Abstract:
A PTO clutch for a work vehicle and an operating structure for the PTO clutch includes:
       a PTO clutch having a clutch member and receiving drive power from an engine;   a clutch control mechanically coupled to the clutch member for manually operating the PTO clutch via the clutch member;   a PTO brake disposed downstream of the PTO clutch with respect to a direction in which power is transmitted, the PTO brake being movable to a braking position in association with a clutch disengaging operation of the clutch member; and   a control retaining device for retaining the clutch control at a clutch disengaging position.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an operating apparatus for a PTO clutch mounted in a work vehicle such as an agricultural tractor. 
     A PTO clutch operating structure for an agricultural tractor is disclosed in e.g. JP2005-83488. In this construction, a PTO brake is arranged downstream (with respect to power transmitting direction) of a multi-disc type PTO clutch which is hydraulically operated. The PTO brake is operable for a braking operation, in association with a movement of a clutch operating piston member included in the PTO clutch in a clutch disengaging direction, thereby preventing continued inertial rotation of a utility implement which has been cut off from the PTO power transmission. 
     The above PTO clutch operating structure provides powerful clutch operations and braking operations by the hydraulic force. This construction, however, requires such hydraulic components as clutch operating switching valves, oil conduits, etc. Hence, the construction tends to be complicated and costly. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-described state of the art. 
     According to the present invention, there is proposed A PTO clutch for a work vehicle and an operating structure for the PTO clutch, comprising: 
     a PTO clutch having a clutch member and receiving drive power from an engine; 
     a clutch control mechanically coupled to the clutch member for manually operating the PTO clutch via the clutch member; 
     a PTO brake disposed downstream of the PTO clutch with respect to a direction in which power is transmitted, the PTO brake being movable to a braking position in association with a clutch disengaging operation of the clutch member; and 
     control retaining means for retaining the clutch control at a clutch disengaging position. 
     With the above-described construction, by disengaging the clutch control mechanically coupled to the clutch member and retaining the control at this position, it is possible to keep applying a braking force to a portion, downstream of the PTO clutch, in the PTO transmission line cut off from the power transmission, so that the continued inertial rotation of the PTO power-driven implement after the clutch disengagement can be avoided in a reliable manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a general side view of a tractor, 
         FIG. 2  is a side view in vertical section showing a transmission construction, 
         FIG. 3  is a side view showing a gear train included in the transmission construction, 
         FIG. 4  is a side view in vertical section showing a PTO clutch under a clutch engaged condition, 
         FIG. 5  is a side view in vertical section showing the PTO clutch under a clutch disengaged condition, 
         FIG. 6  is a side view showing a PTO clutch operating construction under the clutch engaged condition, 
         FIG. 7  is a side view showing the PTO clutch operating construction under the clutch disengaged condition, 
         FIG. 8  is a front view in vertical section showing the PTO clutch operating construction, and 
         FIG. 9  is a plan view showing a further embodiment of an control retaining means included in the PTO clutch operating construction. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the invention will be described next with reference to the accompanying drawings. 
       FIG. 1  shows a general side view of a four-wheel-driven agricultural tractor as an example of a work vehicle. In this agricultural tractor, for forming a vehicle body thereof, a clutch housing  2  connected to a rear side of an engine  1  and a transmission case  3  are connected to each other via a housing frame  4  made of sheet metal. A front frame  5  extending forwardly from a lower side of the engine  1  supports a front axle case  7  mounting steering front wheels  6 , with allowing rolling action of the front axle case  7  relative thereto. Rear wheels  8  are mounted at a rear portion of the transmission case  3 . 
     The transmission case  3  is formed by connecting a front case  3   f , a mid case  3   m  and a differential case  3   d  to each other. The rear wheels  8  are rotatably supported to the right and left sides of the differential case  3   d . To an upper portion of the differential case  3   d , there is connected a cylinder case  10  carrying lift arms  9 . The lift arms  9  are hydraulically driven to lift up/down a three-point link mechanism  11  provided for coupling of an implement. From a rear face of the differential case  3   d , a rear PTO shaft  12  projects rearwardly. From a lower portion side of the mid case  3   m , a mid PTO shaft  13  is disposed to project forwardly. 
