Patent Publication Number: US-10327383-B2

Title: Mid-mount mower with power transmission coupling

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 14/489,981, filed on Sep. 18, 2014, which claims priority to Japanese Patent Application Nos. 2013-272821 and 2014-158726, filed Dec. 27, 2013 and Aug. 4, 2014, respectively, the disclosures of which are hereby incorporated in their entireties by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a mid-mount mower having a mower unit disposed under a vehicle body between front wheels and rear wheels. 
     Description of the Related Art 
     In a mid-mount mower, a blade housing covering a rotary blade is connected to a lift link mechanism having a front link and a rear link attached to a vehicle body and spaced apart from each other in a vehicle front/rear direction. With this, the blade housing can be lifted up/down between a lowered working position and an elevated non-working position. When a maintenance/inspection of the mower unit or an operation other than a grass mowing operation is to carried out, the mower unit is dismounted from the vehicle body. It is very troublesome to carry out a connecting/disconnecting operation thereof in a limited space between the front wheels and the rear wheels. For this reason, it has been proposed to carry out at least some steps of the connecting/disconnecting operation in an automated manner. 
     For instance, in the case of a mid-mount mower disclosed in Japanese Unexamined Utility Model Application Publication No. 4-110428 (FIG. 1, FIG. 3) (Patent Document 1), in association with a forward traveling of the vehicle body, left and right front wheels roll over a blade housing, with utilizing a front wheel guide plate of this blade housing, to be positioned eventually at the body portion of a tractor. Then, in association with a final forward traveling, connection pins provided at free ends of a pair of left and right rear links are guided by openings formed at hook portions of a pair of left and right support stays provided in the blade housing and engaged into the deepest parts thereof. Then, lock arms provided in the respective support stays come into engagement with the connection pins with spring action, thus retaining the connection pins against inadvertent removal thereof, whereby the respective connection pins provided on the side of the vehicle body are connected to the respective support stays provided on the side of the mower. Thereafter, with establishment of connection between the front link and the front-side support stays, the connecting operation is completed. With the connecting arrangement disclosed in this Patent Document 1, connection of the front link needs to be carried out manually after connection of the rear link. After the connection pins of the pair of left and right rear links are guided by the openings of the hook portions of the blade housing and engaged into the deepest parts thereof, connection is established between the vehicle body and the blade housing. Simultaneously, engagement is established also between a clutch driving member of the vehicle body and a clutch driven member of the blade housing, thus enabling power transmission from the vehicle body to the blade housing. Under this condition, as lock arms provided in the respective support stays come into engagement with the connection pins by a spring action, thereby to retain the connection pins against inadvertent removal thereof, the respective pins of the vehicle body are connected to the respective support stays of the mower. Thereafter, with establishment of connection between the front links and the front-side support stays, the connecting operation is completed. In this way, in the case of the connecting arrangement disclosed in this Patent Document 1, connection between the vehicle body and the blade housing and connection for power transmission are effected simultaneously. 
     In Japanese Unexamined Patent Application Publication No. 10-339169 (FIG. 3, FIG. 4), there is disclosed an arrangement in which a hitch pin provided in a front link and a hitch pin provided in a rear link are automatically connected simultaneously with front and rear hitch brackets (support stays) provided in a mower deck (blade housing). However, with this arrangement, in the hitch brackets, there are only formed elongate holes opened along the vehicle body front/rear direction. Thus, for this connecting operation, a high-precision positioning is required between the mower deck and the vehicle body. Further, as an automatic connection arrangement relative to the mower deck is incorporated in a lift link mechanism, restriction is imposed on the designing of the structure of the lift link mechanism. For this reason, this automatic connection arrangement cannot be directly retrofitted with a conventional existing lift link mechanism. Moreover, with this connection arrangement, three points of the front-side hitch pin, the rear-side hitch pin and an output shaft side coupling need to be positioned with precision in three-dimensional manner with three points of the front-side hitch bracket, the rear-side hitch bracket and an input shaft side coupling, respectively. Hence, this connecting operation is difficult. 
     The U.S. Pat. No. 7,877,972 (FIG. 2, FIG. 4) and the U.S. Pat. No. 823,487 (FIG. 2, FIG. 4) too disclose automatic connection arrangements between a lift link mechanism and a mower deck (blade housing), including an automatic connection of power transmission paths. However, in these arrangements too, the automatic connection arrangement for the mower deck is integrally incorporated in the lift link mechanism. This results in specialization or peculiarity of the link link mechanism per se. Thus, when this automatic connection arrangement is employed, it is difficult to use a conventional lift link mechanism without any modification thereof. Further, as connection between the vehicle body and the blade housing and connection for power transmission need to be established simultaneously, a high skill and/or experience is required for the connecting operation. 
     SUMMARY OF THE INVENTION 
     In view of the above-described states of the art, there is a need for a mid-mount mower allowing facilitated connection arrangement between a vehicle body and a mower unit and connection arrangement of power transmission mechanism from the vehicle body to the mower unit and providing high reliability in effecting both of these connections. In accomplishing this object, it is also desired not to impose any substantial structural restraint on a conventional existing lift link mechanism. 
     According to one exemplary inventive mid-mount mower having a mower unit mounted under a vehicle body between front wheels and rear wheels, the mower comprises: 
     a lift link mechanism having a front link and a rear link provided in the vehicle body and spaced apart from each other in a vehicle body front/rear direction; 
     an intermediate structure interconnecting one end of the front link and one end of the rear link via a pivot axis; 
     a blade housing having an engaged portion engageable with an engaging portion of the intermediate structure; and 
     a guide face configured to guide the engaging portion and the engaged portion to an engaging position in association with a movement of the vehicle body in the vehicle body front/rear direction so as to establish connection between the blade housing placed on a ground surface and the intermediate structure. 
     With the above arrangement, for realization of automatic connection of the blade housing to the lift link mechanism, there is provided an intermediate structure for mediating establishment of this connection between the link link mechanism and the blade housing. Relative to the lift link mechanism, this intermediate structure is only connected pivotally to one end of the front link and one end of the rear link, which links together constituting the lift link mechanism. And, the engaging portion and the engaged portion used for automatic connection with the blade housing are provided in the intermediate structure and the blade housing, respectively. Therefore, essentially, it is also possible to use a conventional existing lift link mechanism as it is. Further, positioning or alignment between the engaging portion and the engaged portion at the time of connection establishment is guided by the guide face. Thus, a certain amount of positioning error can be tolerated in the movement of the vehicle body in the front/rear direction, so that the trouble for the driver of the vehicle body can be alleviated. 
     According to another exemplary inventive mid-mount mower having a mower unit mounted under a vehicle body between front wheels and rear wheels, the mower comprises: 
     a lift link mechanism having a front link and a rear link and configured to suspend the mower unit; 
     a blade housing having an engaged portion engageable with an engaging portion provided in the vehicle body in association with a movement of the vehicle body in a vehicle body front/rear direction; 
     a blade power transmission mechanism having a vehicle body side power transmission mechanism and a mower side power transmission mechanism as units separate from each other and having also a power coupling mechanism for coupling an output shaft of the vehicle body side power transmission mechanism with an input shaft of the mower side power transmission mechanism; and 
     a coupling operational tool for establishing coupling between the input shaft and the output shaft by displacing the power coupling mechanism in the vehicle body front/rear direction. 
