Abstract:
A tractor with a PTO apparatus, comprises: a plurality of wheels; a vehicle body supported by the plurality of wheels; an engine supported on the vehicle body; a rear PTO shaft disposed at a rear of the vehicle body for transmitting power from the engine; a mid-PTO shaft disposed under the vehicle body for transmitting power from the engine; a PTO mode selecting device having a first position for transmitting power only to the rear PTO shaft, a second position for transmitting power to both the rear PTO shaft and said mid-PTO shaft, and a third position for transmitting power only to said mid-PTO shaft; a PTO clutch disposed on a transmission line upstream of said PTO mode selecting device and switchable between an engaged position and a disengaged position; and a restricting mechanism for preventing a change operation of said PTO mode selecting device when said PTO clutch is in the engaged position, and permitting the change operation of said PTO mode selecting device when said PTO clutch is in the disengaged position.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to a tractor with a PTO apparatus having a rear PTO shaft disposed at the rear of a vehicle body and a mid-PTO shaft disposed under the vehicle body.  
         [0002]     A known tractor includes a rear PTO shaft disposed at the rear of a vehicle body, a mid-PTO shaft disposed under the vehicle body, and a PTO mode selecting mechanism for selecting an output state from three output states. The three output states are a state of outputting power only from the rear PTO shaft, a state of outputting power from both the rear PTO shaft and mid-PTO shaft, and a state of outputting power only from the mid-PTO shaft. The tractor further includes a PTO clutch disposed on a power transmission line upstream of the PTO mode selecting mechanism (see Japanese Application “Kokai” No. 5-162551,  FIG. 7 , for example).  
         [0003]     The above PTO transmission structure has excellent practical utility for enabling a wide range of operations using the rear PTO shaft and mid-PTO shaft. However, the PTO mode selecting mechanism could be operated inadvertently without disengaging the PTO clutch, thereby abruptly rotating the PTO shafts from stationary state, or abruptly stopping the PTO shafts in rotation. In this way, an excessive force may be applied to meshed gears or splines on the PTO transmission line to damage such components or produce a loud noise.  
       SUMMARY OF THE INVENTION  
       [0004]     The object of this invention is to solve the above-noted problems. A tractor with a PTO apparatus comprises: a plurality of wheels; a vehicle body supported by said plurality of wheels; an engine supported on said vehicle body; a rear PTO shaft disposed at a rear of said vehicle body for transmitting power from said engine; a mid-PTO shaft disposed under said vehicle body for transmitting power from said engine; a PTO mode selecting device having a first position for transmitting power only to said rear PTO shaft, a second position for transmitting power to both said rear PTO shaft and said mid-PTO shaft, and a third position for transmitting power only to said mid-PTO shaft; a PTO clutch disposed on a transmission line upstream of said PTO mode selecting device and switchable between an engaged position and a disengaged position; and a restricting mechanism for preventing a change operation of said PTO mode selecting device when said PTO clutch is in the engaged position, and permitting the change operation of said PTO mode selecting device when said PTO clutch is in the disengaged position.  
         [0005]     According to the above construction, the PTO mode selecting device is switchable only when the PTO clutch disposed on the transmission line upstream of the PTO mode selecting device is in the disengaged position. This feature precludes the possibility of abruptly rotating the PTO shafts from stationary state or abruptly stopping the PTO shafts in rotation.  
         [0006]     Thus, the apparatus according to this invention contributes to improvement in the durability and operability of the PTO transmission system.  
