Abstract:
To provide a working vehicle with a simple body structure, an HST case containing a hydraulic stepless transmission is disposed between an engine adjacent one end in a fore and aft direction of a vehicle body, and a propelling transmission case disposed adjacent the other end in the fore and aft direction. The HST case, with the engine and propelling transmission case, forms the vehicle body. With this construction, a driving deck is located at a relatively low level so that the driver may board and alight from the deck with ease. Despite the low level of the deck, the bottom of the vehicle body is at a relatively high level to be free from contact with projections on unleveled terrain. Frame strength may be increased where the HST case is connected between a main clutch housing connected to the rear of the engine and the propelling transmission case.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a working vehicle having an engine disposed in a forward position of a vehicle body, and a propelling transmission disposed in a rearward position of the vehicle body for receiving engine output transmitted through a hydraulic stepless transmission. 
     2. Description of the Related Art 
     As an example of conventional working vehicles as noted above, an agricultural tractor is disclosed in Japanese Patent Laying-Open Publication H7-329587. This tractor has a body frame formed of an engine, a front transmission integrated with the rear of the engine, a transmission frame coupled at a forward end thereof to the front transmission, and a rear transmission coupled to the rear end of the transmission frame. A hydraulic stepless transmission is mounted in the transmission frame for changing speed of engine output and transmitting it to the rear transmission. 
     The above prior art vehicle has a complicated construction since the body frame and transmissions must be formed separately. This vehicle has a further disadvantage that an upper portion of the vehicle body is at a high level above the ground while the bottom of the vehicle body is at a low level above the ground. 
     Other conventional examples of working vehicles are disclosed in U.S. patent Ser. No. 4,997,760 and Japanese Patent Laying-Open Publication S64-16436. In these working vehicles, a stepless transmission is operable by a change speed pedal. The driver may operate the stepless transmission easily with a foot to control the running speed of the vehicle. In these working vehicles, the change speed pedal and a control part of the transmission are relatively remote from each other longitudinally of the vehicle body. Thus, where the change speed pedal and transmission are connected to each other through an interlocking mechanism (pivotal links and rods, etc.), friction and flexibility of connecting parts in the interlocking mechanism result in increased operational resistance and play, which impair response and tend to worsen operability of the vehicle. Besides, the change speed pedal is located at a low level for the level at which the transmission is disposed, and is low relative to the driver&#39;s seat. Consequently, when the driver depresses the change speed pedal, an excessive force acts on the driver&#39;s foot at a relatively early stage of operation. This results in inconveniences of a reduced shifting range and the like which tend to worsen operability. 
     As a further example of conventional working vehicles, a tractor is disclosed in Japanese Patent Laying-Open Publication H7-32897. In this tractor, a change speed pedal is supported by a support bracket fixed to a body frame. The change speed pedal is coupled to a trunnion (control part) of a stepless transmission through a link and so on. Running speed may be changed by controlling the stepless transmission with the change speed pedal. In many tractors, the driving deck is supported by the body frame through rubber cushions. In the tractors having a change speed pedal supported by the body frame as in this conventional tractor, the driver&#39;s foot attempting to operate the change speed pedal may inadvertently deviate therefrom when a relative displacement due to running vibration or the like occurs between the driving deck above the rubber cushions and the body frame below the rubber cushions. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a working vehicle having a simple construction regarding a body frame and transmissions while enabling easy shifting operations. 
     Another object of this invention is to provide a working vehicle having a change speed pedal of excellent operability for effecting change speed operations. 
     A further object of this invention is to provide a relatively simple speed control structure for allowing a stepless transmission to be controllable by a change speed pedal with excellent operability even for a working vehicle having a driving deck supported by a body frame through rubber cushions or the like. 
     The above objects are fulfilled, according to this invention, by a working vehicle comprising: 
     an engine disposed adjacent one end in a fore and aft direction of a vehicle body; 
     a propelling transmission case disposed adjacent the other end in the fore and aft direction of the vehicle body; and 
     an HST case disposed between the engine and the propelling transmission case; 
     the HST case housing a hydraulic stepless transmission having a hydraulic pump and a hydraulic motor for changing speed of engine output and transmitting the engine output to the propelling transmission in the propelling transmission case; 
     the HST case defining an oil chamber accommodating the hydraulic pump and the hydraulic motor; 
     wherein the engine, the propelling transmission case and the HST case constitute a body frame. 
     According to the above construction, the stepless transmission case is disposed between the engine and the propelling transmission case to form the body frame in combination with the engine and the propelling transmission case. The body frame has a simplified construction with the stepless transmission case used for forming the body frame. Moreover, a driving deck is located at a relatively low level so that the driver may board and alight from the deck with ease. Despite the low level of the deck, the bottom of the vehicle body is at a relatively high level to be free from contact with projections on unleveled terrain. Thus, the vehicle has an improved running performance. 
     The above working vehicle may further comprise a main clutch housing connected to the rear of the engine, wherein the HST case is connected between the main clutch housing and the propelling transmission case to increase frame strength. 
     To position the upper surface of the HST case in a reduced level and the bottom thereof in an elevated level, the hydraulic pump and the hydraulic motor may be arranged in the HST case transversely instead of vertically of the vehicle body, or a control device (a servo cylinder and a servo valve) for varying a swash plate angle of the hydraulic pump may be disposed on a side surface of the HST case. 
     Further, the hydraulic pump may advantageously have an intake port and a drain port arranged in a direction relative to the vehicle body different from a direction of arrangement of an intake port and a drain port of the hydraulic motor. For example, the ports of one may be arranged vertically while the ports of the other are arranged transversely of the vehicle body. Then, an oil line between the intake port of the hydraulic pump and the drain port of the hydraulic motor, and an oil line between the drain port of the hydraulic pump and the intake port of the hydraulic motor, may include minimum bends or bypasses to avoid a complicated layout. The two oil lines have a short and simple configuration. 
     In a preferred embodiment of the invention, the hydraulic stepless transmission is disposed adjacent and rearwardly of the main clutch, the hydraulic stepless transmission being operable by a change speed pedal disposed in a position above the hydraulic stepless transmission and where the hydraulic stepless transmission and the change speed pedal overlap each other in plan view. 