     With the above arrangement, in association with a movement of the vehicle body in the vehicle body front/rear direction, firstly, the engaging portion provided on the side of the vehicle body comes into engagement with the engaged portion provided on the side of the blade housing. Upon establishment of this engagement between the engaging portion and the engaged portion, connection between the vehicle body and the mower unit is realized. As a result, the vehicle body and the blade housing are fixed in position relative to each other. Therefore, the subsequent coupling operation between the input shaft and the output shaft by the power coupling mechanism using the coupling operational tool can be carried out smoothly. That is, connection between the vehicle body and the mower unit and the connection of the power transmission mechanism from the vehicle body side to the mower unit side are effected in two steps, so that the connecting/mounting operation of the mower unit to the vehicle body can be carried out in a reliable manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic for explaining a first basic configuration of a mid-mount mower according to the present invention, showing a state immediately before an intermediate structure mower unit  4  is connected to a vehicle body, 
         FIG. 1B  is a schematic for explaining the first basic configuration of a mid-mount mower according to the present invention, showing a state in which the mower unit is connected to the vehicle body, 
         FIG. 2  is a side view showing a mid-mount mower as one of a first embodiment of the present invention, 
         FIG. 3  is a perspective view showing a mower unit, 
         FIG. 4  is a plan view showing a lift link mechanism and an intermediate structure, 
         FIG. 5  is a perspective view showing the lift link mechanism and the intermediate structure, 
         FIG. 6  is an exploded perspective view showing the lift link mechanism and the intermediate structure separately from each other, 
         FIG. 7A  is a section showing a flip-up mechanism for a gauge wheel, showing a state in which a rear gauge wheel is placed in contact with a ground surface, 
         FIG. 7B  is a section a flip-up mechanism for a gauge wheel, showing a state in which the rear gauge wheel is flipped up, 
         FIG. 8  is a plan view showing the mower unit, 
         FIG. 9  is a plan view showing the mower unit and the intermediate structure before coupling of a power coupling mechanism, 
         FIG. 10  is a plan view showing the mower unit and the intermediate structure after the coupling of the power coupling mechanism, 
         FIG. 11  is a vertical section showing a right-side functional portion of a first locking mechanism, 
         FIG. 12  is a side view showing the first locking mechanism before coupling and showing also a blade housing in its section, 
         FIG. 13  is a side view showing the first locking mechanism after the coupling and showing also the blade housing in its section, 
         FIG. 14  is a side view showing the mower unit lifted up by the lift link mechanism, 
         FIG. 15  is a perspective view showing the first locking mechanism and a second locking mechanism, 
         FIG. 16  is a perspective view showing a state in which a portion of connection between the intermediate structure and the blade housing is locked by the first locking mechanism and the second locking mechanism, 
         FIG. 17A  is a schematic showing the first basic configuration of the mid-mount mower according to the present invention, showing a state immediately before the intermediate structure mower unit  4  is connected to the vehicle body, 
         FIG. 17B  is a schematic showing the first basic configuration of the mid-mount mower according to the present invention, showing a state in which the intermediate structure mower unit  4  is connected to the vehicle body, 
         FIG. 18  is a side view showing a mid-mount mower as one of a second embodiment of the present invention, 
         FIG. 19  is a perspective view showing a mower unit, 
         FIG. 20  is a plan view showing a lift link mechanism and an intermediate structure, 
         FIG. 21  is a perspective view showing the lift link mechanism and the intermediate structure, 
         FIG. 22  is an exploded perspective view showing the lift link mechanism and the intermediate structure separately from each other, 
         FIG. 23  is a plan view showing the mower unit singly, 
         FIG. 24  is a plan view showing the mower unit and the intermediate structure before coupling of a power coupling mechanism, 
         FIG. 25  is a plan view showing the mower unit and the intermediate structure after coupling of the power coupling mechanism, 
         FIG. 26  is a perspective view showing the intermediate structure, 
         FIG. 27  is a perspective view showing a variation of an attaching unit provided in the intermediate structure, and 
         FIG. 28  is a plan view showing the intermediate structure shown in  FIG. 27 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     [First Embodiment] 
     Before a specific configuration of a first embodiment of a mid-mount mower according to the present invention is explained, a basic arrangement characterizing the present invention will be explained with reference to  FIG. 1A  and  FIG. 1B . A mid-mount mower (to be referred to simply as “mower” hereinafter) shown in  FIG. 1A  and  FIG. 1B  allows mounting of a mower unit  4  between front wheels  2   a  and rear wheels  2   b  under a vehicle body  1  having a vehicle body frame  10  as a principal constituent thereof. Downwardly of the vehicle body  1 , there is provided a lift link mechanism  3  consisting of a pair of left and right front links  31  and a pair of left and right rear links  32 . Via free ends of the front links  31  and free ends of the rear links  32 , an intermediate structure  6  is suspended. As the free ends of the front links  31  and the free ends of the rear links  32  are connected to the intermediate structure  6  via pivotal axes, in association with a pivotal movement of the lift link mechanism  3 , the intermediate structure  6  is lifted up/down relative to a ground surface. That is, the lift link mechanism  3  and the intermediate structure  6  together constitute an upper structure  9  for mounting the mower unit  4  to the vehicle body  1 . In this case, via this upper structure  9 , detachable connection is realized with a blade housing  40  as a principal component of the mower unit  4 . More particularly, on one hand, the upper structure  9  functions as an adaptor for interconnecting the vehicle body  1  and the mower unit  4 , with allowing the latter to be lifted up/down relative to the former. On the other hand, the intermediate structure  6  functions as an adaptor for connecting the lift link mechanism  3  to the mower unit  4 . For this reason, the intermediate structure  6  includes engaging portions  610 , whereas the blade housing  40  of the mower unit  4  includes engaged portions  620  engageable with the engaging portions  610 . 
       FIG. 1A  shows a state immediate before establishment of connection between the intermediate structure  6  and the mower unit  4 .  FIG. 1B  shows a state after the connection establishment. The trajectory of the front wheel  2   a  at the time of connection is illustrated by a dotted line in  FIG. 1A . As may be understood from the  FIG. 1A  and  FIG. 1B  illustrations, as the mower travels to ride over the mower unit  4  placed still on the ground surface with lateral orientation, the engaging portions  610  of the intermediate structure  6  come into engagement with the engaged portions  620  of the blade housing  40 , whereby connection is established between the mower unit  4  and the intermediate structure  6 . As a result, connection is realized between the mower unit  4  and the vehicle body  1  of the mower. For facilitating the above-described engagement between the engaging portions  610  of the intermediate structure  6  and the engaged portions  620  of the blade housing  40  in association with a movement of the vehicle body  1  in the vehicle body front/rear direction, guide faces  630  for guiding the engaging portions  610  to engagement positions for the engagement with the engaged portions  620  are formed in one or both of the intermediate structure  6  and the mower unit  4 . 
     The mode or form of engagement between the engaging portion  610  and the engaged portion  620  can vary in many ways. As one having a simple arrangement, a hole (slit)-pin engagement arrangement is preferably used which consists of an elongate slot extending in the vehicle body moving direction and an engaging pin engageable into this elongate slot. Alternatively, as another preferred arrangement, a recess-ball arrangement can be cited which consists of a curved recess opened in the vehicle body moving direction and a ball member coming into this curved recess. As a simple form of the guide face  630 , an inclined face can be used which is inclined relative to the vehicle body moving direction and configured to provide guiding to an appropriate position in association with traveling of the vehicle body. Especially, if such inclined face is provided in one or both of the engaging portion  610  and the engaged portion  620 , the arrangement can be simplified advantageously. 
     In general, the mower unit  4  has no power source of its own. Therefore, power from an engine  23  mounted on the mower is received via a working power transmission mechanism  25  to rotate a blade  43  provided in the blade housing  40 . This working power transmission mechanism  25  includes a vehicle body side power transmission mechanism  25 A and a mower side power transmission mechanism  25 B as separate units. In operation, when connection is established between a free shaft end (to be referred to also as “output shaft” hereinafter) of the vehicle body side power transmission mechanism  25 A and a free shaft end (to be referred to also as “input shaft” hereinafter) of the mower side power transmission mechanism  25 B, engine power is transmitted to the blade  43 . The output shaft of the vehicle body side power transmission mechanism  25 A and the input shaft of the mower side power transmission mechanism  25 B are connected or coupled via a power coupling mechanism  7 . Preferably, this power coupling mechanism  7  is supported to the intermediate structure  6 . However, the mechanism  7  can also be supported to the mower unit  4 . The power coupling mechanism  7  includes a coupling body  70  having a first coupling end to be connected to the output shaft and a second coupling end to be detachably connected to the input shaft. The coupling body  70  is relatively displaced or preferably, relatively displaced linearly, between a coupling position realizing the coupling between the vehicle body side power transmission mechanism  25 A and the mower side power transmission mechanism  25 B and a decoupling position realizing decoupling therebetween. 
