Riding lawn tractor
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a tiding lawn tractor in which a mower unit may be coupled to a tractor body through front and mar links. More particularly, the invention relates to a coupling mechanism between the mower unit and the front links connected to the tractor body. 
     2. Description of the Prior Art 
     A connection between a mower unit and front links connected to a tractor body in a conventional riding lawn tractor is disclosed in Japanese Patent Publication Kokai No. 6-253641, for example. This connection includes a headed pin extending through bores formed in rear end regions of the front links, and through mating bores formed in a bracket fixed to the front of a blade housing of the mower unit. The headed pin defines bores in the head and an opposite end region, and retainer pins or the like are passed through the bores to retain the headed pin in place. To detach the mower unit from the tractor body, the retainer pins are removed, and then the headed pin is slid transversely of the tractor body out of the bores of the front links and the bracket of the mower unit. 
     The connection between the front links and the bracket of the mower unit is situated in a confined space under the tractor body. It is a troublesome operation to attach or detach the right and left retainer pins and the connecting pin. This lowers operating efficiency in coupling and uncoupling the mower unit and front links. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a coupling structure between coupling links and a bracket on a mower unit, which facilitates operations to couple and uncouple a tractor body and the mower unit, and in which front links do not easily or inadvertently come off once the links are coupled. 
     The above object is fulfilled, according to the present invention, by a coupling mechanism comprising: 
     an engaging device including: 
     a first cross rod extending parallel to a transverse shaft of the tractor body; 
     a second cross rod spaced from the first cross rod and extending substantially parallel to the first cross rod; and 
     a connecting device for interconnecting the first cross rod and the second cross rod; and 
     receiver brackets each defining a groove for simultaneously receiving part of the first cross rod and part of the second cross rod, the groove including a first groove portion having a length substantially corresponding a distance between the first cross rod and the second cross rod, and a second groove portion extending from the first groove portion in a direction substantially perpendicular thereto and opening to ambient. 
     According to the above construction, in a coupled state, front links are engaged with the receiver brackets through the first and second cross rods. When the tractor moves forward, the front links haul a working unit through the contact between the first cross rod and the first groove portion of each receiver bracket. When the tractor moves backward, the front links push the working unit backward which would otherwise stand still in contact with the ground. At this time, the working unit is driven backward, with the second cross rod contacting walls of the first groove portions, thereby preventing the front links from shifting backward out of the receiver brackets. 
     For disengaging the front links from the receiver brackets, forward ends of the front links are detached from the tractor body first. Then, the second cross rod is moved along the second groove portion of each receiver bracket and out of the bracket. Subsequently, the first cross rod remaining in the groove is removed from the first groove portion and then from the second groove portion. Thus, the engaging device, i.e. the first and second cross rods, may be removed from the receiver brackets with ease. 
     Consequently, instead of employing a complicated coupling device having a pin to be moved transversely through bores formed in two components, an engaging or disengaging operation is carded out simply by dropping the two cross rods into the grooves or picking up the rods therefrom. This construction is also effective to prevent the links from inadvertently becoming disengaged as a result of movement of the tractor body. 
     Other features and advantages of the present invention will be apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation of a riding lawn tractor according to the present invention. 
     FIG. 2 is a side view showing a front link and a mower unit coupled to each other. 
     FIG. 3 is a side view similar to FIG. 2 and showing a second cross rod of an engaging device engaging a second groove portion. 
     FIG. 4 is a plan view of the mower unit and coupling mechanism. 
     FIG. 5 is a plan view, partly in section, showing a coupling mechanism between a tractor body and forward ends of front links. 
     FIG. 6 is a front view, partly in section, showing a structure for fixing the mower unit in an upper limit position to the tractor body, the mower unit in a lower position being shown in so-dot-and-dash lines. 
     FIG. 7 is a fragmentary plan view showing front links and a mower unit coupled to each other according to another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a mid-mount type riding lawn tractor having a mower unit M disposed in a space under a tractor body A between front wheels 1 and rear wheels 2. The mower unit M is vertically movably connected to the tractor body A through a parallelogram link mechanism R1 including front links 3 and rear links 4. When lift arms 5 are operated to cause lower links 6 to pivot vertically, contact links 7 constituting a link mechanism R2 pivot through contact with upper surfaces of the lower links 6, thereby moving the mower unit M vertically. 