     As shown in  FIG. 2 , the front case  3   f  accommodates therein a main gear speed-changing section  15  and a forward/reverse switchover section  16 . The mid case  3   m  accommodates therein an auxiliary gear speed-changing section  17 . 
     The main gear speed-changing section  15  is configured to vary the engine power inputted to an input shaft  18  in three speed stages and transmits thus speed-changed power to an intermediate shaft  19 . The forward/reverse switchover section  16  is configured to convert the speed-changed power from the intermediate shaft  19  into a forward or reverse rotational power and transmits this to an output shaft  20 . Hence, within the front case  3   f , it is possible to effect main speed changing operations in three forward stages and three reverse stages altogether. 
     More particularly, the input shaft  18  of the main gear speed-changing section  15  mounts a small free gear G 1  and a large free gear G 2 , and a shift gear G 3  having an intermediate diameter is splined between the small and large free gears G 1 , G 2 . The intermediate shaft  19  fixedly mounts a large gear G 4  and a small gear G 5  which constantly mesh respectively with the small, free gear G 1  and the large free gear G 2  and mounts also an intermediate diameter gear G 6 . In operation, when the shift gear G 3  is shifted forwardly to be spline-engaged with a boss portion of the small free gear G 1 , power is transmitted at a low speed (first speed) to the intermediate shaft  19  via the small free gear G 1  and the large gear G 4 . When the shift gear G 3  is shifted to a fore-and-aft intermediate position to be directly meshed with the intermediate gear G 5 , power is transmitted at a middle speed (second speed) to the intermediate shaft  19 . When the shift gear G 3  is shifted rearwardly to be spline-engaged with a boss portion of the large free gear G 2 , power is transmitted at a high speed (three speed) to the intermediate shaft  19  via the large free gear G 2  and the small gear G 5 . 
     The output shaft  20  mounts a forward rotation transmitting, free gear G 8  constantly meshed with a gear G 7  of the intermediate shaft  19  and a reverse rotation transmitting, free gear G 11  constantly meshed and operatively coupled with a further gear G 9  of the intermediate shaft  19 . Also, a shift sleeve S is splined on this output shaft  20 . In operation, as the shift sleeve S is shifted to be selectively meshed with either a boss portion of the forward rotation transmitting free gear G 8  or a boss portion of the reverse rotation transmitting free gear G 11 , the speed-changed power of the intermediate shaft  19  is transmitted in forward or reverse rotation to the output shaft  20 . 
     The auxiliary speed-changing section  17  effects speed changing operations in three stages between a transmission shaft (traveling transmission shaft)  21  connected end-to-end abutment with the output shaft  20  and an output shaft (bevel pinion shaft)  22 , so that a differential mechanism D is driven via a bevel pinion gear Gp mounted on a rear end of the output shaft  22  so as to drive the right and left rear wheels  8  differentially. 
     More particularly, the transmission shaft  21  mounts a large free gear G 12  and a small free gear G 13  at front and rear portions thereof, respectively. Further, a shift gear G 14  shiftable between the large and small free gears G 12 ,  13  is splined on this transmission shaft  21 . The bevel pinion shaft  22  fixedly mounts thereon a small gear G 15  constantly meshed with the large free gear G 12 , a large gear G 16  constantly meshed with the small free gear G 13 , and an intermediate diameter gear G 17  which can be directly meshed with the shift gear G 14 . In operation, when the shift gear G 14  is shifted rearwardly to bring its boss portion into meshed coupling with a boss portion of the small free gear G 13 , there is realized a “low speed” by the transmission with a gear ratio between the small free gear G 13  and the large gear G 16 . When the shift gear G 14  is shifted to a fore-and-aft intermediate position to be directly meshed with the intermediate diameter gear G 17 , there is realized an “intermediate speed” by the transmission with a gear ratio between the shift gear G 14  and the intermediate diameter gear G 17 . When the shift gear G 14  is shifted forwardly to bring its boss portion into meshed coupling with a boss portion of the large free gear G 12 , there is realized a “high speed” by the transmission with a gear ratio between the large free gear G 12  and the small gear G 15 . 