         [0007]     The disclosures of Japanese Patent Applications 2004-300336 filed on Oct. 14, 2004 and 2004-188316 filed on Jun. 24, 2004 are incorporated by reference. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a side elevation of a tractor;  
         [0009]      FIG. 2  is a side view in vertical section of a front wheel transmission structure;  
         [0010]      FIG. 3  is a side view in vertical section of a transmission structure;  
         [0011]      FIG. 4  is a schematic view showing gear trains of the transmission structure;  
         [0012]      FIG. 5  is a side view in vertical section of a front wheel change speed mechanism in a standard four wheel drive mode;  
         [0013]      FIG. 6  is a side view in vertical section of the front wheel change speed mechanism in a front wheel accelerating drive mode;  
         [0014]      FIG. 7  is a hydraulic circuit diagram;  
         [0015]      FIG. 8  is a side view in vertical section of a PTO mode selecting device;  
         [0016]      FIG. 9  is a side view in vertical section of the PTO mode selecting device;  
         [0017]      FIG. 10  is a side view in vertical section of the PTO mode selecting device;  
         [0018]      FIG. 11  is a side view showing a control structure for controlling the PTO mode selecting device;  
         [0019]      FIG. 12  is a front view showing the control structure for controlling the PTO mode selecting device;  
         [0020]      FIG. 13  is a plan view of a rear portion of a vehicle body;  
         [0021]      FIG. 14  is a plan view of a lever guide;  
         [0022]      FIG. 15  is a sectional view showing a proximal end of a position control lever;  
         [0023]      FIG. 16  is a view showing characteristics of a plate spring;  
         [0024]      FIG. 17  is a plan view showing a lever guide in another embodiment;  
         [0025]      FIG. 18  is a side view showing a lever guide for a PTO system according to this invention;  
         [0026]      FIG. 19  is a plan view showing the lever guide of the PTO system according to this invention; and  
         [0027]      FIG. 20  is a perspective view showing components of a restricting device according to this invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Preferred embodiments of this invention will be described hereinafter with reference to the drawings.  
         [0029]      FIG. 1  shows a side elevation of a tractor according to this invention. The tractor includes a clutch housing  2  directly connected to the back of an engine  1 , a housing frame  4  of sheet metal structure, a main transmission  12  in the form of a hydrostatic stepless transmission (HST), a transmission case  3  and a differential case  5 . These components are successively connected in tandem to constitute a vehicle body. The differential case  5  rotatably supports right and left rear wheels  6 , and has a rear PTO shaft  7  projecting rearward. Right and left front wheels  8  are dirigibly supported by a front axle case  9  attached for rolling motion to a lower position of a front frame  10  connected to the engine  1 .  
         [0030]     Next, the structure of a transmission system of this tractor will be described. As shown in  FIG. 2 , the clutch housing  2  has a main clutch C 1  of the single plate, dry type mounted in an upper portion thereof. As shown in  FIG. 3 , the main transmission  12  includes, arranged in upper and lower positions thereof, a variable displacement pump P of the axial plunger type and a fixed displacement motor M of the axial plunger type. A main output shaft  14  projecting rearward from the clutch housing  2  is interlocked, through a main transmission shaft  15 , to an input shaft  13  projecting forward from the upper position of the main transmission  12 .  
         [0031]     A well-known structure is employed for the main transmission  12  for driving an output shaft  16  of the motor M at steplessly variable speeds forward or backward by varying a swash plate angle of the pump P to change the amount and direction of pressure oil discharge. Thus, the main transmission  12  is operable by a change pedal, not shown, disposed in a right-hand position on a driving platform, to effect stepless speed changing and backward and forward switching from a zero speed start.  
         [0032]     The transmission case  3  is open at the front and rear ends, and has an intermediate partition wall  3   a  located in a fore and aft intermediate position thereof to divide its interior into a front portion and a rear portion. A transmission shaft  17  of the propelling system supported by the intermediate partition wall  3   a  and a front wall  5   a  of the differential case  5  is coaxially coupled to the output shaft  16  of the motor M. In the rear portion of the transmission case  3 , a bevel pinion shaft  18  acting as a final transmission shaft is supported by the intermediate partition wall  3   a  and the front wall  5   a  of the differential case  5 . An auxiliary change speed gear mechanism  19  of the propelling system is mounted between the transmission shaft  17  and the bevel pinion shaft  18 . The auxiliary change speed gear mechanism  19  has a shift gear G 1  splined to the transmission shaft  17  to be shiftable to rotate the bevel pinion shafts  18  at three speeds. Thus, the right and left rear wheels  6  are driven at variable speeds through a differential mechanism D meshed with a bevel pinion gear Gp.  