     Generally, the change speed pedal, if disposed adjacent the main clutch, is in an appropriate positional relationship with a driver&#39;s seat, to be easily operable without applying an excessive force to the driver&#39;s foot and through an increased depressing stroke. Where the hydraulic stepless transmission is disposed adjacent and rearwardly of the main clutch, the change speed pedal may also be disposed adjacent the main clutch. Besides, where the change speed pedal is operatively connected to the hydraulic stepless transmission through an interlocking mechanism, the interlocking mechanism may be small and light and free from excessive operational resistance and play at connections. This facilitates a control operation using the change speed pedal, and assures an improved response to the control operation. 
     According to this invention, a power branching mechanism may be disposed between the main clutch and the hydraulic stepless transmission for dividing power from the engine to an input of the hydrostatic stepless transmission and to an implement driving transmission disposed in a rearward portion of the vehicle body. With this power branching mechanism, the implement driving transmission receives the power without speed variation when the stepless transmission changes running speed. Moreover, since the power branching mechanism is disposed between the main clutch and the hydraulic stepless transmission, the implement driving transmission receives the power without speed variation despite variations in running speed while the weight of the power branching mechanism is offset forwardly of the vehicle body. Thus, when a working implement is connected to the rear of the vehicle body, the weight of the power branching mechanism is used so that a reduced number of balancing weights is required to secure a front and rear weight balance. This results in a reduced weight of the working vehicle. 
     In a preferred embodiment of the invention, the change speed pedal is pivotably supported on the driving deck. With this construction, the change speed pedal moves with the driving deck relative to the body frame when running vibrations occur with a tractor in which the driving deck is supported on the body frame through rubber cushions. Even when a relative displacement occurs between the driving deck and body frame, a relative displacement hardly occurs between the pedal and deck. Consequently, pedal action is stabilized. 
     Where the change speed pedal is operatively connected to the control device of the stepless transmission through the interlocking mechanism, a relative displacement between the driving deck and body frame is absorbed by movement of pivotal links and the like forming the interlocking mechanism. Thus, an inadvertent change speed operation is unlikely to be caused for the transmission. Where a neutral restoring device of relatively simple structure such as a spring is provided for both of the change speed pedal and stepless transmission, the change speed pedal and transmission smoothly return to neutral positions when the change speed pedal is released from a depressed position. Thus, a relatively inexpensive speed control structure is obtained which responds to a pedal operation with high precision, neither excessively nor insufficiently. 
     Other features, functions, effects and advantages of the present invention will be appreciated upon reading the following description with reference to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a side elevation of an agricultural tractor shown as one example of working vehicles according to this invention; 
     FIG. 2 is a side view of a body frame; 
     FIG. 3 is a schematic view of an engine power transmission system; 
     FIG. 4 is a sectional view of a main clutch and a power branching mechanism; 
     FIG. 5 is a sectional view of a propelling stepless transmission; 
     FIG. 6 is a sectional view of a hydraulic pump forming part of the propelling stepless transmission; 
     FIG. 7 is a sectional view of oil lines for driving the stepless transmission; 
     FIG. 8 is a sectional view of a servo valve controller; 
     FIG. 9 is a sectional view of a servo valve; 
     FIG. 10 is a side view of an interlocking mechanism between a change speed pedal and the stepless transmission; 
     FIG. 11 is a sectional view of a driving deck; 
     FIG. 12 is a sectional view of a speed retainer; 
     FIG. 13 is a side view of a cruising device; 
     FIG. 14 is a plan view of brake pedals; 
     FIG. 15 is a plan view of the change speed pedal; 
     FIG. 16 is an explanatory view of operation of an interlock regulating mechanism; 
     FIG. 17 is a side view corresponding to FIG.  10  and showing an interlocking mechanism between a change speed pedal and a stepless transmission in another embodiment; 
     FIG. 18 is a side view of an interlocking mechanism between a speed retainer and a cruise lever; 
     FIG. 19 is an explanatory view showing control positions of the cruise lever; 
     FIG. 20 is a sectional view of the cruise lever; 
     FIG. 21 is an explanatory view of operation of a cruise regulating mechanism; and 
     FIG. 22 is a side view corresponding to FIG.  2  and showing a modified body frame. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of this invention will be described hereinafter. In the following embodiment, the invention is applied to an agricultural tractor which is one example of working vehicles. 
     The agricultural tractor shown in FIG. 1 includes right and left front drive wheels  1  and right and left rear drive wheels  2 , a motor section having an engine E disposed in a front position of a vehicle body, and a driver&#39;s section having a steering wheel  3  for steering the front wheels  1  and a driver&#39;s seat  4 . In a rearward portion of the vehicle body are a transmission case  5 , lift arms  6  for raising and lowering a varied working implement coupled to the vehicle body, and a PTO shaft  7  for transmitting power to the working implement coupled to the vehicle body. For instance, the working implement may be a plow so that the tractor acts as a riding type cultivator. 
     As shown in FIGS. 1 and 2, a body frame F of this tractor includes the engine E, front frames  8  extending forward from opposite lower side positions of engine E, a flywheel housing  9  disposed rearwardly of engine E, a main clutch housing  10  bolted to the rear end of flywheel housing  9 , an HST case  21  having a forward end thereof coupled to the rear end of main clutch housing  10 , and the transmission case  5  having a forward end thereof coupled to the rear end of HST case  21 . 
     The transmission case  5  includes a main transmission case body  5   a  having a forward end thereof coupled to HST case  21 , and a differential case portion  5   b  having a forward end thereof bolted to the rear end of main transmission case body  5   a.    
     As shown in FIG. 3, a front wheel transmission case  11  supported by the right and left front frames  8  contains a front differential  12 . The differential case portion  5   b  contains a rear differential  13 . The flywheel housing  9  contains a flywheel  14  acting as an engine output member. The main clutch housing  10  contains a main clutch  15 . The forward end of a rotary shaft  16  is splined to the flywheel  14 . A power branching mechanism  17  is disposed between the main clutch  15  and HST case  21  for dividing power of engine E into propelling power transmitted to the front and rear wheels  1  and  2 , and power transmitted to the working implement through the PTO shaft  7 . As shown in FIG. 4, a case part  10   a  is bolted to a front surface of a rear portion of main clutch housing  10 . A transmission case part  10   b  is in the rear portion of main clutch housing  10 . The power branching mechanism  17  is disposed in the case parts  10   a  and  10   b . Further, a main transmission  20  is disposed in HST case  21 , and an auxiliary transmission  40  (propelling transmission) in the transmission case  5 . 