     A locking mechanism(s) is provided for mechanically retaining the connecting positions between the engaging portions  610  and the engaged portions  620  realizing connection between the lift link mechanism  3  and the mower unit  4  via the intermediate structure  6  and the coupling position of the coupling body  70 . However, illustration of this locking mechanism is omitted in  FIG. 1A  and  FIG. 1B . Such locking mechanism can be a spring urging mechanism or retention mechanism. Preferably, an operation of the locking mechanism is effected by an operational member or tool extending to the periphery of a driver&#39;s seat  21 . Especially preferably, the connecting positions between the engaging portions  610  and the engaged portions  620  and the coupling position of the coupling body  70  are locked by a common locking mechanism. However, separate locking mechanisms can alternatively be provided for locking them individually. 
     The blade housing  40 , in order to vary its ground level (i.e. its level or height from the ground surface), includes a front gauge wheel unit  45  at a front lateral end of the vehicle body and a rear gauge wheel unit  46  at a rear lateral end of the vehicle body. At least one gauge wheel included in a gauge unit consisting of the front gauge wheel unit  45  and the rear gauge wheel unit  46  is shiftable to a position for bringing at least a portion of the blade housing  40  into contact with the ground surface. As at least a portion of the blade housing  40  is placed in contact with the ground surface, it is possible to restrict inadvertent movement of the mower unit  4  during a connecting operation of the mower unit  4 , which operation includes traveling of the mower to ride over the mower unit  4 . 
     Incidentally, in the foregoing explanation with reference to  FIG. 1A  and  FIG. 1B , the explanation was made that the intermediate structure  6  and the lift link mechanism  3  are provided as separate individual units. However, this explanation is applicable to an embodiment wherein the upper structure  9  comprised of the intermediate structure  6  and the lift link mechanism  3  integrated together functions as an attachment adaptor to the mower unit  4 . As long as the function of the intermediate structure  6  as an attachment adaptor to the mower unit  4  and the function of the lift link mechanism  3  for lifting up/down the mower unit  4  are realized, the configurations of the intermediate structure  6  and the lift link mechanism  3  can be freely designed. The present invention is not limited to the arrangement of the intermediate structure  6  and the lift link mechanism  30  being provided as separate individual units. 
     Next, with reference to drawings, one specific arrangement as a first embodiment will be explained.  FIG. 2  is a side view of a mower. This mower mounts a mower unit  4  between front wheels  2   a  and rear wheels  2   b . However, this mower can be used also as a standard tractor, with dismounting of the mower unit  4  therefrom. The mower includes a water-cooled diesel engine (to the referred to simply as “engine” hereinafter)  23  mounted on a front half portion of a vehicle body frame  10  and covered by a hood  11 , and a driver&#39;s seat  21  mounted on a rear half of the vehicle body frame  10 . The front wheels  2   a  are configured as steerable wheels operated by a steering wheel  22  and are configured as drive wheels also. As the mower is four-wheel drive type, the rear wheels  2   b  too are configured as drive wheels. On the rear half portion of the vehicle body frame  10 , a transmission case (to be referred to as “T/M case” hereinafter)  13  is mounted. 
     Power from the engine  23  is transmitted via a transmission shaft (not shown) constituting a power transmission mechanism  24  to a hydrostatic stepless speed changer (to be referred to as “HST” hereinafter)  15  connected to a front portion of the T/M case  13 . And, output from the HST  15  is transmitted to a gear speed changer (not shown) mounted inside the T/M case  13 . Power from the gear speed changer is divided within the T/M case  13  into a front wheel driving power and a rear wheel driving power. The front wheel driving power is transmitted to the front wheels  2   a  via a front wheel power transmission mechanism (constituting the power transmission mechanism  24 ) extending from the T/M case  13  to the front wheels  2   a . The rear wheel driving power is transmitted to the rear wheels  2   b  via a rear wheel power transmission mechanism (also constituting the power transmission mechanism  24 ) extending from the T/M case  13  to the rear wheels  2   b.    
     On the other hand, the power inputted to the HST  15  is transmitted in distribution to a first PTO (Power Take-OFF) shaft  16  mounted at the rear end of the T/M case  13  and oriented rearwards and a second PTO shaft  17  mounted to the bottom portion of the T/M case  13  and oriented forwardly. The first PTO shaft  16  and the second PTO shaft  17  together constitute a working power transmission mechanism  25  and the second PTO shaft  17  supplies power to the mower unit  4 . 
     At the rear portion of the T/M case  13 , there are provided such components as a pair of left and right lift arms  18  vertically pivoted by an operation of a lift cylinder (not shown) provided therein and a link mechanism  19  pivotally lifted up/down in operative association with the vertical pivotal movements of these lift arms  18 . As the lift cylinder, a single-action type hydraulic cylinder is employed. The link mechanism  19  includes e.g. a pair of left and right lower links  19   a  for allowing mounting and dismounting of a work implement (not shown) such as a rotary cultivator, a plow, etc. 
     This mower has the basic arrangement of the present invention explained above with reference to  FIG. 1A  and  FIG. 1B . Under the vehicle body frame  10  between the front wheels  2   a  and the rear wheels  2   b , the mower unit  4  is mounted. Between the vehicle body frame  10  and the mower unit  4 , the lift link mechanism  3  and the intermediate structure  6  are disposed. The lift link mechanism  3  supports the mower unit  4  in suspension via the intermediate structure  6  such that the mower unit  4  can be lifted up/down. The intermediate structure  6  functions as an adaptor and is connected on one hand to the lift link mechanism  3  and connected on the other hand to the mower unit  4 . 
     The lift link mechanism  3  includes a pair of left and right front links (pivot links)  31  assuming a rearwardly lowered inclined posture and interconnecting the front portion of the vehicle body frame  10  and the front portion of the intermediate structure  6 , and a pair of left and right rear links (pivot links)  32  assuming a rearwardly lowered inclined posture and interconnecting a longitudinal intermediate portion of the vehicle body frame  10  and the rear portion of the intermediate structure  6 . Thus, the mechanism  3  constitutes a parallel link mechanism for lifting up/down the mower unit  4  assuming a predetermined mowing posture, via the intermediate structure  6 . The left and right rear links  32  are coupled to to left and right lower links  19   a  of a link mechanism  19  via a coupling mechanism  34 . 
     The coupling mechanism  34  includes, e.g. a rotational shaft  341  oriented in the right/left direction and rotatably attached to the vehicle body frame  10 , a pair of left and right first coupling arms  342  extending to the forward side of the vehicle body from the rotational shaft  341  and mounted to this rotational shaft  341  integrally therewith, a pair of left and right second coupling arms  343  extending upwardly of the vehicle body from the rotational shaft  341  and mounted to this rotational shaft  341  integrally therewith, a pair of left and right coupling arms  344  provided at the rear portion of the T/M case  13 , a pair of left and right coupling rods  345  for coupling the left and right first coupling arms  342  to free ends of the rear links  32  corresponding thereto, a pair of left and right coupling rods  346  for coupling the left and right second coupling arms  343  to the coupling arms  344  corresponding thereto, etc. The left and right coupling arms  344  are pivotally mounted on support shafts  347  of the lower links  19   a  corresponding thereto. At upper portions of the left and right coupling arms  344 , as stoppers for restricting pivotal movement of the coupling arms  344  due to e.g. a load applied to the left and right rear links  32 , contact pieces are formed as bent portions configured to contact one side of upper edges of the lower links  19   a  of the link mechanism  19  from above. 
     That is, the mower unit  4  is connected to the vehicle body frame  10  via the lift link mechanism  3  and the intermediate structure  6 . Further, the lift link mechanism  3  is coupled to the link mechanism  19  via the coupling mechanism  34 . These arrangements enable lifting up/down of the mower unit  4  at the lower body portion of the tractor. 
     Though not shown in details in  FIG. 2 , the rotational shaft  341  integrally mounts a single third coupling arm  348  which extends toward the rear side of the vehicle body. The vehicle body frame  10  includes a lower limit setting mechanism  35  which receives the third coupling arm  348  pivoted upwards in association with a lower pivotal movement of the left and right rear links  32 , thereby to prevent a downward pivotal movement of the left and right rear links  32 . The lower limit setting mechanism  35  includes such components as an operational member  36  which can be operated pivotally about a vertical axis from the riding driving section, a tubular receiving portion  37  pivotable about the vertical axis together with the operational member  36 , etc. And, the lower edge of the receiving portion  37  receiving the third coupling arm  348  is formed like steps having different heights in the circumferential direction. 