         [0033]     Specifically, the transmission shaft  17  has a large diameter loose fit gear G 2  mounted on a forward part thereof, and a small diameter loose fit gear G 3  mounted on a rearward part thereof. The bevel pinion shaft  18  has a small diameter gear G 4  fixed thereto and in constant mesh with the large diameter loose fit gear G 2 , and a large diameter gear G 5  fixed thereto and in constant mesh with the small diameter loose fit gear G 3 . The bevel pinion shaft  18  further includes an intermediate diameter gear G 6  fixed thereto to be meshable directly with the shift gear G 1 . When the shift gear G 1  is shifted rearward to couple a boss portion thereof to a boss portion of the small diameter loose fit gear G 3 , a “low speed” is provided by the gear ratio between the small diameter loose fit gear G 3  and large diameter gear G 5 . When the shift gear G 1  is shifted to a fore and aft intermediate position to mesh directly with the intermediate gear G 6 , an “intermediate speed” is provided by the gear ratio between the shift gear G 1  and intermediate gear G 6 . When the shift gear G 1  is shifted forward to couple a boss portion thereof to a boss portion of the large diameter loose fit gear G 2 , a “high speed” is provided by the gear ratio between the large diameter loose fit gear G 2  and small diameter gear G 4 .  
         [0034]     As described above, the bevel pinion shaft  18  is hydraulically and steplessly changed to different forward or backward speeds, and changed to three speeds by the auxiliary change speed gear mechanism  19 . The bevel pinion shaft  18  has an output gear G 7  fixed to a forward end thereof for power transmission to the front wheels  8 . Further, a front wheel driving transmission shaft  20  extends through, and is supported by, the intermediate partition wall  3   a  and the main transmission  12 . The front wheel driving transmission shaft  20  has a shift gear G 8  splined to a rear end region thereof. This shift gear G 8  is shiftable forward into mesh with the output gear G 7  on the bevel pinion shaft  18 . This provides a four wheel drive state in which power for front wheel drive is taken from the front wheel driving transmission shaft  20  at a speed synchronized with a rear wheel driving speed. When the shift gear G 8  is shifted rearward to disengage from the output gear G 7 , the front wheels  8  are no longer driven and a rear, two wheel driving state is provided to drive only the rear wheels  6 .  
         [0035]     On the other hand, as shown in  FIG. 2 , the clutch housing  2  includes a dry type clutch chamber “a” for accommodating the main clutch C 1 , and a wet type (oil bath lubrication type) change speed chamber “b” isolated from the chamber “a”. The change speed chamber “b” houses a front wheel change speed mechanism  21  for receiving the front wheel driving power taken forward from the front wheel driving transmission shaft  20 . The front wheel change speed mechanism  21  includes an input shaft  23  coaxially coupled to the front wheel driving transmission shaft  20  through an intermediate shaft  22 , and a transmission shaft  24  extending parallel to the input shaft  23 . The transmission shaft  24  has a shift clutch C 2  mounted thereon and operable to rotate the transmission shaft  24  at two, high and low speeds. The power is then transmitted through gears to a front wheel drive shaft  26  disposed at a lower end of the clutch housing  2 . The power taken forward from the front wheel drive shaft  26  at the two, high and low speeds is transmitted to the front axle case  9 .  
         [0036]     The input shaft  23  has a large diameter gear G 9  and a small diameter gear G 10 . The transmission shaft  24  has a small diameter idle gear G 11  and a large diameter idle gear G 12  in constant mesh with these gears G 9  and G 10 . The shift clutch C 2  mounted on the transmission shaft  24 , as shown in  FIG. 5 , includes a frictional transmission portion  29  of the multi-disk type disposed between a clutch drum  27  fixed to the transmission shaft  24  and a splined boss  28  formed integral with the small diameter idle gear G 11 . The clutch drum  27  contains a piston member  30  displaceable by pressure oil supplied and drained through an oil passage formed in the transmission shaft  24  and by a spring  31  mounted in the clutch drum  27 , thereby placing the friction transmission portion  29  in a pressure contact state and canceling the pressure contact state to engage and disengage the clutch C 2 .  