     With the above transmission structure, torque output of engine E divided by the power branching mechanism  17  as propelling power is transmitted to the front and rear differentials  12  and  13 . The front and rear wheels  1  and  2  are thereby driven, so that the tractor functions as a self-propelled vehicle. 
     Specifically, torque of the flywheel  14  is transmitted to the power branching mechanism  17  through the main clutch  15  and rotary shaft  16 . The power branching mechanism  17  has a first output gear  17   d  for transmitting torque to an input shaft  22  of the main transmission  20 . The main transmission  20  has an output shaft  23  for transmitting torque through a gear mechanism  18  to an input shaft  41  of the auxiliary transmission  40 . The auxiliary transmission  40  has an output shaft  42  for transmitting torque to the rear differential  13  through an output gear  43  formed integral with the rear end of the output shaft  42 . The output shaft  42  transmits the torque also to the front differential  12  through a front wheel driving output gear  44  mounted on the output shaft  42  to be rotatable therewith, and a front wheel transmission shaft  19  having a rear end thereof interlocked to the output gear  44  through a gearing. 
     The auxiliary transmission  40  receives the torque from the main transmission  20 , and transmits it in three speeds to the front and rear wheels  1  and  2 . The auxiliary transmission  40  includes a transmission shaft  41   a  coupled to the input shaft  41  to be rotatable therewith, a first shift gear  45  splined to the transmission shaft  41   a  to be rotatable therewith and slidable thereon, a second shift gear  46  splined to the output shaft  42  to be rotatable therewith and slidable thereon, a gear  47  relatively rotatably mounted on the transmission shaft  41   a , a gear  48  relatively rotatably mounted on the output shaft  42 , and a gear  49  formed integral with the transmission shaft  41   a . In this construction, the first shift gear  45  is selectively engageable with the gear  47  and gear  48 , while the second shift gear  46  is selectively engageable with the gear  49  and gear  48 . As a result, the torque of the input shaft  41  is changed into three speeds to be outputted from the output shaft  42 . 
     On the other hand, the other part of power branching from the power branching mechanism  17  is transmitted, through an implement driving transmission  50  disposed in the transmission case  5 , to the PTO shaft  7  rotatably supported at the rear end of the transmission case  5 . 
     More particularly, the power branching mechanism  17 , as shown in FIG. 4, includes a first input gear  17   a  formed integral with the rear end of a tubular output shaft  16   a  of main clutch  15  to be rotatable therewith, a first transmission gear  17   b  meshed with the first input gear  17   a , a second transmission gear  17   c  having a shaft portion thereof splined to the first transmission gear  17   b  to be rotatable therewith, the above-mentioned first output gear  17   d  meshed with the second transmission gear  17   c , a second input gear  17   e  formed integral with the rear end of the rotary shaft  16  relatively rotatably extending through the tubular output shaft  15   a , and a second output gear  17   f  meshed with the second input gear  17   e . The first output gear  17   d  is splined to the input shaft  22  of the main transmission  20  to be rotatable therewith. The second output gear  17   f  is formed integral with an input shaft  51  of the implement driving transmission  50  to be rotatable therewith. 
     The power branching mechanism  17  divides the torque output of engine E into a line connectable and disconnectable by the main clutch  15  and a line through the rotary shaft  16  not connectable and disconnectable. The engine output through the connectable and disconnectable line is transmitted to the front and rear wheels  1  and  2  by way of the input shaft  22  of the main transmission  20 . On the other hand, the engine output through the line not connectable and disconnectable is transmitted to the PTO shaft  7  by way of the input shaft  51  of the implement driving transmission  50 . The implement driving transmission  50  further includes a multidisk clutch  52  engageable by pressure oil supply, an output shaft  53  of the clutch  52 , and a rotary shaft  55  having one end thereof coupled to the output shaft  53  through a gear mechanism  54 , and the other end coupled to the PTO shaft  7  through a coupling to be rotatable therewith. The power branching mechanism  17  divides the engine output into the two lines as noted above. The torque output of engine E is transmitted to the implement driving transmission  50  independently of the main transmission  20  and auxiliary transmission  40  on the propelling line. Consequently, the implement driving power is not variable by a shifting operation of the main transmission  20  or auxiliary transmission  40 . The power transmitted to the implement driving transmission  50  is connected to and disconnected from the PTO shaft  7  by the multidisk clutch  52 . 
     As shown in FIGS. 5 and 6, the main transmission  20  includes a variable capacity hydraulic motor M and a fixed capacity hydraulic pump P. The hydraulic pump P is driven by the input shaft  22 . The hydraulic motor M is driven by pressure oil from the hydraulic pump P, and drives the output shaft  23  of the main transmission  20 . Both the hydraulic pump P and hydraulic motor M are disposed in the HST case  21 . The main transmission  20  is constructed as a hydraulic stepless transmission. The main transmission  20  is located adjacent the rear end of the main clutch  15 . The hydraulic pump P and hydraulic motor M convert the engine output transmitted to the input shaft  22  into forward drive or backward drive, steplessly changes speed of the forward drive or backward drive, and transmits the drive from the output shaft  23  to the auxiliary transmission  40 . Details of the main transmission  20  are as follows. 
     The HST case  21  includes a main HST case body  21 C formed of cast iron and a port block  21 P also formed of cast iron. The main HST case body  21 C has a flange  21   a  bolted to the transmission case part  10   b  of the main clutch housing  10 , and a recess  21   b  opening rearwardly of the vehicle body. The port block  21 P is bolted to a rear end surface of the main HST case body  21 C to close the opening of recess  21   b , and defines a flange bolted to the main transmission case body  5   a . The HST case  21  has an oil chamber  24  defined by the recess  21   b  for accommodating the hydraulic pump P and hydraulic motor M along with oil. Thus, the hydraulic pump P and hydraulic motor M are arranged in an oil sump to be free from air. 