     With the above-described arrangement in operation, by pivotally operating the operational member  36  about the vertical axis from the riding driving section, it is possible to vary a receiving height position of the receiving portion  37  to receive the third coupling arm  348  to a desired height position, whereby the lower limit position of the left and right rear links  22  relative to the vehicle body frame  10  (to be referred to as the lower limit position of the rear links  32 ) can be variably set easily. 
     That is, the lower limit position of the left and right rear links  32  can be variably set by this lower limit setting mechanism  35 . As a result, the lowering limit height of the mover unit  4  relative to the vehicle body frame  10  is changed. 
     In  FIG. 2 , the lift link mechanism  3 , the intermediate structure  6  and the mower unit  4  are shown. In this illustration, the intermediate structure  6  and the mower unit  4  are connected to each other. In  FIG. 3 , only the mower unit  4  is shown.  FIG. 4 ,  FIG. 5  and  FIG. 6  show the intermediate structure  6  connected to the lift link mechanism  3 .  FIG. 6  shows a state wherein the front links  31 , the rear links  32  and the intermediate structure  6  are separated from each other. As may be apparent from the  FIG. 3  illustration, the mower unit  4  includes a vertically oriented rotational shaft  43   a  for rotating three blades clockwise which are juxtaposed along the vehicle body traverse direction in a plan view, though not seen in  FIG. 3  illustration, and the blade housing  40  covering these blades from above. The blade housing  40  includes a top plate  41  and a side plate  42  extending downwards from the circumferential edge of the top plate  41 . The top plate  41  of the blade housing  40  mounts a blade driving power distribution mechanism  44 . Also, a transmission cover for covering from above a belt transmission mechanism  44   c  of the power distribution mechanism  44  is detachably mounted, but its illustration is omitted in  FIG. 3 . The blade housing  40 , at its front end region, forms an upwardly extending bulging portion extending along the right/left direction, thereby to create a transport passage for mowed grass therein. A discharge cover  40   a  is attached to the right end of the blade housing  40  forming a discharge outlet of this transport passage. 
     That is, this mower unit  4  is configured as a side-discharge type in which grass clippings cut by the three blades are transported through the transport passage formed inside the blade housing  40  by transporting air current generated in association with rotation of each blade and discharged through the discharge outlet at the right end of the unit  4  to the outside. 
     As shown in  FIG. 3 , at the left and right opposed ends of the front portion and the rear portion of the blade housing  40 , there are provided front gauge wheel units  45  each being height-adjustable and rear gauge wheel units  46  also each being height-adjustable. Incidentally, in  FIG. 7 , the rear gauge wheel unit  46  alone is shown in enlargement. Each front gauge wheel unit  45  includes a support bracket  45   b  having a vertical boss portion  45   c  and a front gauge wheel  45   a  mounted on an axle fixed to a sliding support shaft  45   d  slidably inserted into the vertical boss portion  45   c . The sliding support shaft  45   d  is fixed at a selected position by pin-fixing. The rear gauge wheel unit  46 , as shown in  FIG. 7  in details, includes a support bracket  46   b  having a vertical boss portion  46   c  flipped up by a flip-up mechanism  47 , and a rear gauge wheel  46   a  mounted on an axle fixed to a sliding support shaft  46   d  slidably inserted into the vertical boss portion  46   c . The sliding support shaft  46   d  too is fixed at a selected position by pin-fixing. The flip-up mechanism  47 , in this embodiment, is configured to retain a vertical posture of the sliding support shaft  45   d  by retaining, by a spring-urged pivot arm, the vertical boss portion  46   c  supported to the support bracket  46   b  to be pivotable about a horizontal axis (see  FIG. 7A ) and also to render the sliding support shaft  45   d . to an inclined posture by releasing the retention of the pivot arm (see  FIG. 7B ). Namely, this flip-up mechanism  47  has a function of flipping up the rear gauge wheel  46   a , by releasing the spring urging. When the rear gauge wheel  46   a  is flipped up, the lower end of the side plate  42  of the blade housing  40  comes into contact with the ground surface. With this, a large frictional force is applied between the blade housing  40  and the ground surface, so that even in the event of application of an external force thereto, movement of the blade housing  40  is restricted. 
     As shown clearly in  FIG. 8 , the power distribution mechanism  44  includes an input shaft (a constituent of the mower side power transmission mechanism  25 B) extending rearwards from a housing  44   a  disposed at the center of the blade housing  40 , and the belt transmission mechanism  44   c  for transmitting the power received by the input shaft  44   b  in distribution to three rotational shafts  43   a  to which the blades  43  are fixed respectively. 
     Next, with reference to  FIG. 4 ,  FIG. 5 ,  FIG. 6  and  FIG. 9  and  FIG. 10 , an embodiment of the intermediate structure  6  will be explained. This intermediate structure  6  has a framework consisting of a first member  61  and a second member  62  which extend in the vehicle body front/rear direction with forming a space therebetween, a front connecting member  63  interconnecting front portions of the first member  61  and the second member  62 , and a rear connecting member  64  interconnecting rear portions of the first member  61  and the second member  62 . The front connecting member  63  is a bar-like member having a convex portion at the center thereof, and at this convex portion, a hook-like free end of the front link  31  of the lift link mechanism  3  is pivotally retained. To the rear portions of the first member  61  and the second member  62 , the free end of the rear links  32  of the lift link mechanism  3  are pivotally pin-connected via link pins  39 . 
     To interconnect the intermediate structure member  6  and the blade housing  40 , the intermediate structure  6  includes engaging portions  610 , whereas the top plate  41  of the blade housing  40  includes engaged portions  620  engageable with the engaging portions  610 . In the instant embodiment, each engaging portion  610  includes a vehicle body side first front guide  611  provided as a bent portion formed in the region of the first member  61  connected to the connecting member  63 , a vehicle body side second front guide  612  provided as a bent portion formed in the region of the second member  62  connected to the connecting member  63 , a vehicle body side first rear guide  613  provided as an outwardly projecting bracket-like member disposed at the rear end of the first member  61 , and a vehicle body side second rear guide  614  provided as an outwardly projecting bracket-like member disposed at the rear end of the first member  61 . 
     Each engaged portion  620  includes a mower side first guide  621  and a mower side second front guide  622  which are disposed erect at the front region of the top plate  41  in distribution on the left and right sides, and a mower side first rear guide  623  and a mower side second rear guide  624  which are disposed erect at the rear region of the top plate  41  in distribution on the left and right sides. The mower side first front guide  621  and the vehicle body side first front guide  611 , the mower side second front guide  622  and the vehicle body side second front guide  612 , the mower side first rear guide  623  and the vehicle body side first rear guide  613 , the mower side second rear guide  624  and the vehicle body side second rear guide  614 , are disposed respectively at mutually engaging positions, under the interconnected state of the intermediate structure  6  and the blade housing  40 . 
     In this embodiment, the vehicle body side first front guide  611  and the vehicle body side second front guide  612  respectively include an engaging pin  69 A extending horizontally in an obliquely forward direction. Whereas, the vehicle body side first rear guide  613  and the vehicle body side second rear guide  614  respectively include an elongate slot  69 C extending horizontally in an oblique direction and opened to the front side. Further, the mower side first front guide  621  and the mower side second front guide  622  respectively include an elongate slot  69 B extending horizontally in an oblique direction and opened to the rear side. 
     Further, in a rear region of the top plate  41 , a rotational operation shaft  80  for a locking mechanism  8  to be described in details later extends in the vehicle body transverse direction (transverse direction). This rotational operation shaft  80  functions as an engaging pin engageable with the elongate slots  69 C of the vehicle body side first rear guide  613  and the vehicle body side second rear guide  614 . 