     At the front end of the bevel pinion shaft  22  which is speed-changed in the manners described above, there is fixed an output gear G 18  for transmitting power to the front wheels  6 . Further, a front wheel driving transmission shaft  23  is supported between and through the front case  3   f  and the mid case  3   m , so that power taken off this front wheel driving transmission shaft  23  is transmitted to the front axle case  7  via an unillustrated front wheel transmission structure. At a rear end of the front wheel driving transmission shaft  23 , there is splined a shift gear G 19 . In operation, when this shift gear G 19  is shifted forwardly to be meshed with the output gear G 18  of the bevel pinion shaft  22 , there is provided a four-wheel driving mode wherein a front wheel driving power of a speed synchronized with a rear wheel driving speed is taken off the front wheel driving transmission shaft  23 . Whereas, when the shift gear G 19  is shifted rearwardly to be released from the meshing with the output gear G 18 , there is provided a rear two-wheel driving mode wherein only the rear wheels  8  are driven while the driving of the front wheels  6  is stopped. 
     Next, the PTO transmission line will be described. 
     The rear end of the input shaft  18  supported through the upper portion of the front case  3   f  and a PTO transmission shaft  25  supported between and across the front case  3   f  and the mid case  3   m  are arranged in coaxial abutment to each other. And, via a one-way clutch  26  and a PTO clutch  27  provided at this abutment portion, the input shaft  18  and the PTO transmission shaft  25  are operatively coupled with each other. To the rear end of the PTO transmission shaft  25 , a relay transmission shaft  28  is connected coaxially. And, a small gear G 20  mounted at the rear end portion of this relay transmission shaft  28  is meshed with a large gear G 21  mounted on the rear PTO shaft  12 , so that the rear PTO shaft  12  can be driven at a constant speed, independently of the traveling line. 
     As shown in  FIG. 4 , the one-way clutch  26  includes a driving side clutch member  30  which is splined on a rear end portion of the input shaft  18  to be slidable in the fore and aft direction and slidably urged rearward by a spring  29  and a driven side transmission member  31  loosely fitted on a front end portion of the PTO transmission shaft  25  to be immovably axially. The clutch member  30  and the transmission member  31  are meshed and operatively coupled with each other via an inclined pawl engaging portion  32  provided adjacent mutually abutting ends of the members  30 ,  31 . The inclined pawl engaging portion  32  is provided with a pawl inclination direction set such that the driven side transmission member  31  may forcibly push forward the clutch member  30  against the spring  29 , while the transmission member  31  is allowed to rotate ahead of, i.e. preceding the rotation of, the clutch member  30  in the input shaft rotational direction. With this, it is possible to prevent the input shaft  18  from being rotated by reverse drive from the PTO transmission line. More particularly, when an implement having a large rotational inertia is rotatably driven by a PTO drive force, even if the main clutch is disengaged to stop vehicle travel and power transmission to the PTO transmission line is stopped, the input shaft  18  tends to be still driven by the rotational inertia of the implement, so that the vehicle may keep traveling inadvertently. The above-described arrangement effectively precludes this possibility. 
     As also shown in  FIG. 4 , the PTO clutch  27  is comprised of a meshing clutch consisting essentially of the transmission member  31  disposed on the driven side of the one-way clutch  26 , a transmission collar  33  loosely supported on the PTO transmission shaft  25  and a clutch member  34  splined on this transmission collar  33  to be slidable back and forth. In operation, when the clutch member  34  is slid forwardly to be engaged with and across the transmission member  31  and the transmission collar  33 , there is provided a “clutch engaged” condition for transmitting power from the transmission member  31  to the transmission collar  33 . Whereas, when the clutch member  34  is slid rearwardly to be released from the transmission member  31 , there is provided a “clutch disengaged” condition for interrupting the power transmission from the transmission member  31  to the transmission collar  33 . 
