Patent Abstract:
A work vehicle with a speed change device, comprises, a plurality of wheels including at least one driven wheel; an engine for driving the driven wheel; a speed change device provided between the driven wheel and the engine; and automatic shifting mechanism. The automatic shifting mechanism is capable of operating the speed change device to a lower speed position within an automatic shifting range having a predetermined range and is capable of operating the speed change device up to a speed position which the speed change device was in before an operation to the lower speed position was effected, in response to load on the engine. The entirety of the automatic shifting range is changeable to a low speed side and to a high speed side, or the automatic shifting range can be widened to include more speed positions and narrowed to include less speed positions.

Full Description:
BACKGROUND OF THE INVENTION 
   As disclosed by the Japanese Publication No. 2002-106697 (FIGS. 1, 2, 4 and 6), for example, a conventional work vehicle is constructed to operate a propelling speed change device automatically to a low speed side and a high speed side in response to loads acting on the engine. 
   This work vehicle detects an actual engine speed for determining a load acting on the engine. When the actual engine speed lowers, the propelling speed change device is operated to the low speed side. When the actual engine speed rises, the propelling speed change device is operated to the high speed side. By operating the propelling speed change device to the low speed side and high speed side, the actual engine speed is maintained in a set range (i.e. the load acting on the engine is maintained in a set range). 
   Generally, with a work vehicle, it is necessary to set a proper running speed according to the type of implement connected to the vehicle, and conditions of the operating ground. 
   SUMMARY OF THE INVENTION 
   The object of this invention is provide a work vehicle constructed to operate a propelling speed change device to a low speed side and a high speed side according to loads acting on an engine, the vehicle being capable of setting a proper running speed according to working conditions. 
   The above object is fulfilled, according to one aspect of the invention, by a work vehicle with a speed change device, comprising: a plurality of wheels including at least one driven wheel; an engine for driving said at least one driven wheel; a speed change device provided between said at least one driven wheel and said engine; and an automatic shifting means for operating said speed change device to a lower speed position within an automatic shifting range having a predetermined range and for operating said speed change device up to a speed position said speed change device was in before an operation to the lower speed position was effected, in response to load on said engine, wherein an entirety of said automatic shifting range is changeable to a low speed side and to a high speed side. 
   Thus, the automatic shifting device is capable of operating the speed change device to a lower speed position within an automatic shifting range having a predetermined range and is capable of operating the speed change device up to a speed position which the speed change device was in before an operation to the lower speed position was effected. Thus, the propelling speed change device is not automatically operated to the low speed side and high speed side beyond the automatic shifting range. And the entire automatic shifting range is changeable to the low speed side and high speed side. Thus, the automatic shifting range may be set appropriately according to working conditions. 
   The speed change performance of work vehicles can also be improved by providing a mechanism that can widen the automatic shifting range to include more speed positions and narrow the range to include less speed positions. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view showing a transmission system in a transmission case; 
       FIG. 2  is a view showing a linkage among a shift lever, an up-shift button and a down-shift button, a setting switch and various other components; 
       FIG. 3  is a hydraulic circuit diagram showing forward and backward clutches, first and second main speed change devices, and so on; 
       FIG. 4  is a view showing a flow of control in time of operating a forward and backward drive switching lever; 
       FIG. 5  is a view showing a flow of control in time of pushing the up-shift button and down-shift button in a manual mode; 
       FIG. 6  is a view showing states of a first to a fourth speed clutches and a low speed and a high speed clutches in time of pushing the up-shift button and down-shift button in the manual mode; 
       FIG. 7  is a view showing a flow of control for operating the first and second main speed change devices automatically to a low speed side and a high speed side in a load mode; 
       FIG. 8  is a view showing the first half of a flow of control for operating the first and second main speed change devices automatically to the low speed side and the high speed side in a run mode; 
       FIG. 9  is a view showing the second half of the flow of control for operating the first and second main speed change devices automatically to the low speed side and the high speed side in the run mode; 
       FIG. 10  is a view showing a flow of control for setting an automatic speed change range in the load mode (run mode); 
       FIG. 11  is a view showing the first half of a flow of control for changing the automatic speed change range in the load mode (run mode); 
       FIG. 12  is a view showing the second half of the flow of control for changing the automatic speed change range in the load mode (run mode); 
       FIG. 13  is a view showing a relationship between position of a sensitivity adjusting switch, and first and second set values; 
       FIG. 14  a view showing a flow of control for setting an automatic speed change range in the load mode (run mode) in a different embodiment; 
       FIG. 15  is a view showing states of a speed indicator in another different embodiment; and 
       FIG. 16  is a view showing states of a speed indicator in a further embodiment. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Next, some embodiments of this invention will be described with reference to the drawings. It should be understood that a combination of a characteristic feature described in a certain embodiment with a characteristic feature described in a different embodiment is, unless a conflict occurs, within the scope of this invention. 