     The hydraulic pump P and hydraulic motor M are arranged in the oil chamber  24  transversely of the vehicle body. The hydraulic pump P is in the form of an axial plunger pump. The hydraulic pump P includes a plurality of plungers  25  arranged around the input shaft  22  of the main transmission  20 , a cylinder block  26  slidably receiving these plungers  25  and rotatable about the axis of input shaft  22 , and a ring-shaped swash plate  27  fitted adjacent one end of input shaft  22  and pivotable relative to the HST case  21 . The hydraulic motor M is in the form of an axial plunger motor. The hydraulic motor M includes a plurality of plungers  28  arranged around the output shaft  23  of the main transmission  20 , a cylinder block  29  slidably receiving these plungers  28  and rotatable with the output shaft  23 , and a swash plate  30  mounted in HST case  21  and formed integral with the main HST case body  21 C. With rotation of the cylinder block  29 , the swash plate  30  causes the plungers  28  to slide back and forth relative to the cylinder block  29 . The swash plate  30  has a cam plate attached thereto and defining a cam surface  30   a . The cam surface  30   a  is inclined to extend laterally outwardly and rearwardly of the vehicle body. 
     As shown in FIGS. 5 and 7, the hydraulic pump P has two arc-shaped inlet/outlet ports  31   a  and  31   b  juxtaposed transversely of the vehicle body. The inlet/outlet ports  31   a  and  31   b  are formed in an inward portion of port block  21 P and a valve plate  32  fixed to an inward surface of port block  21 P. The hydraulic motor M also has arc-shaped inlet/outlet ports  33   a  and  33   b  formed in the inward portion of port block  21 P and a valve plate  34  fixed to the inward surface of port block  21 P. The inlet/outlet ports  33   a  and  33   b  of motor M are arranged vertically of the vehicle body. That is, the inlet/outlet ports  33   a  and  33   b  of motor M are arranged in a different direction to the inlet/outlet ports  31   a  and  31   b  of pump P. One inlet/outlet port  31   a  of the pump and one inlet/outlet port  33   a  of the motor are connected to each other by an oil line  35   a  in the form of a bore in the port block  21 P. The other inlet/outlet port  31   b  of the pump and the other inlet/outlet port  33   b  of the motor are connected to each other by an oil line  35   b  in the form of another bore in the port block  21 P. That is, when ouputting forward drive, the inlet/outlet port  31   a  or  31   b  of hydraulic pump P acts as a drain port, and the inlet/outlet port  33   a  or  33   b  of hydraulic motor M communicating therewith acts as an intake port. At this time, the other inlet/outlet port  33   b  or  33   a  of hydraulic motor M acts a drain port, and the inlet/outlet port  31   b  or  31   a  of hydraulic pump P communicating therewith acts as an intake port. Conversely, when outputting backward drive, the other inlet/outlet port  31   b  or  31   a  of hydraulic pump P acts as a drain port, and the inlet/outlet port  33   b  or  33   a  of hydraulic motor M communicating therewith acts as an intake port. At this time, the other inlet/outlet port  33   a  or  33   b  of hydraulic motor M acts as a drain port, and the inlet/outlet port  31   a  or  31   b  of hydraulic pump P communicating therewith acts as an intake port. In either case, i.e. whether to output forward drive or backward drive, pressure oil is supplied from the hydraulic pump P to the hydraulic motor M through the oil line  35   a  or  35   b , and returned from the hydraulic motor M to the hydraulic pump P through the oil line  35   b  or  35   a.    
     As shown in FIG. 5, the swash plate  27  of hydraulic pump P has an angle variable by a swash plate control unit  60  including a hydraulic servo cylinder  61  and a hydraulic servo valve  62  as main components thereof. The servo cylinder  61  is incorporated into a cylinder mount  21   d  formed integral with the main HST case body  21 C to be on the left side surface (the side surface adjacent the hydraulic pump P) of HST case  21 . The longitudinal direction of servo cylinder  61  extends vertically of the vehicle body. The servo cylinder  61  has a control pin  61   a  projecting therefrom into engagement with the swash plate  27 . The hydraulic servo valve  62  is attached to an outer surface of cylinder mount  21   d , with the longitudinal direction of valve  62  extending vertically of the vehicle body. 
     FIGS. 8 and 9 show details of the servo valve  62  and a valve controller  66 . The servo valve  62  has a control lever  63  supported by a valve case  65  through a rotary support shaft  64 . The valve controller  66  extends from the rotary support shaft  64 . The valve controller  66  is engaged with one end of a valve control link  67  through a coupling pin  66   a . The other end of valve control link  67  is engaged with the servo cylinder  61 . The valve control link  67  is connected in an intermediate position thereof to a valve spool  68  by a coupling pin  67   a . In this construction, when the control lever  63  is swung about the axis of rotary support shaft  64 , the rotary support shaft  64  rotates with the control lever  63 . The valve controller  66  pivots in the valve case  65  about the axis of rotary support shaft  64 , which swings the valve control link  67  through the coupling pin  66   a  (the valve control link  67  being pivotable about the other end engaged with the servo cylinder  41 ). Then, the coupling pin  67   a  of valve control link  67  moves from a neutral position in the same direction as the direction of movement of coupling pin  66   a , to switch the valve spool  68  from the neutral position to a drive position. When the valve spool  68  is switched to the drive position, the servo cylinder  61  is driven by pressure oil. As shown in FIG. 5, the control pin  61   a  swings the swash plate  27  to a forward drive position or a backward drive position and in an accelerating or decelerating direction corresponding to the direction of movement of the control lever  63 . The servo cylinder  61  swings the swash plate  27  while swinging the valve control link  67 . (At this time, the valve control link  67  pivots about the coupling pin  66   a  of valve controller  66 ). When the swing of the swash plate  27  reaches an angle proportional to the stroke of control lever  63 , the coupling pin  67   a  of valve control link  67  returns to the neutral position to return the valve spool  68  to the neutral position. Thus, when the swash plate  27  moves in a direction corresponding to the direction of movement of control lever  63  and by an angle proportional to the stroke of control lever  63 , the servo valve  62  automatically returns to neutral. The servo cylinder  61  stops to stop the swash plate  27 . 