     At a rear portion of the PTO clutch  27 , there is disposed a PTO brake  35  operable to prevent inertial rotation of the transmission downstream side, in association with a “clutch disengaging” operation. The PTO brake  35  has a braking position and a non-braking position. This PTO brake  35  is constructed as a multi-disc friction brake having friction discs  36  splined on the transmission collar  33  and braking discs  37  non-rotatably engaged with a peripheral wall of the mid case  3   m , with the discs  36  and  37  being superposed in alternation each other. Between the clutch member  34  of the PTO clutch  27  and the PTO brake  35 , there is interposed a coil spring  38 . Under the “clutch engaged” condition with the clutch member  34  slid forwardly, the coil spring  38  has a non-compressed, free length, when the PTO brake  35  is not activated for braking (non-braking position). Under the “clutch disengaged” condition with the clutch member  34  slid rearwardly, the displacement of the clutch member  34  is transmitted via the coil spring  38  to the PTO brake  35 , so that the friction discs  36  and the braking discs  37  will be pressed against each other, thus applying a rotation braking force to the transmission collar  33 . 
     Rearwardly of the PTO brake  35 , there is provided a PTO mode selecting mechanism  40  capable of selectively providing a transmission mode in which the PTO power transmitted to the transmission collar  33  is transmitted only to the rear PTO shaft  12 , a further transmission mode in which the PTO power is transmitted only to the mid PTO shaft  13 , and a still further transmission mode in which the PTO power is transmitted both to the rear PTO shaft  12  and the mid PTO shaft  13 . 
     The mid PTO shaft  13  is supported to a PTO case  3   c  joined to the lower face of the mid case  3   m , so that the PTO power taken off an output gear G 22  loosely mounted on a rear portion of the PTO transmission shaft  25  is gear-transmitted to the mid PTO shaft  13 . More particularly, the output gear G 22  is operably meshed with a gear G 24  loosely mounted on the traveling transmission shaft  21  via a gear G 23  loosely mounted on the front wheel driving transmission shaft  23 , and a gear G 25  formed integral with this gear  24  is operably meshed with a gear G 27  formed integral on the mid PTO shaft  13  via a gear G 26  loosely mounted on an intermediate support shaft  39 . 
     The above-described PTO mode selecting mechanism  40  is configured to selectively provide the PTO modes by shifting, back and forth, a shift member  41  splined with an inner periphery of the transmission collar  33 . In operation, when the shift member  41  is shifted to a forward most position, the shift member  41  is meshed, in its inner periphery, with only a spline portion  25   a  of the PTO transmission shaft  25 , so that the power transmitted to the transmission collar  33  via the PTO clutch  27  is transmitted via the relay transmission shaft  28  to the rear PTO shaft  12  alone. 
     As shown in  FIG. 4 , when the shift member  41  is shifted to a fore-and-aft intermediate position, the shift member  41  is spline-engaged with the spline portion  25   a  of the PTO transmission shaft  25  and also with a boss portion of the output gear G 22 , so that the power transmitted to the transmission collar  33  via the PTO clutch  27  is transmitted to both the rear PTO shaft  12  and the mid PTO shaft  13 . 
     When the shift member  41  is shifted to a rear most position, the shift member  41  is spline-engaged with only the boss portion of the output gear G 22 , so that the power transmitted to the transmission collar  33  via the PTO clutch  27  is transmitted to the mid PTO shaft  13  alone. 
       FIGS. 6 through 9  show an operating structure for the PTO clutch  27 . 
     The clutch member  34  of the PTO clutch  27  is engaged with a shift fork  46  pivotally attached to a lateral wall of the mid case  3   m  via a fork shaft  45 . An outer end portion of this fork shaft  45  is operatively coupled, via a link mechanism  50 , with a clutch lever (an example of “clutch control”)  48  disposed erect on a side of a driving section to be pivotable back and forth via a support bracket  47 . 
     The link mechanism  50  consists essentially of an operational arm  51  pivotally connected to the support bracket  47 , a clutch arm  52  fixedly connected to an outer end of the fork shaft  45 , a link rod  53  interconnecting a free end of the operational arm  51  and a free end of the clutch arm  52 , and a toggle link  54  operably coupling the clutch lever  48  with the operational arm  51 . In operation, when the clutch lever  48  is operated to a clutch engaging position (ON) provided forwardly, the clutch member  34  is shifted forwardly, thus providing the “clutch engaged” condition. Whereas, when the clutch lever  48  is shifted to a clutch disengaging position (OFF) provided rearwardly, the clutch member  34  is shifted rearwardly, thus providing the “clutch disengaged” condition as well as a braked condition of the PTO brake  35 . 