   [1] 
     FIG. 1  shows a transmission case  8  of the four-wheel drive type agricultural tractor which is one example of work vehicles. Power of an engine  1  is transmitted to a pair of rear wheels  14  through a forward clutch  5  or a backward clutch  6 , a tubular shaft  7 , a first main speed change device  10  (corresponding to the propelling speed change device), a second main speed change device  11 , an auxiliary speed change device  12  and a rear wheel differential  13 . The power branched off immediately upstream of the rear wheel differential  13  is transmitted to a pair of front wheels  19  through a transmission shaft  15 , a front wheel speed change device  16  of the hydraulic clutch type, a front wheel transmission shaft  17  and a front wheel differential  18 . The power of the engine  1  is transmitted also to a PTO shaft  4  through a transmission shaft  2 , a PTO clutch  3  and a PTO speed change device  9  of the hydraulic multi-plate type. 
   As shown in  FIG. 1 , each of the forward and backward clutches  5  and  6  is the hydraulic multi-plate type having a combination of friction plates (not shown) and a piston (not shown), and is engageable by supplying hydraulic fluid. When the forward clutch  5  is engaged, the power of the engine  1  is transmitted from the forward clutch  5  directly to the tubular shaft  7  to drive the vehicle body forward. When the backward clutch  6  is engaged, the power of the engine  1  is transmitted through the backward clutch  6  and a transmission shaft  20  to the tubular shaft  7  in reversed rotation, to drive the vehicle body backward. 
   As shown in  FIG. 1 , the first main speed change device  10  is the hydraulic clutch type having a first speed clutch  21 , a second speed clutch  22 , a third speed clutch  23  and a fourth speed clutch  24  arranged in parallel, to provide four speeds. By selectively engaging the first to fourth speed clutches  21 - 24 , the power on the tubular shaft  7  is transmitted to a transmission shaft  25  in four speeds. 
   As shown in  FIG. 1 , the second main speed change device  11  is the hydraulic clutch type having a low-speed clutch  26  and a high-speed clutch  27  arranged in parallel. By selectively engaging the low-speed and high-speed clutches  26  and  27 , the power on the transmission shaft  25  is transmitted in two speeds to the auxiliary speed change device  12 . The auxiliary speed change device  12  is the synchromesh type with a slidable shift element  53  for providing two speeds, and is mechanically operable by a shift lever  28  shown in  FIG. 2 . 
   A control unit shown in  FIG. 2  has a CPU and memory, receives signals from switches and sensors to be described in this specification, generates control signals for controlling actuators of valves, and transmits the control signals to required components. Thus, even if not expressly described in the specification, each switch, each sensor, and each actuator and the control unit are in signal communication. The memory of the control unit stores one or more programs for executing a control algorism described in this specification. 
   [2] 
   A hydraulic circuit for the forward and backward clutches  5  and  6  and first and second main speed change devices  10  and  11  will be described next. 
   As shown in  FIG. 3 , an oil line  30  extending from a pump  29  has, connected thereto, an electromagnetic proportional valve  35  and selector valves  36   a  and  37   a  of the pilot operated type for the forward and backward clutches  5  and  6 , selector valves  31   a,    32   a,    33   a  and  34   a  of the pilot operated type for the first to fourth speed clutches  21 - 24 , and electromagnetic proportional valves  38  and  39  for the low-speed and high-speed clutches  26  and  27 . 
   As shown in  FIG. 3 , an oil line  40  branched from the oil line  30  has, connected thereto, a selector valve  42   a  of the pilot operated type for a hydraulic clutch  41  for differential locking of the front wheel differential  18 , a selector valve  44   a  of the pilot operated type for a hydraulic clutch  43  for differential locking of the rear wheel differential  13 , and selector valves  47   a  and  48   a  of the pilot operated type for a standard clutch  45  and an accelerating clutch  46  of the front wheel speed change device  16 . The selector valves  31   a - 34   a,    36   a,    37   a,    42   a,    44   a,    47   a  and  48   a  are biased by springs to drain positions (disengaging positions), and are operated to supply positions (engaging positions) by pilot pressure supplied. 