         [0037]     A shift member  32  is shiftably mounted on a boss portion of the clutch drum  27 , and rigidly connected to the piston member  30  through connecting pins  33  penetrating the clutch drum  27 . Thus, the shift member  32  is shifted with movement of the piston member  30 . When the pressure oil supply is stopped, as shown in  FIG. 5 , the piston member  30  is displaced leftward in the figure by the inner spring  31 , to place the shift clutch C 2  in “off” state. At the same time, the shift member  32  connected to the piston member  30  meshes with a side of the large diameter idle gear G 12 . Power is transmitted from the input shaft  23  to the transmission shaft  24  at reduced speed through the small diameter gear G 10 , large diameter idle gear G 12 , shift member  32  and clutch drum  27 . Then, the power is taken from the forward end of the transmission shaft  24 , and transmitted to the front axle case  9  through the front wheel driving shaft  26 . In this case, the front wheels  8  are driven at a peripheral velocity equivalent to (or slightly faster than) a rear wheel peripheral velocity, thereby to provide a standard four wheel drive mode.  
         [0038]     When pressure oil is supplied, as shown in  FIG. 6 , the piston member  30  is moved against the force of inner spring  31 , rightward in the figure, to place the friction transmission portion  29  in the pressure contact state, and thus to place the shift clutch C 2  in “on” state. At the same time, the shift member  32  connected to the piston member  30  is moved out of mesh with the large diameter idle gear G 12 . Power is transmitted from the input shaft  23  to the transmission shaft  24  at increased speed through the large diameter gear G 9 , small diameter idle gear G 11 , friction transmission portion  29  and clutch drum  27 . Then, the power is transmitted to the front axle case  9  through the front wheel driving shaft  26 . In this case, the front wheels  8  are driven at about twice the rear wheel peripheral velocity, thereby to provide a front wheel accelerating drive mode.  
         [0039]     As shown in the hydraulic circuit diagram of  FIG. 7 , the pressure oil supplying and draining passage for the shift clutch C 2  has, arranged in series, a front wheel control valve V 1  switchable as interlocked with steering of the front wheels  8 , an automatic change speed selector valve V 2  for turning on and off an automatic change speed of the front wheels  8 , and a check valve V 3  switchable as interlocked with shifting of the auxiliary change speed gear mechanism  19 . A hydraulic pump OP driven by the engine  1  delivers pressure oil through a power steering unit  87  and an oil cooler  88  to a hydraulic circuit “f” for front wheel change speed, Return oil from the hydraulic circuit “f” for front wheel change speed is supplied to a charge circuit “g” for the hydrostatic stepless transmission  12 .  
         [0040]     As shown in  FIGS. 6 and 7 , the front wheel control valve V 1 , automatic change speed selector valve V 2  and check valve V 3  are in the form of rotary valves, respectively, These valves V 1 , V 2 , and V 3  are assembled to a single valve casing  90  connected to the rear of clutch housing  2 . While the front wheel control valve V 1  and check valve V 3  are arranged in parallel, the automatic change speed selector valve V 2  located between the valves V 1  and V 3  has a spool axis extending perpendicular to the spool axes of the other valves V 1  and V 3 .  
         [0041]     The front wheel control valve V 1  is mechanically interlocked to a steering mechanism  91  of the front wheels  8 . When the front wheels  8  are in a straight running state, the control valve V 1  shuts the oil passage. When the front wheels  8  are steered in excess of a predetermined angle (e.g. 35 degrees) left or right from the straight running state, the front wheel control valve V 1  is turned to open the oil passage. The automatic change speed selector valve V 2  is linked to a change lever  92 , to open the oil passage when the change lever  92  is in an automatic change speed “on” position, and shut the oil passage when the change lever  92  is in an automatic change speed “off” position. The check valve V 3  is linked to an auxiliary shift lever  93  for switching the auxiliary change speed gear mechanism  19  which provides three propelling speeds. The oil passage is opened when the auxiliary change speed gear mechanism  19  is shifted for the “low speed” or “intermediate speed”. The oil passage is shut when the auxiliary change speed gear mechanism  19  is shifted for the “high speed”.  