     As shown in FIGS. 5 through 7 and  11 , the stepless transmission  20  has three bores  36 - 38 . Each bore is defined by a pipe extending from a front wall of the main HST case body  21 C to the port block  21 P. The first bore  36  located at the highest level receives the input shaft  51  of the implement driving transmission  50 . The second bore  37  at an intermediate level is provided for circulating a lubricant through interiors of transmission case part  10   b  and transmission case  5 . The third bore  38  at the lowest level receives the front wheel transmission shaft  19 . 
     FIG. 10 shows a speed control structure for controlling the stepless transmission  20 . This speed control structure includes a change speed pedal  71  supported by a driving deck  70 . As shown in FIG. 15, the change speed pedal  71  is a single pedal integrating a forward drive control end  71   a  and a backward drive control end  71   b . The forward drive control end  71   a  is offset laterally outwardly from the backward drive control end  71   b . Thus, the forward drive control end  71   a  may be depressed with ease by the tip of a foot, and the backward drive control end  71   b  by the heel. In FIG. 10, numeral  71   c  denotes an output to an interlocking mechanism  73  (described hereinafter), and numeral  71   d  denotes a fulcrum or pivotal axis of the change speed pedal  71 . The pivotal axis  71   d  extends through a bracket  72  supported on the driving deck  70 . 
     The change speed pedal  71  is located at a higher level than the stepless transmission  20 . As seen from a side of the vehicle body, the rear end of the forward drive control end  71   a  of change speed pedal  71  lies over the stepless transmission  20  in the fore and aft direction of the vehicle body. The stepless transmission  20  is located forwardly of the pivotal axis  71   d  of change speed pedal  71 . 
     The interlocking mechanism  73  operatively connecting the change speed pedal  71  to the servo valve  62  provided for the swash plate control unit  60  of the hydraulic pump P includes a link  74 , a first rod  75  and a second rod  76 . The link  74  is supported, to be pivotable about a transverse axis P 1 , by a support member  77  bolted to a side of body frame F. Thus, the link  74  is supported by the body frame F to be pivotable about the axis P 1 . The link  74  has four, first to fourth connection points  74   a - 74   d  distributed around the axis P 1 , and one cam follower  74   e . The first rod  75  interlocks the link  74  to the change speed pedal  71  by connecting the first connection point  74   a  located forwardly of the axis P 1  to the output  71   c  of change speed pedal  71 . The first rod  75 , when mounted in place, extends vertically of the vehicle body, and substantially perpendicular to the driving deck  70  through a bore  70 A formed therein. The second rod  76  interlocks the link  74  to the control lever  63  of servo valve  62  by connecting the second connection point  74   b  located below the pivotal axis P 1  and first connection point  74   a  to the control lever  63 . The second rod  76 , when mounted in place, extends substantially along the fore and aft direction of the vehicle body. 
     A cam member  78  is provided to impart an operational resistance to the change speed pedal  71  and control lever  63  and apply a force for automatically returning these components to their neutral positions. For this purpose, the cam member  78  has a cam  78   a  in the form of a roller attached to an intermediate position thereof. The cam  78   a  acts on the cam follower  74   e  located rearwardly of the pivotal axis P 1  of link  74 . The cam member  78  is supported by the support member  77  to be pivotable about a transverse axis P 2 . Thus, when the support member  77  is assembled to the body frame F, the cam member  78  and link  74  are assembled to the body frame F all at once. A spring  79  extends between the cam member  78  and support member  77 . The spring  79  biases the cam member  78  toward the link  74  to place the cam  78   a  in contact with the cam follower  74   e  of link  74 . The cam  78   a  of cam member  78  is pressed by the elastic restoring force of spring  79  against a curved portion of cam follower  74   e , thereby to apply a resistance to the pivotal movement of the link  74 . The position of the link  74  at this time places the change speed pedal  71  and control lever  63  in the neutral positions. 
     Numeral  80  denotes a damper. Numeral  81  denotes a damper holder for supporting a rod  80   a  of damper  80 . Numeral  82  denotes a support member fixed to the body frame F for pivotably supporting the damper holder  81 . The damper  80  has a tube  80   b  disposed opposite the first rod  75  and second rod  76  across the link  74 . The tube  80   b  is pivotally connected to the fourth connection point  74   d  located above the pivotal axis P 1 . The damper  80  in this way damps any vibration of the change speed pedal  71  and control lever  63  through the link  74 , which vibration may be transmitted from the swash plate  27 . Further, the damper  80  imparts an operational resistance to the change speed pedal  71  through the link  74  and the first rod  75  to prevent a sudden operation of the change speed pedal  71 . 
     The link  74  includes three components, i.e. a first arm  74 A, a second arm  74 B and the cam follower  74   e . The first arm  74 A has a boss  74   f  connected to the support member  77 , and the second connection point  74   b , third connection point  74   c  and fourth connection point  74   d . The second arm  74 B is connected to the boss  74   f  to be pivotable therewith, and has the first connection point  74   a . The cam follower  74   e  is connected to the boss  74   f  to be pivotable therewith. 
     When the driver depresses the forward drive control end  71   a  from the neutral position of change speed pedal  71 , this control force is transmitted to the control lever  63  of servo valve  62  through the interlocking mechanism  73 . Consequently, the control lever  63  pivots forwardly of the vehicle body to switch the servo valve  62  to a forward position, which switches the stepless transmission  20  from neutral to the forward drive position. As a result, the vehicle body runs forward. When the driver further depresses the forward drive control end  71   a , the control lever  63  pivots to an increased extent forwardly of the vehicle body, thereby enlarging a swash plate angle variable by the servo cylinder  61 , whereby the stepless transmission  20  provides a higher speed. As a result, the vehicle is accelerated in running forward. On the other hand, when the driver depresses the backward drive control end  71   b  from the neutral position of change speed pedal  71 , this control force is transmitted to the control lever  63  of servo valve  62  through the interlocking mechanism  73 . Consequently, the control lever  63  pivots rearwardly of the vehicle body to switch the servo valve  62  to a backward position, which switches the stepless transmission  20  from neutral to the backward drive position. As a result, the vehicle body runs backward. When the driver further depresses the backward drive control end  71   b , the control lever  63  pivots to an increased extent rearwardly of the vehicle body, thereby enlarging a swash plate angle variable by the servo cylinder  61 , whereby the stepless transmission  20  provides a higher speed. As a result, the vehicle is accelerated in running backward. 