   As shown in  FIG. 3 , a pilot oil line  50  branches through a reducing valve  49  from the oil line  30 . The pilot oil line  50  is connected to controls of the selector valves  31   a - 34   a,    36   a,    37   a,    42   a,    44   a,    47   a  and  48   a.  Solenoid operated valves  31   b,    32   b,    33   b,    34   b,    36   b,    37   b,    42   b,    44   b,    47   b  and  48   b  are connected to the controls. The solenoid operated valves  31   b - 34   b,    36   b,    37   b,    42   b,    44   b,    47   b  and  48   b  are biased by springs to drain positions (disengaging positions). When the solenoid operated valves  31   b - 34   b,    36   b,    37   b,    42   b,    44   b,    47   b  and  48   b  are operated to supply positions, pilot pressure is supplied to the controls of the selector valves  31   a - 34   a,    36   a,    37   a,    42   a,    44   a,    47   a  and  48   a,  to operate the selector valves  31   a - 34   a,    36   a,    37   a,    42   a,    44   a,    47   a  and  48   a  to supply positions (engaging positions). 
   [3] 
   A construction for operating the forward and backward clutches  5  and  6  and first and second main speed change devices  10  and  11  will be described next. 
   As shown in  FIG. 3 , a switch valve  51  is provided for draining pilot pressure oil from the controls of the selector valves  36   a  and  37   a.  The switch valve  51  is biased to a closed position by a spring, and a clutch pedal  52  is provided for operating the switch valve  51  to an open position. As shown in  FIG. 2 , a forward and backward switching lever  59  extends from a base of a steering wheel  58  for steering the front wheels  19 . The switching lever  59  is operable to a forward position F, a backward position R and a neutral position N. 
   As shown in  FIG. 2 , the shift lever  28  is supported to be rockable about a transverse axis on a driving platform of the vehicle body. The shift lever  28  is mechanically linked by a link mechanism  55  to a shift rod  54  for sliding the shift element  53  of the auxiliary speed change device  12 . The shift lever  28  is operable to a neutral position N, a low-speed position L and a high-speed position H, to operate the auxiliary speed change device  12  (shift element  53 ) to a neutral position, a low-speed position and a high-speed position. A position sensor  70  is provided for detecting the operated positions of the shift lever  28 . An up-shift button  61  (corresponding to a manual shifter) and a down-shift button  62  (corresponding to a manual shifter) are arranged vertically on the left side of the shift lever  28 . When the up-shift button  61  and down-shift button  62  are pushed, the first and second main speed change devices  10  and  11  are operated as described in section [6] hereinafter. 
   As shown in  FIG. 2 , the driving platform includes a seven-segment speed indicator  64  for indicating shift positions (first to eighth speeds) of the first and second main speed change devices  10  and  11 , a forward lamp  65  and a backward lamp  66  for indicating which of the forward and backward clutches  5  and  6  is engaged, and a neutral lamp  67  for indicating that the shift lever  28  or forward and backward switching lever  59  is in the neutral position N. As shown in  FIG. 3 , pressure sensors  74  are provided for detecting a working pressure of the forward and the backward clutches  5  and  6 , and the forward lamp  65  and backward lamp  66  are lit based on detection by the pressure sensor  74 . 
   As shown in  FIG. 2 , a setting switch  68  (corresponding to a manual selector) is provided to be manually operable. The setting switch  68  is operable to three positions including a manual mode position shown in  FIG. 2 , a run mode position when pushed in a D 1  direction, and a load mode position when pushed in a D 2  direction. When the setting switch  68  is pushed to the manual mode position, run mode position and load mode position, a manual mode, a run mode (corresponding to the automatic mode) and a load mode (corresponding to the automatic mode) are set as described in sections [6], [7], [8] and [9] hereinafter. 
   [4] 
   Next, operation of the forward and backward switching lever  59  will be described with reference to  FIG. 4 . 
   When the forward and backward switching lever  59  is operated to the forward position F (step S 1 ), a control current is supplied to the solenoid controlled valve  36   b  to operate the selector valve  36   a  to the supply position, which engages the forward clutch  5  (step S 2 ) and lights the forward lamp  65  (step S 3 ). When the forward and backward switching lever  59  is operated to the backward position R (step S 1 ), the control current is supplied to the solenoid controlled valve  37   b  to operate the selector valve  37   a  to the supply position, which engages the backward clutch  6  (step S 4 ), lights the backward lamp  66  (step S 5 ), and intermittently sounds a buzzer  71  shown in  FIG. 2  (step S 6 ). 