         [0042]     Thus, only when the automatic change speed “on” position is selected for the automatic change speed selector valve V 2  to open the oil passage, and the auxiliary change speed gear mechanism  19  is shifted for the “low speed” or “intermediate speed” with the check valve V 3  opening the oil passage, the front wheel control valve V 1  is switched as interlocked to a steering operation exceeding the predetermined angle of the front wheels  8 , to supply the pressure oil to the shift clutch  25 . Then, the front wheels  8  are driven in acceleration for the tractor to make a smooth, small turn. When the auxiliary change speed gear mechanism  19  is shifted for “high speed” even though the automatic change speed “on” position is selected for the automatic change speed selector valve V 2 , the automatic front wheel acceleration is not carried out irrespective of a steering operation exceeding the predetermined angle of the front wheels  8 . When the automatic change speed “off” position is selected for the automatic change speed selector valve V 2  to close the oil passage, naturally the automatic front wheel acceleration never takes place in response to a front wheel steering operation.  
         [0043]     A PTO transmission system will be described next.  
         [0044]     The rear end of the input shaft  13  extending through and supported by the upper position of the main transmission  12  is aligned with a PTO transmission shaft  35  extending through and supported by the intermediate partition wall  3   a.  A PTO clutch C 3  of the hydraulically operable multi-disk type is interposed between the input shaft  13  and PTO transmission shaft  35 .  
         [0045]     As shown in  FIG. 8 , the PTO clutch C 3  includes a clutch drum  37  splined to the rear end of the input shaft  13 , a shift member  38  shiftably splined to the PTO transmission shaft  35 , a clutch sleeve  39  shiftably splined to the shift member  38 , a friction transmission portion  40  of the multi-disk type interposed between the clutch drum  37  and clutch sleeve  39 , a clutch-operating piston member  41  contained in the clutch drum  37 , and an inner spring  42  for biasing the piston member  41  in a friction release direction. Pressure oil is supplied through an oil passage “c” formed in the PTO transmission shaft  35  to displace the piston member  41  against the force of spring  42  rightward in  FIG. 8 . This places the friction transmission portion  40  in a pressure contact state, and thus a “clutch on” state. When the pressure oil supply is stopped, the piston member  41  is displaced by the sprint  42  leftward in  FIG. 8 . This releases the friction transmission portion  40  from the pressure contact state, and thus a “clutch off” state.  
         [0046]     A switching valve V 4  for PTO clutch operation is connected to the upper surface of the transmission case  3  for applying and stopping a control pressure to the oil passage “c” in the PTO transmission shaft  35 . The switching valve V 4  is operable by a PTO clutch lever CL disposed, to be pivotable fore and aft, at a left side of a driver&#39;s seat  61 .  
         [0047]     As shown in  FIGS. 13 and 14 , the PTO clutch lever CL has an operating path defining a “clutch on” position in a rearward region thereof, and a “clutch off” position in a forward region. When a “clutch on” state is selected, power transmitted to the clutch sleeve  39  is transmitted to the PTO transmission shaft  35  through the shift member  38 , and transmitted to a position rearward of the differential case  5  through an intermediate transmission shaft  43  connected coaxially to the rear end of the PTO transmission shaft  35 . The power is greatly decelerated by gears G 13  and G 14  arranged rearwardly of the differential case  5 , to be outputted from the rear PTO shaft  7 .  
         [0048]     A PTO brake mechanism  45  is disposed rearwardly of the PTO clutch C 3 , which is interlocked to the “clutch off” operation to stop inertial rotation of the downstream transmission elements. The PTO brake mechanism  45  includes a friction plate  46  splined to the clutch sleeve  39 , a seat member  47  fixed to an inner wall of the transmission case  3 , and a braking plate  48  unrotatably supported inside the transmission case  3 . When the PTO clutch C 3  is disengaged to have the piston member  41  moved leftward in the drawings by the biasing force of inner spring  42 , the clutch sleeve  39  moves in the same direction with the piston member  41 . Then, the friction plate  46  is pinched between the seat member  47  and braking plate  48  to brake the clutch sleeve  39 .  
         [0049]     As shown in  FIG. 3 , the transmission case  3  has a mid-PTO case  51  connected to an undersurface thereof forwardly of the intermediate partition wall  3   a.  The mid-PTO case  51  supports a mid-PTO shaft  50  projecting forward therefrom. The front portion forward of the intermediate partition wall  3   a  of the transmission case  3  houses a mid-PTO transmission mechanism  52  for gear-interlocking the PTO transmission system and the mid-PTO shaft  50 , and a PTO mode selecting device  53  for switching between states of power takeoff from the rear PTO shaft  7  and from the mid-PTO shaft  50 .  