     The vehicle body side first front guide  611 , the vehicle body side second front guide  612 , the vehicle body side first rear guide  613 , the vehicle body side second rear guide  614 , and the mower side first front guide  621 , the mower side second front guide  622 , the mower side first rear guide  623 , the mower side second rear guide  624 , respectively include an inclined face which extends closer to a vehicle body longitudinal centerline as it extends forwardly. And, the respective corresponding inclined faces are formed so as to come into contact with each other substantially, under the interconnected state of the intermediate structure  6  and the blade housing  40 . Namely, these inclined faces function as “guide faces” for guiding the intermediate structure  6  to the position for connection with the mower housing  40  as the mower travels forwardly relative to the blade housing  40  placed on the ground surface. That is, the engaging portions  610  of the intermediate structure  6  and the engaged portions  620  of the blade housing  40  respectively include a guide face as an inclined face, and these guide faces come into contact with each other in association with a movement in the vehicle body front/rear direction. 
     The second PTO shaft  17  transmits power to the input shaft  44   b  (see  FIG. 6 ) of the power distribution mechanism  44  of the mower unit  4 , and the working power transmission mechanism  25  disposed therebetween is divided into the vehicle body side power transmission mechanism  25 A and the mower side power transmission mechanism  25 B. These mechanisms can be connected to or disconnected from each other by the power coupling mechanism  7  provided in the intermediate structure  6 . In the instant embodiment, the mower side power transmission mechanism  25 B includes a first universal joint  25   b  and the input shaft  44   b . The vehicle body side power transmission mechanism  25 A includes a relay shaft  25   a , the first universal joint  25   b  and a second universal joint  25   c . The first universal joint  25   b  interconnects the second PTO shaft  17  and the relay shaft  25   a . The second universal joint  25   c  interconnects the relay shaft  25   a  functioning as an output shaft of the vehicle body side power transmission mechanism  25 A and the input shaft  44   b  functioning as an input shaft of the mower side power transmission mechanism  25 B. This second universal joint  25   c  includes a spline-type connecting portion enabling connection to and disconnection from the input shaft  44   b . The mechanism for effecting these connection and disconnection is the power coupling mechanism  7 . The disconnecting state of the power coupling mechanism  7  is shown in  FIG. 9  and its connecting state is shown in  FIG. 10 . 
     As may be understood from  FIG. 9  and  FIG. 10 , the power coupling mechanism  7  includes a coupling body  70  which is provided as the second universal joint  25   c  in this embodiment, a coupling holding portion  73  configured to hold the coupling body  70  by surrounding it and holding it via an inner circumferential face thereof, and an attaching unit  75  for attaching the coupling holding portion  73  to the intermediate structure with allowing displacement of the coupling holding portion  73  in the vehicle body front/rear direction. The coupling body  70  includes a first connecting end  71  to be connected to the relay shaft  25   a  and a second connecting end  72  to be connected to the input shaft  44   b . The second connecting end  72  has an inner circumferential face formed with a spline engageable with the spline formed on the input shaft  44   b . The coupling holing portion  73  is a boss member having projections at opposed ends thereof. And, the coupling body  70  is fixed within a boss hole of this boss member. As the coupling holding portion  73  is moved toward the input shaft  44   b  of the power distribution mechanism  44 , the input shaft  44   b  and the second connecting end  72  are spline-engaged with each other. The attaching unit  75  is provided for realizing such movement of the coupling holding portion  73 . To this end, the attaching unit  75  is configured as a slider mechanism for moving the coupling holding portion  73 . As a force (e.g. an operational force by a driver) is applied from the outside to this slider mechanism, the coupling holding portion  73  is moved, thus realizing the connection of the power coupling mechanism  7 . In this embodiment, in order to cause a translation movement of the coupling holding portion  73 , there are provided a first leg portion  75   a  and a second leg portion  75   b  as a pair of slider rods, and guide holes as slide guides for the respective slider rods. The first leg portion  75   a  is a bar-like member fixed to the left end of the coupling holding portion  73  and extending rearwards therefrom. The second leg portion  75   b  is a bar-like member fixed to the right end of the coupling holding portion  73  and extending rearwards therefrom. The guide holes are through holes formed in a first bracket  65   a  and a second bracket  65   b  provided in the first member  61  and the second member  62 , respectively, as will be described later herein. The first leg portion  75   a  and the second leg portion  75   b  are inserted into these through holes, thus being slidably supported to the first bracket  65   a  and the second bracket  65   b.  Meanwhile, in the instant embodiment, the attaching unit  75  is supported to the first member  61  and the second member  62 , that is, to the intermediate structure  6 . However, instead of this, the attaching unit  75  can be supported to the vehicle body  1 , e.g. to the vehicle body frame  10 . 
     The intermediate structure  6  includes the first bracket  65   a  having a U-shape in its plan view and having its end connected to the first member  61  and extending toward the second member  62 , and the second bracket  65   b  having a U-shape in its plan view and having its end connected to the second member  62  and extending toward the first member  61 . Between the leading end of the first bracket  65   a  and the leading end of the second bracket  65   b , there is formed a gap through which the relay shaft  25   a  can pass. Further, the first bracket  65   a  defines, in its leading end region, a hole in which the first leg portion  75   a  is inserted and the second bracket  65   b  defines, in its leading end region, a hole in which the second leg portion  75   b  is inserted. With these, the first leg portion  75   a  and the second leg portion  75   b  are supported to the attaching unit  75  to be movable in the vehicle body front/rear direction. When the coupling holding portion  73  is moved together with the attaching unit  75  to a predetermined connecting position toward the input shaft  44   b  of the power distribution mechanism  44  under the interconnected state of the intermediate structure  6  and the blade housing  40 , spline connection is established between the second connecting end  72  of the coupling body (the second universal joint  25   c ) and the input shaft  44   b.    
     Incidentally, as shown in  FIG. 9  and  FIG. 10 , between the first leg portion  75   a  of the power distribution mechanism  44  and the first bracket  65   a  and also between the second leg portion  75   b  of the mechanism  44  and the second bracket  65   b , springs  76  are disposed for providing an urging force to release connection between the coupling body  70  held to the coupling holding portion  73  and the input shaft  44   b  of the power distribution mechanism  44 . Accordingly, when the locking mechanism  8  is pivoted in the direction for releasing lock, the coupling body  70  is automatically withdrawn from the input shaft  44   b . In  FIG. 9 , there is shown an expanded state of the spring  76 , that is, a state prior to establishment of spline-engagement between the input shaft  44   b  and the second connecting portion  72 . In  FIG. 10 , there is shown a compressed state of the spring  76 , that is, a state after establishment of the spline-engagement between the input shaft  44   b  and the second connecting portion  72 . 
     Next, with reference to  FIGS. 8 through 16 , the locking mechanism  8  provided in the blade housing  40  in this embodiment will be explained in details. As shown in the plan view of  FIG. 8 , the locking mechanism  8  includes a first locking mechanism  8 A for locking the coupling holding portion  73  at the connecting position and a second locking mechanism  8 B for locking the engaging portions  610  and the engaged portions  620  at the mutually engaged positions. The first locking mechanism  8 A and the second locking mechanism  8 B include a common rotational operation shaft  80 . And, this rotational operation shaft  80  extends in the vehicle body traverse direction in the rear end region of the top plate  41  of the blade housing  40  and is rotatably supported by a plurality of bearing stands. The rotational operation shaft  80  includes two first acting portions  81  for the first locking mechanism  8 A and two second acting portions  82  for the second locking mechanism  8 B. The first acting portions  81  are provided as arms configured to come into contact with the contacting portions provided at the rear ends of the first leg portion  75   a  and the second leg portion  75   b  of the power coupling mechanism  7  in association with rotation of the rotational operation shaft  80  to press the coupling holding portion  73  to the connecting position and holding this connecting position. The second acting portions  82  are provided as hook-like arms configured to come into contact with a pin-like projection  61   a  provided in the first member  61  and a pin-like projection  62   a  provided in the second member  62  and to hold these projections therein, thus retaining the engaging portions  610  and the engaged portions  620  at the engaging positions thereof, whereby the interconnection between the intermediate structure  6  and the blade housing  40  is retained. At one end of the rotational operation shaft  80 , there is fixed a rod-like operational arm  83  extending to the periphery of the driver&#39;s seat  21 . By an operation of the operational arm  83  by a driver seated at the driver&#39;s seat  21 , locking and lock-releasing of the locking mechanism  8  are possible. 