   When the forward and backward switching lever  59  is operated to the neutral position N (step S 1 ), the control current to the solenoid controlled valves  36   b  and  37   b  is stopped to operate the selector valves  36   a  and  37   a  to the drain positions, which disengages the forward and backward clutches  5  and  6  (step S 7 ) and lights the neutral lamp  67  (step S 8 ). When the clutch pedal  52  is depressed, the switch valve  51  is operated to the open position to operate the selector valves  36   a  and  37   a  to the drain positions, which disengages the forward and backward clutches  5  and  6 , and lights the neutral lamp  67 . When both of the forward and backward clutches  5  and  6  are disengaged as above, power transmission through the forward and backward clutches  5  and  6  is broken to stop the vehicle body. 
   [5] 
   Next, operation of the auxiliary speed change device  12  by the shift lever  28  will be described. 
   When the shift lever  28  is operated to the neutral position N, the auxiliary speed change device  12  (shift element  53 ) is operated to the neutral position. When the shift lever  28  is operated to the low-speed position L, the auxiliary speed change device  12  (shift element  53 ) is operated to the low-speed position. When the shift lever  28  is operated to the high-speed position H, the auxiliary speed change device  12  (shift element  53 ) is operated to the high-speed position. 
   When, for example, the shift lever  28  is operated to the neutral position N, with the forward and backward switching lever  59  operated to the forward position F (i.e. with the forward clutch  5  engaged, and the backward clutch  6  disengaged), the selector valve  36   a  is operated to the drain position by the solenoid controlled valve  36   b,  based on the detection by the position sensor  70 , to disengage the forward clutch  5 . 
   Subsequently, when the shift lever  28  is operated to the low-speed position L (or high-speed position H), the selector valve  36   a  is operated to the supply position by the solenoid controlled valve  36   b,  based on the detection of the position sensor  70 , and the forward clutch  5  is gradually engaged by the electromagnetic proportional valve  35 . 
   When the shift lever  28  is operated to the neutral position N and to the low-speed position L (or high-speed position H) as described above, with the forward and backward switching lever  59  operated to the backward position R (i.e. with the backward clutch  6  engaged, and the forward clutch  5  disengaged), the backward clutch  6  is disengaged and then engaged, as is the forward clutch  5 . 
   [6] 
   Next, a state where the setting switch  68  is pushed to the manual mode position will be described with reference to  FIG. 5  (this corresponding to the manual speed change device). 
   When the setting switch  68  is pushed to the manual mode position, the manual mode is set. As shown in  FIG. 1 , the first main speed change device  10  can provide four speeds, and the second main speed change device  11  can provide two speeds. Thus, the first and second main speed change devices  10  and  11  together can provide eight speeds. When the low-speed clutch  26  is engaged, the first to fourth speed clutches  21 - 24  correspond to shift positions for the first to fourth speeds. When the high-speed clutch  27  is engaged, the first to fourth speed clutches  21 - 24  correspond to shift positions for the fifth to eighth speeds. 
   As shown in  FIGS. 2 and 3 , the first to fourth speed clutches  21 - 24  and the low-speed and high-speed clutches  26  and  27  have pressure sensors  63  and  74  for detecting working pressure, respectively. The pressure sensors  63  and  74  detect a current shift position of the first and second main speed change devices  10  and  11  (i.e. one of the first to eighth speeds). The shift position detected of the first and second main speed change devices  10  and  11  is displayed on the speed indicator  64 . 
   Assume that, in the above state, the up-shift button  61  or down-shift button  62  is pushed (steps S 11  and S 12 ). When the up-shift button  61  is pushed (step S 11 ), as shown in a solid line A 1  (point of time B 1 ) in  FIG. 6 , one of the first to fourth speed clutches  21 - 24  next higher than the current shift position of the first and second main speed change devices  10  and  11  begins to be engaged by a corresponding one of the solenoid controlled valves  31   b - 34   b  (step S 13 ). When the down-shift button  62  is pushed (step S 12 ), one of the first to fourth speed clutches  21 - 24  next lower than the current shift position of the first and second main speed change devices  10  and  11  begins to be engaged by a corresponding one of the solenoid controlled valves  31   b - 34   b  (step S 14 ). 
   When the shift lever  28  is in the low-speed position L or high-speed position H (step S 15 ), substantially simultaneously with steps S 13  and S 14 , as shown in a solid line A 2  (point of time B 1 ) in  FIG. 6 , the working pressure of the low-speed or high-speed clutch  26  or  27  engaged is lowered from the working pressure P 2  for engagement to a predetermined low pressure P 3  by the electromagnetic proportional valve  38  or  39  (step S 16 ). When a change is made in this case from the shift position for the fourth speed to the shift position for the fifth speed, the working pressure of the low-speed clutch  26  is reduced to zero, and the working pressure of the high-speed clutch  27  is raised from zero to the predetermined low pressure P 3 . Conversely, when a change is made from the shift position for the fifth speed to the shift position for the fourth speed, the working pressure of the high-speed clutch  27  is reduced to zero, and the working pressure of the low-speed clutch  26  is raised from zero to the predetermined low pressure P 3 . 