         [0050]     The mid-PTO transmission mechanism  52  includes a power takeoff gear G 15  loosely fitted on a rear portion of the PTO transmission shaft  35 , and a gear G 16  formed integral with the mid-PTO shaft  50 , the gears G 15  and G 16  being interlocked through relay gears G 17 , G 18  and G 19 . The relay gear G 17  is loosely fitted on the front wheel driving transmission shaft  20 . The relay gear G 18  is loosely fitted on the propelling transmission shaft  17 . The relay gear G 19  is loosely fitted on a support shaft  54  mounted on a bottom wall of the transmission case  3 .  
         [0051]     The PTO mode selecting device  53  is operable by shifting the shift member  38  forward and backward to select a mode for transmitting power only to the rear PTO shaft  7 , a mode for transmitting power to both the rear PTO shaft  7  and mid-PTO shaft  50 , or a mode for transmitting power only to the mid-PTO shaft  50 . When the shift member  38  is shifted to a foremost position, as shown in  FIG. 9 , the shift member  38  is meshed only with splines  35   a  of the PTO transmission shaft  35 . Then, the power transmitted to the shift member  38  through the PTO clutch C 3  is transmitted only to the rear PTO shaft  7  through the intermediate transmission shaft  43 .  
         [0052]     When the shift member  38  is shifted to a fore and aft intermediate position, as shown in  FIG. 8 , the shift member  38  is meshed with the splines  35   a  of the PTO transmission shaft  35  and splined to a boss of the power takeoff gear G 15 . Then, the power transmitted to the shift member  38  through the PTO clutch C 3  is transmitted to the rear PTO shaft  7  through the intermediate transmission shaft  43 , and also to the mid-PTO shaft  50  through the mid-PTO transmission mechanism  52 .  
         [0053]     When the shift member  38  is shifted to a rearmost position, as shown in  FIG. 10 , the shift member  38  is splined only to the boss of the power takeoff gear G 15 . Then, the power transmitted to the shift member  38  through the PTO clutch C 3  is transmitted only to the mid-PTO shaft  50  through the mid-PTO transmission mechanism  52 .  
         [0054]     A shaft coupling sleeve  55  extends between and is splined to the PTO transmission shaft  35  and intermediate transmission shaft  43 . When the PTO mode selecting device  53  selects the transmission mode for driving only the mid-PTO shaft  50 , the shaft coupling sleeve  55  acts as a PTO brake B for preventing inertial rotation of the rear PTO shaft  7  in free state.  
         [0055]     The shaft coupling sleeve  55  is splined to be shiftable back and forth, and has a control system linked so that the shaft coupling sleeve  55  may be shifted in a reverse direction synchronously with the PTO mode selecting shift member  38 . Specifically, as shown in  FIGS. 11 and 12 , a side wall of the transmission case  3  is penetrated by, and supports, a control shaft  56  having an eccentric operating pin  56   a  for engaging the shift member  38 , and a control shaft  57  having a control arm  57   a  for engaging the shaft coupling sleeve  55 . The control shaft  56  has an operating pin  56   b  disposed at an outer end thereof and interlocked through a rod  59  to a PTO mode select lever  58  pivotable back and forth about an axis “p”. The control shaft  57  has a connecting lever  57   b  extending from an outer end thereof and interlocked by a slot to the operating pin  56   b.  The shift member  38  and shaft coupling sleeve  55  are shifted in opposite directions to each other by a fore and aft operation of the PTO mode select lever  58 .  