     The toggle link  54  has a function as “control retaining means” for switchably moving the clutch lever  48  across a dead point between the clutch engaging position (ON) and the clutch disengaging position (OFF). More particularly, when the clutch lever  48  is operated rearward from the clutch engaging position (ON), an upper pivot (p) of the toggle link  54  is displaced rearward along an arcuate path extending around a pivot axis (q) of the clutch lever  48 , whereas a lower pivot (r) of the toggle link  54  is displaced downward along an arcuate path extending around a pivot axis (s) of the operational arm  51 , whereby the operational arm  51  is pivoted downward and the clutch member  34  is progressively moved rearward (clutch disengaging direction). 
     When the lower pivot (r) of the toggle link  54  has reached a virtual line (dead point) L connecting the upper pivot (p) of the toggle link  54  with the pivot axis (q) of the clutch lever  48 , the operational arm  51  assumes its most downwardly pivoted condition, when the PTO clutch  27  is disengaged completely and the PTO brake  35  is under the braking condition via the compressed coil spring  38 . As the clutch lever  48  is pivoted further rearward to reach an operation limit position contacting a base end boss  51   a  of the operational arm  51 , as shown in  FIG. 7 , the lower pivot (r) of the toggle link  54  has slightly passed forwardly the virtual line L connecting between the upper pivot (p) of the toggle link  54  and the pivot axis (q) of the clutch lever  48 . Under this condition, due to the elastic resilience from the compressed coil spring  38 , the clutch member  34  is slidably urged forward. With this forwardly urging force applied to the clutch member  34 , the clutch arm  52  is pivotally urged upward and the operational arm  51  operably connected to this clutch arm  52  is also pivotally urged upward. With this, the lower pivot (r) of the toggle link  54  is pushed upward, forwardly of the dead point L. So that, the clutch lever  48  is pivotally urged rearward, whereby the clutch lever  48  is retained at the clutch disengaging position (OFF). 
     Incidentally, the support bracket  47  mounts a limit switch  56  for detecting the operational arm  51  having been operated downward and located presently at the clutch disengaging position. And, this limit switch  56  is connected to an engine starting circuit so as to allow start of the engine  1  only when the limit switch  56  is detecting disengagement of the PTO clutch  27 . 
     To an outward projecting portion of the fork shaft  45 , a disc  57  is fixedly attached. And, there is provided a detent mechanism  60  for engaging a spring-biased detent ball  59  within a notch  58  formed in an outer periphery of the disc  57 . This detent mechanism  60  is activated for the engagement when the clutch member  34  is located at the clutch engaging position, thus retaining the clutch engaged condition stably. Incidentally, a base plate  61   a  of a holder  61  supporting the detent ball  59  is engaged with an outer peripheral groove  62  of the fork shaft  45 , so that this plate is utilized as an anti-withdrawal member for the fork shaft  45 . 
     Other Embodiments 
     (1) In the foregoing embodiment, the link mechanism for operably coupling the clutch lever (clutch control)  48  with the fork shaft  45  incorporates therein the control retaining means for switchably moving the clutch lever  48  across the dead point L between the clutch engaging position (ON) and the clutch disengaging position (OFF). Alternatively, the clutch lever  48  and the fork shaft  45  may be operatively coupled via a simple link mechanism and the clutch lever  48  may be retained in position by a dedicated control retaining means. 
     (2) As shown in  FIG. 9 , as a simple modified control retaining means, the clutch lever (clutch control)  48  may be configured to be operable or deformable in a lateral direction normal to the pivot operating direction, and the clutch lever  48  may be retained in a recess  66  defined in the lever guide  65 , thus being retained at the clutch disengaging position (OFF). 
     (3) Further, the control retaining means can be formed with utilizing a curved toggle link  54  for passing a dead point. 
     (4) The PTO operating tool for operating the PTO clutch  27  and the PTO brake  35  can alternatively utilize a PTO pedal which can be foot-operated forwardly and reversely.