   As shown in the solid line A 1  (from point of time B 2  to point of time B 3 ) in  FIG. 6 , the working pressure of the next higher or lower one of the first to fourth speed clutches  21 - 24  begins to be raised by one of the solenoid controlled valves  31   b - 34   b  to the working pressure P 1  for engagement. Simultaneously, as shown in a long dashed short dashed line A 3  (from point of time B 2  to point of time B 3 ) in  FIG. 6 , the working pressure of one of the first to fourth speed clutches  21 - 24  operative before the up-shift button  61  or down-shift button  62  was pressed begins to be lowered by one of the solenoid controlled valves  31   b - 34   b  from the working pressure P 1  for engagement to zero (step S 17 ). 
   When the shift lever  28  is in the low-speed position L or high-speed position H (step S 18 ), as shown in the solid line A 2  (from point of time B 3  to point of time B 4 ) in  FIG. 6 , the working pressure of the low-speed or high-speed clutch  26  or  27  is gradually raised from the predetermined low pressure P 3  by the electromagnetic proportional valve  38  or  39  (step S 19 ). As a result, power begins to be transmitted from the next higher or lower one of the first to fourth speed clutches  21 - 24  through the low-speed or high-speed clutch  26  or  27 . When the pressure sensor  63  detects the working pressure of the low-speed or high-speed clutch  26  or  27  having reached the working pressure P 2  for engagement as at point of time B 4  of the solid line A 2  in  FIG. 6  (step S 20 ), it is determined that the shifting operation based on the pushing of the up-shift button  61  or down-shift button  62  is completed. A speed position of the first and second main speed change devices  10  and  11  resulting from the shifting operation is displayed on the speed indicator  64  (step S 21 ). The buzzer  71  is sounded once to inform the operator of the end of the shifting operation (step S 22 ). Then, the operation moves to step S 11  to be ready for a next shifting operation based on pushing of the up-shift button  61  or down-shift button  62 . 
   When the shift lever  28  is in the neutral position N (steps S 15  and S 18 ), the auxiliary speed change device  12  (shift element  53 ) is operated to the neutral position, and the vehicle stands still. When the up-shift button  61  or down-shift button  62  is pushed, with the shift lever  28  placed in the neutral position N (steps S 11  and S 12 ), the first and second main speed change devices  10  and  11  (first to fourth speed clutches  21 - 24 , and the low-speed and high-speed clutches  26  and  27 ) are operated for a one-step higher or lower speed as described above (steps S 13 , S 14  and S 17 ). A speed position of the first and second main speed change devices  10  and  11  resulting from the shifting operation is displayed on the speed indicator  64  (step S 21 ), and the buzzer  71  is sounded once (step S 22 ). 
   In this case, since the vehicle is standing still, the operation for changing the working pressure of the low-speed or high-speed clutch  26  or  27  to the predetermined low pressure P 3  as in steps S 16  and S 19  is not carried out, nor the operation for changing to the working pressure P 2  for engagement (steps S 15  and S 18 ). 
   [7] 
   Next, a state where the setting switch  68  is pushed to the load mode position will be described with reference to  FIG. 7 . 
   When the setting switch  68  is pushed to the load mode position, the load mode is set. In the load mode in which the vehicle engages in a cultivating operation with a plow (not shown), a subsoiler (not shown) or the like, the first and second main speed change devices  10  and  11  are automatically operated to a low speed side and a high speed side in an automatic shifting range R of the load mode as described hereinafter according to ups and downs of an operating ground, variations in soil texture and so on. 
   As shown in  FIGS. 1 and 2 , a hand accelerator lever  73  is provided to be manually operable to set an accelerator opening for the engine  1 , and an opening sensor  75  of the potentiometer type is provided for detecting an operative position of the hand accelerator lever  73 . Further, a rotational frequency sensor  72  is provided for detecting an actual number of rotations N 2  of the engine  1 . A relationship is determined in advance between the number of rotations of the engine  1  in unloaded condition (i.e. a state in which the engine  1  is free from a load, with the forward and backward clutches  5  and  6  are disengaged, and the PTO clutch  3  is disengaged) and detection value of the opening sensor  75  (i.e. operative position of the hand accelerator lever  73 ). From the detection value of the opening sensor  75  (operative position of the hand accelerator lever  73 ), the number of rotations of the engine  1  in the unloaded condition is determined as a set number of rotations N 1  of the engine  1  (step S 31 ). 