         [0056]     Thus, when the PTO mode select lever  58  is operated to a rearmost position, the shift member  38  is shifted to the foremost position to select the transmission mode for driving only the rear PTO shaft  7 . When the PTO mode select lever  58  is operated to a fore and aft intermediate position, the shift member  38  is shifted to the fore and aft intermediate position to select the transmission mode for driving both the rear PTO shaft  7  and mid-PTO shaft  50 . In the above state, the shaft coupling sleeve  55  is in the rearmost position or fore and aft intermediate position in its shifting range. At this time, the shaft coupling sleeve  55  functions as a mere shaft coupling. When the PTO mode select lever  58  is operated to a foremost position, the shift member  38  is shifted to the rearmost position to select the transmission mode for driving only the mid-PTO shaft  50 . With the rearward shift of the shift member  38 , the shaft coupling sleeve  55  moves forward whereupon an engaging pawl  55   a  at the forward end of the shaft coupling sleeve  55  engages a rib  60  formed on a rear surface of the intermediate partition wall  3   a  in the transmission case  3 . As a result, the PTO brake B functions to stop rotation of the PTO transmission shaft  35  and intermediate transmission shaft  43  in a state of free rotation.  
         [0057]     As shown in  FIGS. 13 and 14 , the PTO mode select lever  58  is disposed at the left side of the driver&#39;s seat  61  to be pivotable back and forth. The PTO mode select lever  58  has an operating path formed directly rearwardly of the operating path of the PTO clutch lever CL. That is, the operating path of the PTO mode select lever  58  is substantially aligned with the operating path of the PTO clutch lever CL. Laterally outwardly of the PTO mode select lever  58  and PTO clutch lever CL, the auxiliary shift lever  93  noted hereinbefore is disposed to be pivotable back and forth.  
         [0058]     As shown in  FIG. 1 , lever lengths are selected so that the PTO clutch lever CL has a grip CLa thereof higher than a grip  58   a  of the PTO mode select lever  58 . Thus, the driver&#39;s arm operating the PTO clutch lever CL can easily move clear of the PTO mode select lever  58 .  
         [0059]     Arranged above and rearwardly of the differential case  5  are lift arms  95  for raising and lowering a working implement, and a lift cylinder  96  for driving the lift arms  95 . The lift cylinder  96  is controlled by a position control valve, not shown, linked to a position lever  97  disposed at the right side the driver&#39;s seat  61 . As shown in  FIG. 15 , the position lever  97  is retainable in a selected control position by a frictional force of a plate spring  98  provided on a lever fulcrum. Thus, the lift arms  95  may be raised or lowered to and stopped at a height corresponding to a position in which the position lever  97  is retained. The plate spring  98  has a characteristic of spring load in relation to the amount of compression, which, as shown in  FIG. 16 , includes a spring load stable region in an intermediate part of the deformation range. The plate spring  98  is assembled in this stable spring load condition, so that its frictional retaining function is not seriously affected by minor variations in the amount of compression due to a clamping error occurring in time of assembly.  
         [0060]     FIGS.  18 ,  19 (A) and  19 (B) show an operating guide for the PTO clutch lever CL that switches the PTO clutch control valve, and for the PTO mode select lever  58 .  
         [0061]     The PTO clutch lever CL and PTO mode select lever  58  are arranged in fore and aft positions close to each other at the left side of the driver&#39;s seat  61 . These levers CL and  58  extend through a lever guide  63  attached to a fender  62 . The PTO clutch lever CL is mechanically interlocked to the valve V 4  through a link mechanism not shown, such that a forward operation of the PTO clutch lever CL provides a “clutch on” state, and a rearward operation thereof provides a “clutch off” state. Further, a restricting device  64  is provided between the PTO clutch lever CL and PTO mode select lever  58  for restricting operation of the PTO mode select lever  58 .  
         [0062]     The restricting device  64  is disposed adjacent the undersurface of the lever guide  63  and, as shown in  FIG. 20 , includes a bracket  65  mounted inside the lever guide  63  and fixedly screwed thereto from below, and an elongate restricting element  66 , which is an example of restricting member, pivotally supported by the bracket  65  to be swingable about a vertical fulcrum “m”. The fulcrum “m” is located in an intermediate position between a guide groove  67  of the PTO clutch lever CL and a guide groove  68  of the PTO mode select lever  58 . The restricting element  66  has a control portion  66   a  extending forward from the fulcrum “m”, and a restricting portion  66   b  extending rearward from the fulcrum “m”. Further, the restricting element  66  is biased to swing in one direction (i.e. counterclockwise in  FIG. 19 ) by a torsion spring  69  mounted on the fulcrum “m”.  