     With the mower according to the present invention, when the mower unit  4  is to be mounted to the vehicle body  1 , the mower is caused to travel forwardly to ride over the mower unit  4  placed laterally on the ground surface. To this end, the blade housing  40  includes a ride-over mechanism  5 . This ride-over mechanism  5 , as shown in  FIG. 3  and  FIG. 11 , is provided for each one of the left and right front wheels  2   a . And, the distance between the mechanisms  5  corresponds to the front-wheel tread width. Each ride-over mechanism  5  includes a bridge portion  50  extending along the front/rear direction upwardly of the belt transmission mechanism  44   c  mounted to the top plate  41  of the blade housing  40 , a front auxiliary plate  51  extending with an inclination from the front end of the bridge portion  50  toward the ground surface, and a rear auxiliary plate  52  extending with an inclination from the rear end of the bridge portion  50  toward the ground surface. The bridge portion  50  consists of a pair of arch-shaped rods having a flat intermediate portion, and a stepping plate disposed on the top faces of the intermediate portions of the pair of rods. Further, to opposed sides of the bridge portion  50 , side plates  53  are attached. The front auxiliary plate  51  and the rear auxiliary plate  52  are configured as slide type, so that these plates are retracted within the bridge portion  50  when out of use. This slide-type storage is realized by a guide pin  51   a  provided at the rear end of the front auxiliary plate  51  and a guide pin  52   a  and guide slits  53   a  provided at the front end of the rear auxiliary plate  52 . The guide slits  53   a  are formed in the respective side plates  53  substantially horizontally in the front/rear direction so as to respectively guide the guide pin  51   a  and the guide pin  52   a  inserted therein during the movement. But, these guide slits  53   a  are formed vertical at terminal ends thereof so as to retain the inclined postures of the front auxiliary plate  51  and the rear auxiliary plate  52  in a reliable manner, when the pins are withdrawn therefrom. 
     Firstly, for mounting the mower unit  4  to the lower body portion of the tractor, the intermediate structure  6  is lowered in advance to its lower limit position by an operation of the lift link mechanism  3 . In succession, the vehicle body  1  is caused to travel forwardly so that the front wheels  2   a  move above the blade housing  40  to ride over this housing with utilizing the ride-over mechanism  5  from the rear side of the mower unit  4 . When the front wheels  2   a  have passed over the blade housing  40 , the engaging portions  610  (the four guides  611 - 614  provided on the front, rear, left and right sides) provided in the intermediate structure  6  come into engagement with the engaged portions  620  (the four guides  621 - 624  provided on the front, rear, left and right sides) provided in the blade housing  40 . More particularly, the engaging pins  69 A provided in the vehicle body side first front guide  611  and the vehicle body side second front guide  612  are guided by the respective guide faces  630  and enter the elongate slots  69 B provided in the mower side first rear guide  613  and the mower side second rear guide  614 . In the course of this, the vehicle body side first rear guide  613  and the vehicle body side second rear guide  614  come into face contact with the mower side first rear guide  623  and the mower side second rear guide  624 , respectively and move into the regions restricted by these mower side first rear guide  623  and mower side second rear guide  624 . At the same time, into the slots  69  provided in the vehicle body side first rear guide  613  and the vehicle body side second rear guide  614 , the rotational operation shaft  80  of the lock mechanism  8  as an engaging pin enters. After the front wheels  2   a  have ridden past over the blade housing  40 , the vehicle body  1  is stopped. 
     At this point, on the axis of the input shaft  44   b  extending rearwards in the vehicle body front/rear direction of the power distribution mechanism  44  of the mower unit  4 , the axis of the coupling body  70  of the power coupling mechanism  7  provided in the intermediate structure  6  is positioned. Thus, the input shaft  44   b  and the coupling body  40  are aligned on the same axis in the vehicle body front/rear direction. 
     After the vehicle body  1  is stopped, the driver operates the operational arm  83  of the locking mechanism  8  to rotate the rotational operation shaft  80  (see  FIG. 13  and  FIG. 14 ). In response to this, the arms constituting the first acting portions  81  of the locking mechanism  8  press the rear ends (contacting portions) of the first leg portion  75   a  and the second leg portion  75   b  of the power coupling mechanism  7  provided in the intermediate structure  6 , thereby to move the coupling holding portion  73  together with the coupling body  70 , thus establishing interconnection between the input shaft  44   b  and the coupling body  70  (see  FIG. 16 ). Simultaneously, the two hook-like arms constituting the second acting portions  82  rotate and surround the pin-like projection  61   a  provided in the first member  61  and the pin-like projection  62   a  provided in the second member  62 . With this, the final engaged state between the engaging portions  610  and the engaged portions  620  is established. That is, according to the instant embodiment, the vehicle body side first front guide  611  and the mower side first front guide  621 , the vehicle body side second front guide  612  and the mower side second front guide  622 , the vehicle body side first rear guide  613  and the mower side first rear guide  623 , the vehicle body side second rear guide  614  and the mower side second rear guide  624  respectively are rendered to the respective engaged states. These engaged states will be maintained as long as the two hook-like arms as the second acting portions  82  keep pressing the projection  61   a  and the projection  62   a . This engagement retained sate is illustrated in enlargement in  FIG. 15 . Further, in order to maintain this engaged state, a locking device  84  for locking the rotational operation shaft  80  at its engaging rotational position is provided at the interconnecting position between the operational arm  83  and the rotational operation shaft  80 . The construction of this locking device  84  per se is well-known, thus detailed illustration thereof is omitted herein. Referring only briefly thereto, in this embodiment, the rotational operation shaft  80  is locked as a lock pin enters a lock hole at the engaging rotational position. And, as the lock pin moves out of the lock hole, locking of the rotational operation shaft  80  is released. Needless to say, any other locking arrangement can be employed also. 
     For dismounting the mower unit  4  from the vehicle body  1 , the lift link mechanism  3  is lowered so as to place the mower unit  4  onto the ground surface. Then, the driver operates the operational arm  83  of the locking mechanism  8  to rotate the rotational operation shaft  80  of the locking mechanism  8  to a locking release position. In response to this, the connection between the input shaft  44   b  and the coupling body  70  is released. In succession, the vehicle body  1  is caused to travel in reverse so that the front wheels  2   a  move above the blade housing  40  to ride over this housing with utilizing the ride-over mechanism  5  from the front side of the mower unit  4 . With this reverse traveling, the engaging portions  610  (the four guides  611 - 614  provided on the front, rear, left and right sides) provided in the intermediate structure  6  move out of the engaged portions  620  (the four guides  621 - 624  provided on the front, rear, left and right sides) provided in the blade housing  40 . After the front wheels  2   a  have ridden past over the blade housing  40 , the mower unit is released, so that this unit can be carried out freely. 
     [Second Embodiment] 
     Before a specific configuration of a second embodiment of a mid-mount mower according to the present invention is explained, a basic arrangement characterizing the present invention will be explained with reference to  FIG. 17A  and  FIG. 17B . The arrangement shown in  FIGS. 17A and 17B  differs from that shown in  FIGS. 1A and 1B  in that an operational tool  830  is provided in the arrangement shown in  FIGS. 1A and 1B . Here, the blade power transmission mechanism (working power transmission mechanism)  25  connectable to and disconnectable from a mower unit side shaft member and a vehicle body side shaft member in order to transmit rotational power of the engine  23  mounted on the mower to the blades  43  mounted to the blade housing  40  is rendered into a connected state for allowing the power transmission by using the operational tool  830 . 
     The coupling body  70  acting as an output shaft of the vehicle body side power transmission mechanism  25 A is relatively displaced, preferably linearly moved, between a connecting position realizing interconnection between the machine body side power transmission mechanism  25 A and the mower side power transmission mechanism  25 B and a releasing position realizing disconnection therebetween. This relative displacement is effected manually with using the operational tool  830 . Its operational force can use also a power of an electric motor, an electric cylinder, a hydraulic cylinder, etc. instead of the manual force. 
     Next, with reference to some drawings, one specific configuration as the second embodiment will be explained.  FIG. 18  is a side view of a mower. As many parts thereof are identical to those of the first embodiment explained above with reference to  FIGS. 1-16 , the following explanation will focus on difference from the first embodiment.  FIG. 20 ,  FIG. 21  and  FIG. 22  show a lift link mechanism  3  and an intermediate structure  6  in the second embodiment. The basic configurations thereof are identical to those of the first embodiment. 