   As described in section [12] hereinafter, the automatic shifting range R of the load mode is set to two stages, three stages or four stages. A shift position of the first and second main speed change devices  10  and  11  in time of the setting switch  68  being pushed to the load mode position is set as a high speed limit position RH in the automatic shifting range R of the load mode (step S 32 ). The shift position of the first and second main speed change devices  10  and  11  (the high speed limit position RH in the automatic shifting range R of the load mode) is displayed on the speed indicator  64  (step S 33 ), and the speed indicator  64  is lit (step S 34 ). 
   After step S 32 , a low speed limit position RL in the automatic shifting range R of the load mode is set based on the width of the automatic shifting range R of the load mode described in section [12] hereinafter (step S 35 ). When, for example, the fourth speed position is set as the high speed limit position RH of the automatic shifting range R of the load mode, and the width of the automatic shifting range R of the load mode is three stages, the second speed position is set as the low speed limit position RL of the automatic shifting range R of the load mode. In this case, where the low speed limit position RL of the automatic shifting range R of the load mode becomes lower than the first speed position (step S 36 ), the first speed position is set as the low speed limit position RL of the automatic shifting range R of the load mode (step S 37 ). 
   The actual number of rotations N 2  of the engine  1  is detected (step S 38 ), and a difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  is determined (step S 39 ). When the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  is large, it can be determined that a large load is acting on the engine  1  and has greatly reduced the actual number of rotations N 2  of the engine  1 . When the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  is small, it can be determined that a small load is acting on the engine  1  and has little reduced the actual number of rotations N 2  of the engine  1 . 
   As shown in  FIG. 13 , a first preset value N 11  and a second preset value N 12  are set for the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1 . When the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  is greater than the first preset value N 11  (step S 40 ), it can be determined that the actual number of rotations N 2  of the engine  1  has reduced greatly. Then, steps S 14 , S 16 , S 17  and S 19  in  FIG. 5  are executed to operate the first and second main speed change devices  10  and  11  for a next lower speed (step S 43 ). 
   In this case, when the set number of rotations N 1  of the engine  1  is less than the preset value N 23  (e.g. 1,300 rpm) (step S 41 ), or a shift position of the first and second main speed change devices  10  and  11  prior to the above operation is the low speed limit position RL in the automatic shifting range R of the load mode (step S 42 ), the first and second main speed change devices  10  and  11  are not operated for the next lower speed, but are retained in the shift position prior to the above operation. 
   When the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  becomes less than the second preset value N 12  (step S 40 ), it can be determined that the actual number of rotations N 2  of the actual engine  1  has little reduced. Then, steps S 13 , S 16 , S 17  and S 19  in  FIG. 5  are executed to operate the first and second main speed change devices  10  and  11  for a next higher speed (step S 46 ). 
   In this case, when the set number of rotations N 1  of the engine  1  is less than the preset value N 26  (e.g. 1,600 rpm) (step S 44 ), or a shift position of the first and second main speed change devices  10  and  11  prior to the above operation is the high speed limit position RH in the automatic shifting range R of the load mode (step S 45 ), the first and second main speed change devices  10  and  11  are not operated for the next higher speed, but are retained in the shift position prior to the above operation. 
   After steps S 40 -S 46 , the shift position of the first and second main speed change devices  10  and  11  is displayed on the speed indicator  64  (step S 47 ). In this case, when the shift position of the first and second main speed change devices  10  and  11  is the high-speed limit position RH in the automatic shifting range R of the load mode, the speed indicator  64  is lit (steps S 48  and S 49 ). When the shift position of the first and second main speed change devices  10  and  11  is not the high-speed limit position RH in the automatic shifting range R of the load mode, the speed indicator  64  is blinked (steps S 48  and S 50 ). 
   In the load mode, as described above, based on the set number of rotations N 1  of the engine  1 , the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1 , and the first and second preset values N 11  and N 12 , the first and second main speed change devices  10  and  11  are automatically operated to the low speed side or high speed side in the automatic shifting range R of the load mode (the above corresponding to the automatic shifting device). 
   In this case, when the shift lever  28  is operated from the low-speed position L to the high-speed position H or from the high-speed position H to the low-speed position L, or when the setting switch  68  is pushed to the load mode position once again, with the first and second main speed change devices  10  and  11  automatically operated to the low speed side or high speed side in the automatic shifting range R of the load mode, the shift position of the first and second main speed change devices  10  and  11  is set again as the high-speed limit position RH in the automatic shifting range R of the load mode, and the operation moves to step S 33 . 