     When the driver releases the change speed pedal  71  during a forward or backward run, the change speed pedal  71  and control lever  63  are automatically returned to the neutral positions by the neutral restoring action of the cam member  78  as already described. Consequently, the stepless transmission  20  is switched to the decelerating position to decelerate the vehicle. Finally, the change speed pedal  71  and control lever  63  are restored to the neutral positions to return the stepless transmission  20  to neutral, thereby stopping the vehicle. At this time, the control lever  63  and change speed pedal  71  are firmly retained in the neutral positions by the damping action of the damper  80  and the positioning action of the cam member  78 . 
     As shown in FIG. 11, the driving deck  70  includes a main deck body  70   a  formed of sheet metal and supported by the body frame F, and a rubber sheet cushion  70   b  laid on the upper surface of main deck body  70   a . The main deck body  70   a  is attached to the body frame F in a plurality of fore and aft positions at each side by mounting structures as shown in FIG.  11 . Specifically, each mounting element  70   c  on the lower surface of the main deck body  70   a  is placed on a deck support member  83  through a rubber cushion  84  and retained in place by a mounting bolt  85  extending through the rubber cushion  84 . Thus, the driving deck  70  is supported by the body frame F through the rubber cushions  84  to damp vibration from the body frame F. The deck support member  83  is connected, for example, to a side of the main transmission case body  5   a  forming the body frame F. 
     As shown in FIG. 10, a speed retainer  87  is connected through a rod  86  to the third connection point  74   c  which is located below and rearwardly of the pivotal axis P 1  of the link  74 . This speed retainer  87  is disposed opposite the first rod  75  and second rod  76  across the link  74 . As shown in FIG. 12, the speed retainer  87  is pivotably supported by an upper portion of the main transmission case body  5   a  through a rotary support shaft  88 . 
     As shown in FIGS. 12 and 13, a lock  89  is disposed on the side surface of the main transmission case body  5   a  opposite from the speed retainer  87  for locking and unlocking the speed retainer  87 . This lock  89  forms part of a cruising device for locking the stepless transmission  20  to a desired running speed. 
     Specifically, the speed retainer  87  is connected to one end of the rotary support shaft  88 , and a lock arm  90  is connected to the other end thereof (at the same side of the main transmission case body  5   a  where the lock  89  is disposed), to be pivotable with rotation of the rotary support shaft  88 . The lock  89  has sawteeth  89   a  for acting on the lock arm  90  by engaging an engaging piece  90   a  disposed at a distal end of the lock arm  90 . The lock  89  is supported by a support member  91  bolted to a side of the main transmission case body  5   a , to be pivotable about an axis P 3 , and is biased to an unlock position by an unlock spring  93 . In the unlock position, the unlock spring  93  contacts a stopper pin  92  behind the sawteeth  89   a . The lock  89  is pivotable by a control member  95  slidably attached to a panel B disposed below the steering wheel  3 . The control member  95  is operatively connected to a free end  89   b  of the lock  89  through a pivotal link  95   a  and a control cable  94 . 
     In the above construction, the driver draws the control member  95  from the panel B toward the driver&#39;s seat  4  while depressing the change speed pedal  71  to the forward side to set the stepless transmission  20  to a desired speed. The lock  89  thereby pivots about the axis P 3  clockwise in FIG. 13 against the biasing force of the unlock spring  93  to engage the sawteeth  89   a  with the engaging piece  90   a  of the lock arm  90 . The engagement of lock  89  and lock arm  90  is maintained against the biasing force of unlock spring  93 . The lock  89  locks the speed retainer  87  through the lock arm  90  and rotary support shaft  88  to a position corresponding to the set speed of the stepless transmission  20  against the neutral restoring force of the cam member  78 . As shown in FIG. 10, the speed retainer  87  locked in this way locks the control lever  63  of pump control unit  60  through the rod  86 , link  74  and second rod  76  and against the neutral restoring force, to a position set by the change speed pedal  71 . Thus, the stepless transmission  20  may be fixed to the desired speed set by the change speed pedal  71 , When, in this state, the driver pushes the control member  95  back to the panel B to cancel the engagement between the lock  89  and lock arm  90 , the lock  89  returns to the unlock position under the biasing force of the unlock spring  93 , thereby releasing the speed retainer  87  to unlock the stepless transmission  20  from the set speed. 
     As shown in FIG. 13, the other free end (remote from the free end  89   b  to which the control cable  94  is connected) of the lock  89  has, connected thereto, one end of a control cable  96  interlocked to a pair of right and left brake pedals  97   a  and  97   b . An interlock regulating mechanism  100  is disposed between the other end of control cable  96  and the pair of right and left brake pedals  97   a  and  97   b  for regulating the interlocking between the lock  89  and the two brake pedals  97   a  and  97   b.    
     As shown in FIGS. 13 and 14, the interlock regulating mechanism  100  includes a left control arm  101   a  extending from a boss of left brake pedal  97   a  to be pivotable therewith, a right control arm  101   b  longer than the left control arm  101   a  and extending from a boss of right brake pedal  97   b  to be pivotable therewith, a lock control link  102  disposed between the right and left control arms  101   a  and  101   b  and connected to the control cable  96 , a left control link  103   a  having one end thereof pivotally connected to the lock control link  102  and the other end pivotally connected to a free end of the left control arm  101   a , and a right control link  103   b  having one end thereof pivotally connected to the lock control link  102  and the other end pivotally connected to a free end of the right control arm  101   b.    
     FIGS.  16 ( a ), ( b ) and ( c ) illustrate operation of the interlock regulating mechanism  100 . When only the left brake pedal  97   a  is depressed as shown in FIG.  16 ( a ), the left control arm  101   a  pivots with the pedal  97   a  but the right control arm  101   b  remains still. The left control link  103   a  only pivots about a point of connection  104  with the lock control link  102  and does not move the lock control link  102 . As a result, the lock control link  102  does not pull the control cable  96 . When only the right brake pedal  97   b  is depressed as shown in FIG.  16 ( b ), the right control arm  101   b  pivots with the pedal  97   b  but the left control arm  101   a  remains still. The right control link  103   b  only pivots about the point of connection  104  with the lock control link  102  and does not move the lock control link  102 . As a result, the lock control link  102  does not pull the control cable  96 . When both the left brake pedal  97   a  and right brake pedal  97   b  are depressed as shown in FIG.  16 ( c ), the left control arm  101   a  and right control arm  101   b  pivot to move the lock control link  102  in the direction of movement of the control arms  101   a  and  101   b  through the left control link  103   a  and right control link  103   b . As a result, the lock control link  102  pulls the control cable  96  to switch the lock  89 , if in the lock position, from the lock position to the unlock position. 