     As shown in  FIG. 23 , at a rear region of a top plate  41  of a blade housing  40 , a locking fixing rod  800  constituting a second locking mechanism  8 B as one example of the locking mechanism  8  to be described in details later extends in the vehicle body traverse direction (traverse direction). A mower side second rear guide  624  and a vehicle body side second rear guide  614  form cutouts for avoiding interference with this locking fixing rod  800 . 
     As shown in  FIG. 24  and  FIG. 25 ,  FIG. 26  and  FIG. 27 , a power coupling mechanism  7  includes a coupling body  70  as a second universal joint  25   c , a coupling holding portion  730  surrounding the coupling body  70  and holding this coupling body  70  via its inner circumferential face, and an attaching unit  75  for attaching this coupling holding portion  730  to the intermediate structure, with allowing displacement of the portion  730  in the vehicle body front/rear direction. The coupling body  70  includes a first connecting end  71  to be connected to the relay shaft  25   a  and a second connecting end  72  to be connected to the input shaft  44   b.  The second connecting end  72  has an inner circumferential face formed with a spline engageable with the spline formed on the input shaft  44   b.  The coupling holding portion  730  is a plate-like boss member having extension pieces at opposed ends thereof. And, the coupling body  70  is fixed within a boss hole of this plate-like boss member. As the coupling holding portion  730  is moved toward the input shaft  44   b  of the power distribution mechanism  44 , the input shaft  44   b  and the second connecting end  72  are spline-engaged with each other. The attaching unit  75  is provided for realizing such movement of the coupling holding portion  730 . 
     To the above end, the attaching unit  75  is configured as a slider mechanism for moving the coupling holding portion  730 . As a force (e.g. an operational force by a driver) is applied from the outside to this slider mechanism, the coupling holding portion  730  is moved, thus realizing the connection of the power coupling mechanism  7 . In this embodiment, in order to cause a translation movement of the coupling holding portion  730 , there are provided a first leg portion  751  and a second leg portion  752  as a pair of slider rods, and guide holes as slide guides for the respective slider rods. The first leg portion  751  is configured as a bar-like member fixed to the left side extension of the coupling holding portion  730  and extending rearwards therefrom. The second leg portion  752  is configured as a bar-like member fixed to the right side extension piece of the coupling holding portion  730  and extending rearwards therefrom. The rear ends of the first leg portion  751  and the second leg portion  752  are interconnected via a connecting plate  753 . The attaching unit  75  includes, as bases, a first base plate  651  fixed to the first member  61  and a second base plate  652  fixed to the second member  62 . To the respect inner edges of the first base plate  651  and the second base plate  652 , a first bracket  653  and a second bracket  654  are fixed, respectively. Between the first bracket  653  and the second bracket  654 , there is formed a gap allowing passage of the relay shaft  25   a  therethrough. The first bracket  653  and the second bracket  654  respectively is configured as a C-shaped bent plate in its plan view and through holes are formed at its opposed end regions. These through holes function as guide holes for the first leg portion  751  and the second leg portion  752 . More particularly, the first leg portion  751  and the second leg portion  752  are inserted in the through holes formed coaxially at the opposed ends of the first bracket  653  and the second bracket  654  and slidably supported to the first bracket  653  and the second bracket  654 . An arch-shaped cover  656  is provided for partially covering, from above, the second universal joint  25   c  provided on the relay shaft  25   a  connected to the input shaft  44   b  of the mower side power transmission mechanism  25 B. This arch-like cover  656  is shown as being removed in the illustrations of  FIG. 26  and  FIG. 27 , but it is shown as being attached in the illustrations of  FIG. 24  and  FIG. 25 . 
     The operational lever  830  selectively providing the connected state and the disconnected state of the power transmission mechanism  7  is configured as an operational lever  830  pivotable about a pivotal vertical axis Pa as shown in  FIG. 26 , and a slit  831  is formed at one end thereof. And, in this slit  831 , a pin  832  fixed to the second leg portion  752  is inserted. Under the interconnected state of the intermediate structure  6  and the blade housing  40 , as the operational lever  830  is pivotally operated, the coupling body  70  is moved in the front/rear direction. With this, connection (splined connection) of the coupling body  70  acting as the output shaft of the vehicle body side power transmission mechanism  25 A and the input shaft  44   b  or disconnection thereof from the input shaft  44   b  are realized. 
     Between the first leg portion  751  and the first bracket  653  and also between the second leg portion  752  and the second bracket  654 , springs  76  are provided for urging in the direction of releasing the connection of the coupling body  70  held to the coupling holding portion  73  and the input shaft  44   b  of the power distribution mechanism  44 . Further, as shown in  FIG. 21  and  FIG. 22 , to the outer face of the first member  61  of the intermediate structure  6 , there is fixed a stopper plate  833  configured to hold the operational lever  830  at its pivotal position for interconnecting the coupling body  70  and the input shaft  44   b . This stopper plate  833  forms a cutout portion  834  which has a substantially same width as the operational lever  830  and which is opened downwards. This cutout portion  834  is configured to maintain the operational lever  830  at the pivotal position for interconnecting the coupling body  70  and the input shaft  44   b . The operational lever  830  and the cutout portion  834  constitute the first locking mechanism  8 A as one of the locking mechanism  8 . 
     Next, there will be explained the locking mechanism  8  for locking mounting of the mower unit  4  to the vehicle body  1 . This locking mechanism  8  includes the first locking mechanism  8 A for locking the coupling holding portion  73  at the connecting position and the second locking mechanism  8 B for locking the engaging portions  610  and the engaged portions  620  at the respective engaged positions. The first locking mechanism  8 A and the second locking mechanism  8 B are operatively coupled to each other via lock coupling link  840 , as may be understood from  FIG. 24 ,  FIG. 25  and  FIG. 26 . 
     As shown in  FIG. 25  and  FIG. 26 , between the rear end portion of the first member  61  and the rear end portion of the second member  62  of the intermediate structure  6  and on the front side of the rear connecting member  64  and parallel with this rear connecting member  64 , a rotational operation shaft  880  is rotatably mounted. On this rotational operation shaft  880 , a pair of left and right locking engagement pieces  820  are fixed with a spacing therebetween. Further, on this rotational operation shaft  880 , a connecting arm  841  is fixed. The connecting arm  841  is link-connected to the connecting plate  655  via the lock coupling link  840 . With this arrangement, sliding displacements of the first leg portion  751  and the second leg portion  752  are transmitted to the connecting arm  841 , whereby the rotational operation shaft  880  is rotated. The locking engagement pieces  820  are configured as hook-like arms, so that in association with rotation of the rotational operation shaft  880 , these pieces  820  engage with the lock fixing rod  800  fixed to the blade housing  40 . 
     A pivotal displacement of the operational lever  80  establishing interconnection between the coupling body  70  functioning as the output shaft of the vehicle body side power transmission mechanism  25 A and the input shaft  44   b  is converted into a rotational displacement for engaging the locking engagement pieces  820  to the lock fixing rod  800 . Namely, as described above, the operational lever  830  and a slit  844  formed in the stopper plate  833  together constitute the first locking mechanism  8 A as one component of the locking mechanism  8 , and the locking engagement pieces  820 , the lock fixing rod  800  and the lock coupling link  840  together constitute the second locking mechanism  8 B. 