   [8] 
   Next, the first half of a state where the setting switch  68  is pushed to the run mode position will be described with reference to  FIG. 8 . 
   When the setting switch  68  is pushed to the run mode position, the run mode is set. In the run mode in which the vehicle engages in a running operation towing a trailer (not shown) or the like, the first and second main speed change devices  10  and  11  are automatically operated to a low speed side and a high speed side in an automatic shifting range R of the run mode as described hereinafter according to operation of the hand accelerator lever  73  or variations in the actual number of rotations N 2  of the engine  1  in an uphill run. 
   As in the load mode described in section [7] above, from the detection value of the opening sensor  75  (operative position of the hand accelerator lever  73 ), the number of rotations of the engine  1  in the unloaded condition is determined as a set number of rotations N 1  of the engine  1  (step S 51 ). As described in section [12] hereinafter, the automatic shifting range R of the run mode is set to two stages, three stages or four stages. A shift position of the first and second main speed change devices  10  and  11  in time of the setting switch  68  being pushed to the run mode position is set as a high speed limit position RH in the automatic shifting range R of the run mode (step S 52 ). The shift position of the first and second main speed change devices  10  and  11  (the high speed limit position RH in the automatic shifting range R of the run mode) is displayed on the speed indicator  64  (step S 53 ), and the speed indicator  64  is lit (step S 54 ). 
   After the high speed limit position RH in the automatic shifting range R of the run mode is set, a low speed limit position RL in the automatic shifting range R of the run mode is set based on the width of the automatic shifting range R of the run mode described in section [12] hereinafter (step S 55 ). When, for example, the fourth speed position is set as the high speed limit position RH of the automatic shifting range R of the run mode, and the width of the automatic shifting range R of the run mode is three stages, the second speed position is set as the low speed limit position RL of the automatic shifting range R of the run mode. In this case, where the low speed limit position RL of the automatic shifting range R of the run mode becomes lower than the first speed position (step S 56 ), the first speed position is set as the low speed limit position RL of the automatic shifting range R of the run mode (step S 57 ). 
   The actual number of rotations N 2  of the engine  1  is detected (step S 58 ), and a difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  is determined (step S 59 ). When the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  is large, it can be determined that a large load is acting on the engine  1  and has greatly reduced the actual number of rotations N 2  of the engine  1 . 
   As shown in  FIG. 13 , the first preset value N 11  is set for the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1 . When the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  is greater than the first preset value N 11  (step S 60 ), it can be determined that the actual number of rotations N 2  of the engine  1  has reduced greatly. Then, steps S 14 , S 16 , S 17  and S 19  in  FIG. 5  are executed to operate the first and second main speed change devices  10  and  11  for a next lower speed (step S 63 ). 
   In this case, when the set number of rotations N 1  of the engine  1  is less than the preset value N 23  (e.g. 1,300 rpm) (step S 61 ), or a shift position of the first and second main speed change devices  10  and  11  prior to the above operation is the low speed limit position RL in the automatic shifting range R of the run mode (step S 62 ), the first and second main speed change devices  10  and  11  are not operated for the next lower speed, but are retained in the shift position prior to the above operation. 
   After steps S 60 -S 63 , the shift position of the first and second main speed change devices  10  and  11  is displayed on the speed indicator  64  (step S 64 ). In this case, when the shift position of the first and second main speed change devices  10  and  11  is the high-speed limit position RH in the automatic shifting range R of the run mode, the speed indicator  64  is lit (steps S 65  and S 66 ). When the shift position of the first and second main speed change devices  10  and  11  is not the high-speed limit position RH in the automatic shifting range R of the run mode, the speed indicator  64  is blinked (steps S 65  and S 67 ). 
   [9] 
   Next, the second half of the state where the setting switch  68  is pushed to the run mode position will be described with reference to  FIGS. 8 and 9 . 
   When, in step S 60  described in section [8] above, the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  is less than the first preset value N 11 , and the hand accelerator lever  73  is not operated (step S 68 ), the first and second main speed change devices  10  and  11  are not operated. 