     That is, even when the driver brakes only one of the right and left rear wheels  2  during a run with the stepless transmission  20  locked to a set speed, the stepless transmission  20  is not released from the set speed. The vehicle can make a small turn with an outer one of the rear wheels driven at the set speed. When the driver brakes both of the right and left rear wheels  2 , the stepless transmission  20  is automatically released from the set speed to be switchable to a non-drive state. 
     The body frame F may be constructed as shown in FIG.  22 . In this modification, the HST case  21  of the stepless transmission  20  is formed simultaneously with the main clutch housing  10 . Thus, the HST case  21  is formed integral with the main clutch housing  10 . 
     [Other Embodiment] 
     FIGS. 17 through 21 show another embodiment of this invention. In this embodiment, the change speed pedal  71  pivotably supported on the driving deck  70  and the control lever  63  of stepless transmission  20  are connected to each other through an interlocking mechanism  110  which takes the place of the interlocking mechanism  73  of the preceding embodiment. Further, the stepless transmission  20  may be locked to a set speed by a cruising device different from what is used in the preceding embodiment. 
     As shown in FIG. 17, the interlocking mechanism  110  includes an interlocking rod  111  having one end thereof connected to the change speed pedal  71 , a first pivotal link  112  connected to the other end of the interlocking rod  111  and supported by the body frame F to be pivotable about an axis P 4 , a push-pull link  113  having one end thereof connected to the first pivotal link  112 , a second pivotal link  114  connected to the other end of the push-pull link  113  and supported by the body frame F to be pivotable about an axis P 5 , and an interlocking rod  115  connecting the second pivotal link  114  to the control lever  63  of servo valve  62  provided for the control unit  60  of stepless transmission  20 . 
     A support member  116  is bolted to a side of body frame F. The first pivotal link  112  and second pivotal link  114  are connected to the support member  116  to be pivotable about the axes P 4  and P 5 , thereby being pivotably supported by the body frame F. The second pivotal link  114  includes a link element  114   a  having a boss  114   b  connected to the support member  116  and a point of connection to the push-pull link  113 , and a cam plate  114   c  connected to the boss  114   b  to be pivotable therewith and having a point of connection to the interlocking rod  115 . A damper  80  similar to the damper  80  shown in FIG. 10 is connected between the link element  114   a  of second pivotal link  114  and the support member  116 . The cam plate  114   c  of second pivotal link  114  has a cam follower  114   c  similar to the cam follower  74   e  shown in FIG. 10. A cam member  117  has a cam  117   a  in the form of a roller disposed in an intermediate position thereof for contacting the cam follower  114   c . The cam member  117  has one end thereof pivotably supported by the support member  116 , and the other end connected to the support member  116  through a spring  118 . The spring  118  biases the cam member  117  toward the second pivotal link  114 , whereby the cam  117   a  of second pivotal link  114  contacts the cam follower  114   c . The cam member  117 , with the cam  117   a  pressing against the cam follower  114   c  of second pivotal link  114 , applies an operational resistance and a neutral restoring force to the change speed pedal  71  and control lever  63 . 
     With the above construction, when the driver depresses the forward drive control end  71   a  of change speed pedal  71 , this control force causes the control lever  63  of servo valve  62  to pivot forwardly. This switches the stepless transmission  20  from neutral to the forward drive position. When the driver further depresses the forward drive control end  71   a , the stepless transmission  20  provides a higher forward speed. When the driver depresses the backward drive control end  71   b  of change speed pedal  71 , this control force causes the control lever  63  to pivot rearwardly. This switches the stepless transmission  20  from neutral to the backward drive position. When the driver further depresses the backward drive control end  71   b , the stepless transmission  20  provides a higher backward speed. 
     In the example shown in FIGS. 17 through 20, the second pivotal link  114  and a speed retainer  130  are interlocked through a cruise regulating mechanism  120 . The speed retainer  130  is supported to be pivotable through a rotary support shaft  131  by an upper portion of the main transmission case body  5   a.    
     An interlocking mechanism  132  is disposed at an end of the rotary support shaft  131  remote from the speed retainer  130 . The interlocking mechanism  132  includes a pivotal link  132   a  connected to the end of the rotary support shaft  131  to be pivotable therewith, a plurality of other pivotal links, and interlocking rods interconnecting the pivotal links. A swing arm  133  is coupled to the above end through this interlocking mechanism  132 . The swing arm  133  is pivotably supported by a vertical support shaft  135  extending through a bracket  134  supported by a steering column in the driving section. A cruise lever  136  is supported by the bracket  134  through the support shaft  135 , to be pivotable about the same axis and relative to the swing arm  133 . The cruise lever  136  has a stopper arm  136   a  extending from a proximal end to be pivotable therewith and to act on the swing arm  133 . On opposite, upper and lower sides of a proximal portion of cruise lever  136  are friction elements  137  slidably fitted on the support shaft  135 . A spring case  138  also is slidably fitted on the support shaft  135 . This spring case  138  contains a lever retaining spring  139  which, combined with the friction elements  137 , forms a cruise lever retaining mechanism  140  for retaining the cruise lever  136  in a selected position from neutral position N to a maximum forward speed position Fmax. That is, the lever retaining spring  139  acts to press the cruise lever  136  against a lever support  134   a  of the bracket  134  through the spring case  138  and friction elements  137 . A frictional force produced at this time retains the cruise lever  136  in a selected position against the neutral restoring force of the cam member  117 . 