     When the mower unit  4  is to be mounted to the vehicle body  1 , the mower is caused to travel forwardly to ride over the mower unit  4  placed laterally on the ground surface. To this end, the blade housing  40  includes a ride-over mechanism  5 . This ride-over mechanism  5 , as shown in  FIG. 19  and  FIG. 24 , is provided for each one of the left and right front wheels  2   a . And, the distance between the mechanisms  5  corresponds to the front-wheel tread width. Each ride-over mechanism  5  includes a bridge portion  500  extending along the front/rear direction upwardly of the belt transmission mechanism  44   c  mounted to the top plate  41  of the blade housing  40 , a front auxiliary plate  510  extending with an inclination from the front end of the bridge portion  500  toward the ground surface, and a rear auxiliary plate  520  extending with an inclination from the rear end of the bridge portion  500  toward the ground surface. The bridge portion  500  consists of a pair of arch-shaped frames having a flat intermediate portion and its cross section is formed like an upwardly opened channel. When not in use, the front auxiliary plate  510  and the rear auxiliary plate  520  are retracted and stored within the bridge portion  500 . The front auxiliary plate  510  and the second auxiliary plate  520  respectively include, at one end thereof, pins  511  and  521  projecting in the traverse direction. And, at front end and rear end of the bridge portion  500 , there are formed cutouts  501  for receiving these pins  511  and  521 . At the time of riding-over of the front wheels  2   a,  the front auxiliary plate  510  and the rear auxiliary plate  520  are inclined to orient their pins  511  and  521  upwards and these pins  511 ,  521  are inserted into the cutouts  501 . At the time of storage, the orientations of the front auxiliary plate  510  and the rear auxiliary plate  520  are reversed and these plates  510  and  520  are stored within the bridge portion  500  and also the pins  511  and  521  are inserted into the cutouts  501 . 
     Firstly, for mounting the mower unit  4  to the lower body portion of the tractor, the intermediate structure  6  is lowered in advance to its lower limit position by an operation of the lift link mechanism  3 . In succession, the vehicle body  1  is caused to travel forwardly so that the front wheels  2   a  move above the blade housing  40  to ride over this housing with utilizing the ride-over mechanism  5  from the rear side of the mower unit  4 . When the front wheels  2   a  have passed over the blade housing  40 , the engaging portions  610  (the four guides  611 - 614  provided on the front, rear, left and right sides) provided in the intermediate structure  6  come into engagement with the engaged portions  620  (the four guides  621 - 624  provided on the front, rear, left and right sides) provided in the blade housing  40 . More particularly, the engaging pins  69 A provided in the vehicle body side first front guide  611  and the vehicle body side second front guide  612  are guided by the respective guide faces  630  and enter the elongate slots  69 B provided in the mower side first front guide  621  and the mower side second front guide  622 . In the course of this, the vehicle body side first rear guide  613  and the vehicle body side second rear guide  614  come into face contact with the mower side first rear guide  623  and the mower side second rear guide  624 , respectively and move into the regions restricted by these mower side first rear guide  623  and mower side second rear guide  624 . 
     When the front wheels  2   a  have moved above the blade housing  40  to ride over this housing with utilizing the ride-over mechanism  5  from the rear side of the mower unit  4 , the vehicle body  1  is stopped. At this point, on the axis of the input shaft  44   b  extending rearwards in the vehicle body front/rear direction of the power distribution mechanism  44  of the mower unit  4 , the axis of the coupling body  70  of the power coupling mechanism  7  provided in the intermediate structure  6  is positioned. Thus, the input shaft  44   b  and the coupling body  40  are aligned on the same axis in the vehicle body front/rear direction. 
     After stopping of the vehicle body  1 , the driver pivotally operates the operational lever  830  to engage this operational lever  830  into the slit  831 . This pivotal displacement, on one hand, realizes interconnection between the coupling body  70  functioning as an output shaft of the vehicle body side power transmission mechanism  25 A and the input shaft  44   b , and this state is maintained by the function of the first locking mechanism  8 A and the above displacement realizes, on the other hand, engagement of the locking engagement piece  820  to the locking fixing rod  800 , and this state is maintained by the function of the second locking mechanism  8 B. 
     For dismounting the mower unit  4  from the vehicle body  1 , the lift link mechanism  3  is lowered so as to place the mower unit  4  onto the ground surface. Then, the driver operates the operational lever  830  to remove it from the slit  831 . The operational lever  830  disengaged from the slit  831  is pivoted to its home position by the resilience of the spring  76 . This pivotal displacement realizes, on one hand, disconnection between the coupling body  70  functioning as an output shaft of the vehicle body side power transmission mechanism  25 A and the input shaft  44   b , and realizes, on the other hand, disengagement of the locking engagement piece  820  from the locking fixing rod  800 . As a result, the interconnection between the blade housing  40  and the intermediate structure  6  is released. Further, the vehicle body  1  is caused to travel in reverse so that the front wheels  2   a  move above the blade housing  40  to ride over this housing with utilizing the ride-over mechanism  5  from the front side of the mower unit  4 . With this reverse traveling, the engaging portions  610  provided in the intermediate structure  6  move out of the engaged portions  620  provided in the blade housing  40 . After the front wheels  2   a  have ridden past over the blade housing  40 , the mower unit  4  is released, so that this unit can be carried out freely. 
     [Other Embodiments] 
     [1] The engagement arrangement for interconnecting the intermediate structure  6  and the blade housing  40 , consisting of the engaging portions  610  included in the intermediate structure  6  and the engaged portions  620  included in the blade housing  40  can be of any other engagement arrangement form than the hole-pin engagement described above, e.g. pawl engagement arrangement, as long as such other arrangement too realizes engagement in association with approaching in the vehicle body front/rear direction with forward traveling of the vehicle body  1  and disengagement in association with departing in the vehicle body front/rear direction with reverse traveling of the vehicle body  1 . Further alternatively, these different engagement arrangements can be used in combination. Also, in the foregoing embodiment, the number of the engaging connecting points created by the engaging portions  610  and the engaged portions  620  was four. However, it can be any number of two or more. 
     [2] In the foregoing embodiment, mutually contacting plate faces of the vehicle body side first front guide  611  and the mower side first front guide  621  were used as the guide faces  630 ; and mutually contacting plate faces of the vehicle body side second front guide  612  and the mower side second front guide  622  were used as the guide faces  630 . Instead, separate members can be provided for creating these guide faces  630 . Further, in the foregoing, the rotational operation shaft  80  of the locking mechanism  8  was employed as an engaging pin to come into engagement with the elongate slots  69 C provided in the vehicle body side first rear guide  613  and the vehicle body side second rear guide  614 . Instead, a separate engaging pin dedicated to this end can be provided in the blade housing  40 . 
     [3] The mower unit  4  can be configured as a rear-discharge type in which grass clippings are discharged rearwards from a discharge opening formed at the rear end of the blade housing  40 . Further alternatively, the mower unit  4  can be mulching type in which grass clippings cut by the blade are minced while being circulated inside the blade housing  40  and then dropped through an opening formed in the bottom of the blade housing  40  onto the ground surface. Furthermore, the number of blades to be provided in the mid-mount mower unit  4  and the transmission arrangement for the blade can vary in many ways. 
     [4]  FIG. 27  and  FIG. 28  show a further embodiment of an attaching unit  75  configured to move the coupling body  40  back and forth. In this further embodiment, instead of the first leg portion  751  and the second leg portion  752 , a first side plate  7501  and a second side plate  7502  are fixed to the opposed ends of the coupling holding portion  73  and extending in the front/rear direction. End portions of the first side plate  7501  and the second side plate  7502  corresponding to the coupling holding portion  73  are interconnected via an interconnecting plate  7503 . Further, the first base plate  651  forms a first guide plate  657  instead of the first bracket  653  and the second base plate  652  forms a second guide plate  658  instead of the second bracket  654 . The first guide plate  657  is fixed in position so as to contact the first side plate  7501 , and the second guide plate  658  is fixed in position so as to contact the second side plate  7502 . The first side plate  7501  and the second side plate  7502  respectively form guide grooves  7504  extending in the front/rear direction, whereas the first guide plate  657  and the second guide plate  658  respectively include guide pins  755  engageable into the guide grooves  7504  respectively. That is, with a guiding function of the guide grooves  7504  and the guide pins  755 , the coupling body  70  is moved back and forth. The leading end of the operational lever  830  is connected to the first side plate  7501 . In response to a pivotal displacement of the operational lever  830 , the first side plate  7501  and the second side plate  7502 , eventually, the coupling body  70 , are (is) moved back and forth. The lock coupling link  840  too is connected to the first side plate  7501 . 
     The present invention is applicable to a mower detachably mounting, between front wheels and rear wheels, a mower unit  4  of various types configured to be capable of being ridden over by the left and right front wheels. The configurations of the lift link mechanism and the mower unit  4  are not particularly limited in the present invention.