         [0063]     The control portion  66   a  of the restricting element  66  overlaps a clutch-off region of the guide groove  67  of the PTO clutch lever CL, and has an inclined cam  70  formed on a side edge thereof for contacting and cooperating with the PTO clutch lever CL operated to the “clutch off” position. The restricting portion  66   b  of the restricting element  66  is formed to have a length for overlapping a “mid-PTO drive” position and a “mid-/rear PTO drive” position in the guide groove  68  of the PTO mode select lever  58 . The restricting portion  66   b  has, formed along a side edge thereof, a recess  71  for receiving and retaining the PTO mode select lever  58  in the “mid-PTO drive” position, and a recess  72  for receiving and retaining the PTO mode select lever  58  in the “mid-/rear PTO drive” position.  
         [0064]     With the above restricting device  64 , when the PTO clutch lever CL is operated to the forward “clutch on” position, as shown in  FIG. 19  (B), the restricting element  66  is in a free state and is swung by the biasing force into contact with a stopper  65   a  bent from the bracket  65 , to be retained in a fore and aft posture. At this time, the restricting portion  66   b  of the restricting element  66  overlaps the guide groove  68  of the PTO mode select lever  58 . The PTO mode select lever  58  in the “mid-PTO drive” position or “mid-/rear PTO drive” position is located in the recess  71  or recess  72 , to be inoperable to different positions. The PTO mode select lever  58  in the “rear PTO drive” position is prevented from operating forward by the rear end of the restricting element  66 .  
         [0065]     When the PTO clutch lever CL is operated to the rearward “clutch off” position, as shown in  FIG. 19 (A), the inclined cam  70  on the control portion  66   a  of the restricting element  66  is contacted and pressed by the PTO clutch lever CL, whereby the restricting element  66  is forcibly swung clockwise against the force of torsion spring  69 . As a result, the restricting portion  66   b  is retracted leftward from the guide groove  68 . The PTO mode select lever  58  can now be operated backward or forward as desired.  
         [0066]     The restricting element  66  of the restricting device  64  is formed of a glossy metal plate material (e.g. plated sheet steel or stainless steel plate) to be clearly visible through the guide grooves  67  and  68 . Thus, the operator can easily make a visual or auditory recognition of a functional state of the restricting device  64  by a position of the restricting element  66 , or by a metallic sound produced in time of restricting operation. Consequently, when a selecting operation by the PTO mode select lever  58  becomes impossible, the operator is unlikely to operate the select lever  58  forcibly, thereby to damage the restricting device  64  or bend the PTO mode select lever  58 .  
         [0067]     The bracket  65  has guide pieces  65   b  and  65   c  bent to project downward from positions forwardly and rearwardly of the fulcrum “m”. These guide pieces  65   b  and  65   c  have lower ends thereof shaped to make a sliding contact with the upper surface of the restricting element  66 , thereby to guide the latter to be retained stably in place.  
       Other Embodiments  
       [0068]     (1) Where there is an allowance of space laterally of the driver&#39;s seat  61 , as shown in  FIG. 17 , the operating paths of the PTO clutch lever CL and PTO mode select lever  58  may be arranged in fore and aft positions slightly staggered transversely from each other. The PTO clutch lever CL and PTO mode select lever  58  may be arranged at the right side of the driver&#39;s seat  61 .  
         [0069]     (2) The PTO clutch C 3  is not limited to the hydraulically operable multidisk clutch, but may be a manually operable multidisk clutch or a claw clutch.  
         [0070]     (3) The restricting device  64  may be provided between the link mechanism interlocking the PTO clutch lever CL and valve V 4 , and the switching link mechanism of the PTO mode select lever  58 .  
         [0071]     (4) The restricting device  64  may be constructed electrically operable. For example, the control positions of the PTO clutch lever CL are electrically detected with a switch or the like. A lock member is provided to act on an appropriate part of the PTO mode select lever  58  or its control link mechanism. Upon detection of the PTO clutch lever CL in the “clutch on” position, the lock member is held in a lever locking position by means of a spring or the like. Upon detection of the PTO clutch lever CL in the “clutch off” position, a potential solenoid is operated to switch the lock member to a lock releasing position.