     As shown in FIG. 17, the cruise regulating mechanism  120  includes an interlocking rod  121  having one end thereof pivotally connected to the second pivotal link  114  and the other end defining a slot  121   a , a connecting pin  122  connected to the speed retainer  130  and having a distal end thereof slidably fitted in the slot  121   a , a hook  124  pivotably supported by the interlocking rod  121  adjacent the slot  121   a  to couple the connecting pin  122  and interlocking rod  121 , a hook spring  123  for biasing the hook  124  to a position for engaging the connecting pin  122 , and a hook actuator  125  supported by a support member  116  to act on a proximal end of hook  124 . 
     FIGS.  21 ( a ) and ( b ) show operations of the cruise regulating mechanism  120 . When the control lever  63  is in the forward drive position, as shown in FIG.  21 ( a ), the interlocking rod  121  moves toward the speed retainer  130  relative to the hook actuator  125 , whereby the hook actuator  125  departs from the proximal end of hook  124  to stop pressing the same. As a result, the hook  124 , under the biasing force of hook spring  123 , engages the connecting pin  122  to couple the connecting pin  122  to the interlocking rod  121 . With the connection between the connecting pin  122  and interlocking rod  121 , the interlocking rod  121  is linked with the speed retainer  130 . As a result, a linkage is established from the swing arm  133  to the control lever  63 . The action of the stopper arm  136   a  of cruise lever  136  to stop the swing arm  133  reaches the control lever  63 . 
     On the other hand, when the control lever  63  in the backward drive position, as shown in FIG.  21 ( b ), the interlocking rod  121  moves away from the speed retainer  130  relative to the hook actuator  125 , whereby the hook actuator  125  presses the proximal end of hook  124 . As a result, the hook  124  is disengaged from the connected pin  122  against the biasing force of hook spring  123  to uncouple the connecting pin  122  from the interlocking rod  121 . Consequently, the above linkage between the interlocking rod  121  and speed retainer  130  is canceled, and so is the linkage between the swing arm  133  and control lever  63 . The action of the stopper arm  136   a  of cruise lever  136  to stop the swing arm  133  does not reach the control lever  63 . 
     In this cruising device, as shown in FIG. 19, the cruise lever  136  is pivotable about the axis of support shaft  135  along a guide groove  141   a  of a lever guide  141  to set a forward speed. The stepless transmission  20  is locked to the set forward speed. The cruising device locks the stepless transmission  20  only to a selected forward speed. As for backward drive, the cruise regulating mechanism  120  allows the stepless transmission  20  to be controlled freely by the change speed pedal  71  while the cruise lever  136  is set to neutral position N. An operation of the cruise regulating mechanism  120  for suppressing the cruising action for backward drive will be described hereinafter. 
     When the driver rocks the cruise lever  136  from neutral position N to maximum forward speed position Fmax against the frictional force of the cruise lever retaining mechanism  140 , the stopper arm  136   a  of cruise lever  136  contacts the swing arm  133  and swings the swing arm  133  about the axis of support shaft  135 . Consequently, the swing arm  133 , through the interlocking mechanism  132  and rotary support shaft  131 , causes the speed retainer  130  at the other end of support shaft  131  to pivot upward. Then, the speed retainer  130 , through the cruise regulating mechanism  120 , second pivotal link  114  and interlocking rod  115 , causes the control lever  63  of servo valve  62  to pivot to the forward drive position. The driver stops the cruise lever  136  at a desired position. Then, the cruise lever  136  is retained in that position by the cruise lever retaining mechanism  140 . The stopper arm  136   a  acts to stop the swing arm  133 . The swing arm  133 , through the link mechanism  132  and rotary support shaft  131 , holds the speed retainer  130  in a position corresponding to the position of the cruise lever  136 , against the neutral restoring force of cam member  117 . As a result, the speed retainer  130 , through the cruise regulating mechanism  120 , second pivotal link  114  and interlocking rod  115 , retains the control lever  63  in a forward speed position corresponding to the position of the cruise lever  136  against the neutral restoring force of cam member  117 . During a forward run, the swing arm  133  is swung away from the stopper arm  136  by depressing the forward drive control end  71   a  of change speed pedal  71 , whereby the control lever  63  pivots to a higher speed position. Thus, the driver can control the stepless transmission  20  for a higher speed than the speed set by the cruise lever  136 . When, in this state, the driver releases the change speed pedal  71 , the stepless transmission  20 , under the restoring force of cam member  117 , automatically decelerates to the forward speed set by the cruise lever  136 . 
     During a backward run, on the other hand, the driver depresses the backward drive control end  71   b  of change speed pedal  71  after setting the cruise lever  136  to neutral position N. Then, the cruise regulating mechanism  120  cancels the connection between the second interlocking link  114  and speed retainer  130 . Consequently, the stopping action of the stopper arm  136   a  of cruise lever  136  does not reach the second pivotal link  114 . Although the cruise lever  136  is set to neutral position N, the driver can swing the control lever  63  to the backward position to control the stepless transmission  20  for varying backward speeds. 
     As shown in FIG. 20, a cruise release device  142  is attached to the spring case  138 . This cruise release device  142  is connected to the right and left brake pedals  79   a  and  79   b  through a control cable  143  and an interlock regulating mechanism  100  similar to that shown in FIG.  13 . With this construction, when the driver depresses both the right and left brake pedals  79   a  and  79   b , the control cable  143  is pulled by the interlocking mechanism  100 . Under the tension of the cable  143 , the cruise release device  142  pulls the spring case  138  away from the lever support  134   a  of bracket  134 . As a result, the lever retaining spring  139  is compressed toward a spring bearing  144  to release the cruise lever  136  from the frictional retention by the cruise lever retaining mechanism  140 . That is, by braking both the right and left rear wheels  2 , the stepless transmission  20  is freed from a speed set by the cruise lever  136 , thereby allowing the vehicle to stop. When only one of the right and left brake pedals  79   a  and  79   b  is depressed, the control cable  143  is not pulled by the interlocking mechanism  100 . Thus, the cruise release device  142  does not compress the lever retaining spring  139 . The cruise lever retaining mechanism  140  frictionally retains the cruise lever  136  in a selected position. Thus, when the driver brakes only one of the right and left rear wheels  2 , the stepless transmission  20  remains locked to a speed set by the cruise lever  136 . The vehicle can make a small turn while driving an outer one of the rear wheels at a fixed speed.