   The present invention is not limited to the foregoing embodiments. 
   For instance, both of the right and left accumulators  24  can be used only for either elevating or lowering operation of the boom cylinders  17 . Or, instead of providing the accumulators on the opposed right and left sides, one integral accumulator may be provided to be used for only either elevating or lowering side of the boom cylinders  17 . In this case, the accumulator  24  may be accommodated within only one of the right and left support platforms  10  or may be disposed outside the support platform  10  to be attached to a portion of the main frame  11  or a portion of the vehicle body of the tractor  2 . 
   Further, the disposing position of the selector valve  30  is not limited to the one described in the foregoing embodiment. The selector valve  30  may be disposed outside the support platform  10  at any appropriate position operable for switchover from the driver&#39;s seat  2 F. For instance, this selector valve  30  may be attached to a portion of the main frame  11 , so that the driver as being seated at the driver&#39;s seat  2 F can operate the valve without having to get off the vehicle body. 
   Incidentally, in the above case of disposing the selector valve  30  outside the support platform  10  to be attached to a portion of the main frame  11  or of the vehicle body, the two selector valves may both be disposed on one either side. This arrangement allows operation of the two selector valves on one side, thus further improving the operability.

Summary:
The invention provides a loader work machine with improved front visibility and improved aesthetic appearance. The loader work machine includes a self-propelled machine body, a work device having a boom, a boom cylinder, and a side frame for vertically pivotally supporting base portions of the boom and the boom cylinder, and a frame unit for attaching the work device to the self-propelled machine body. The frame unit has a support platform projecting laterally outward from the self-propelled machine body and a main frame mounted erect on the support platform for supporting and connecting a lower portion of the side frame. An accumulator is connected to the boom cylinder for absorbing shock occurring during a vertical pivotal movement of the work device and this accumulator is attached to the frame unit.