     The tractor body A has brackets 8 extending downward and supporting a pivotable hook 10. The front links 3 are locked to and unlocked from the brackets 8 through pivotal movement of the hook 10. A lever 9 is fixed to the hook 10 for pivoting the hook 10. The hook 10 may be retained by a lock pin 11 in a position for locking the front links 3. As shown in FIG. 5, the lock pin 11 has a handle, is slidable transversely relative to the brackets 8, and is spring-loaded toward a locking position. 
     The front links 3, which are a pair of right and left front links, have forward ends thereof interconnected through a transverse rod 3a, and rear ends interconnected through a first cross rod 3b. A pair of right and left coupling plates 12 are pivotally connected to the first cross rod 3b. Free ends of the coupling plates 12 are interconnected through a second cross rod 12a. As shown in FIG. 2, the mower unit M includes a blade housing 13 having mounting brackets 14 attached to the front thereof. Each mounting bracket 14 defines an engaging groove 15 for receiving and engaging the first and second cross rods 3b and 12a. The engaging groove 15 has an opening directed upwardly and forwardly. The engaging groove 15 includes a second groove portion 15b defining a zigzag passage extending from the opening. The engaging groove 15 is substantially L-shaped as a whole when seen from a side of the tractor body A. That is, the second groove portion 15b extends substantially downwardly and rearwardly, and is then curved in a predetermined position. A first groove portion 15a extends downwardly and forwardly from the curved position to a closed end. The first groove portion 15a has a length substantially corresponding to a length formed by the first cross rod 3b and second cross rod 12a interconnected by the pair of coupling plates 12. 
     As shown in FIG. 1, the rear links 4 also comprise a pair of right and left links. Each rear link 4 has a forward end thereof pivotally connected to a bracket 16 on the tractor body A through a coupling pin 17, and a rear end connected to a link attaching bracket 18 in a rearward position of the mower unit M through a lock pin 19 slidable transversely of the tractor body A. The lock pin 19 has a handle for sliding it transversely of the tractor body A, to lock and unlock the rear link 4. The lock pin 19 is spring-loaded toward a locking position. 
     To detach the mower unit M from the tractor body A, the forward ends of the front links 3 are first disengaged from the tractor body A. Then, the rear ends of the front links 3 are disengaged from the mower unit M. Subsequently, the rear ends of the rear links 4 are uncoupled from the mower unit M. 
     As shown in FIGS. 1, 4 and 6, the mower unit M includes anti-chatter devices 21 mounted on an upper surface of the blade housing 13 of the mower unit M. When the mower unit M is raised to an upper limit position, plates 20 attached to the tractor body A are press fit in the anti-chatter devices 21. This absorbs transverse play occurring in connections between the front and rear links 3 and 4 and the brackets 8 and 16. Each of the anti-chatter devices 21 is in the form of a U-shaped metal element. An upper end region of the outer portion of the U-shaped metal element is bent sideways. In the course of upward movement of the mower unit M, the plate 20 on the tractor body A contacts the bent upper end region. With a further upward movement of the mower unit M, the plate 20 is guided by the bent region to enter the U-shaped metal element acting as the anti-chatter device 21. The pair of plates 20 have a predetermined distance therebetween so that each plate 20 is in pressure contact with the outer portion of the anti-chatter device 21 leaving no space in between. A pin 22 is used to interconnect each plate 20 and anti-chatter device 21 in pressure contact with each other. Thus, longitudinal and transverse chattering between the tractor body A and the mower unit M in the upper limit position is avoided. 
     As shown in FIG. 4, a blade driving belt 23 is in contact with a belt presser pin 24. A sound proofing cover 25 is mounted peripherally of this pin 24 to suppress contact noise. 
     The second cross rod 12a may extend laterally outwardly of one of the coupling plates 12 to be used as a handle. 
     The front links 3 may have modified engaging devices as shown in FIG. 7. In this example, the rear ends of front links 3 are not directly interconnected, but include bifurcate elements 3c extending therefrom, respectively. Each bifurcate element 3c has bores formed in free end regions thereof for rotatably receiving a rod 3b. A coupling plate 12 extends from an inward end of each rod 3b. The coupling plates 12 are interconnected at free ends thereof by a cross rod 12a. For coupling the engaging device to the brackets 14, a portion of each rod 3b between the two prongs of the bifurcate element 3c and each end of the cross rod 12a may be fitted into the first groove portion 15a.