   When, in step S 60  described in section [8] above, the hand accelerator lever  73  is operated to a high rotation side at low speed (step S 68 ), the set number of rotations N 1  of the engine  1  is less than a preset value N 28  (e.g. 2,400 rpm) (step S 69 ), the set number of rotations N 1  of the engine  1  is equal to or greater than a preset value N 22  (e.g. 1,200 rpm) and less than a preset value N 24  (e.g. 1,400 rpm) (step S 70 ), and the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  becomes less than a preset value N 4  (e.g. 100 rpm) (step S 73 ), steps S 13 , S 16 , S 17  and S 19  in  FIG. 5  are executed to operate the first and second main speed change devices  10  and  11  for a next higher speed (step S 75 ). 
   Next, when the set number of rotations N 1  of the engine  1  is equal to or greater than the above preset value N 24  (e.g. 1,400 rpm) and less than the preset value N 26  (e.g. 1,600 rpm) (step S 71 ), and the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  becomes less than the preset value N 4  (e.g. 100 rpm) (step S 73 ), steps S 13 , S 16 , S 17  and S 19  in  FIG. 5  are executed to operate the first and second main speed change devices  10  and  11  for a further higher speed (step S 75 ). Next, when the set number of rotations N 1  of the engine  1  is equal to or greater than the preset value N 26  (e.g. 1,600 rpm) and less than the preset value N 28  (e.g. 2,400 rpm) (step S 72 ), and the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  becomes less than the preset value N 4  (e.g. 100 rpm) (step S 73 ), steps S 13 , S 16 , S 17  and S 19  in  FIG. 5  are executed to operate the first and second main speed change devices  10  and  11  for a still higher speed (step S 75 ). 
   When, in step S 60  described in section [8] above, the hand accelerator lever  73  is operated to the high rotation side at high speed (step S 68 ), the set number of rotations N 1  of the engine  1  is equal to or greater than the preset value N 28  (e.g. 2,400 rpm) (step S 76 ), and the actual number of rotations N 2  of the engine  1  is equal to or greater than a preset value N 21  (e.g. 1,100 rpm) and less than a preset value N 23  (e.g. 1,300 rpm) (step S 77 ), steps S 13 , S 16 , S 17  and S 19  in  FIG. 5  are executed to operate the first and second main speed change devices  10  and  11  for a next higher speed (step S 75 ). Next, when the actual number of rotations N 2  of the engine  1  becomes equal to or greater than the preset value N 23  (e.g. 1,300 rpm) and less than a preset value N 25  (e.g. 1,500 rpm) (step S 78 ), steps S 13 , S 16 , S 17  and S 19  in  FIG. 5  are executed to operate the first and second main speed change devices  10  and  11  for a further higher speed (step S 75 ). 
   Next, when the actual number of rotations N 2  of the engine  1  becomes equal to or greater than the set number of rotations N 1  (e.g. 1,500 rpm) of the engine  1  and less than a preset value N 27  (e.g. 2,300 rpm) (step S 79 ), steps S 13 , S 16 , S 17  and S 19  in  FIG. 5  are executed to operate the first and second main speed change devices  10  and  11  for a still higher speed (step S 75 ). Next, when the set actual number of rotations N 2  of the engine  1  is equal to or greater than the preset value N 27  (e.g. 2,300 rpm) (step S 80 ), steps S 13 , S 16 , S 17  and S 19  in  FIG. 5  are executed to operate the first and second main speed change devices  10  and  11  for a still higher speed (step S 75 ). 
   In this case, when, in steps S 68 -S 73  and S 76 -S 80 , the shift position of the first and second main speed change devices  10  and  11  prior to the operation is the high-speed limit position RH in the automatic shifting range R of the run mode (step S 74 ), the first and second main speed change devices  10  and  11  are not operated for a next higher speed, but are retained in the shift position prior to the operation. After the above steps S 68 -S 80 , the operation moves to step S 64  in  FIG. 8 . 
   In the run mode, as described in sections [8] and [9] above, based on the set number of rotations N 1  of the engine  1 , the actual number of rotations N 2  of the engine  1 , the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1 , the first preset value N 11 , and operation of the hand accelerator lever  73 , the first and second main speed change devices  10  and  11  are automatically operated to the low speed side or high speed side in the automatic shifting range R of the run mode (the above corresponding to the automatic shifting device). 
   In this case, when the shift lever  28  is operated from the low-speed position L to the high-speed position H or from the high-speed position H to the low-speed position L, or when the setting switch  68  is pushed to the run mode position once again, with the first and second main speed change devices  10  and  11  automatically operated to the low speed side or high speed side in the automatic shifting range R of the run mode, the shift position of the first and second main speed change devices  10  and  11  is set again as the high-speed limit position RH in the automatic shifting range R of the run mode, and the operation moves to step S 53  in  FIG. 8 . 
   [10] 
   Operation for setting the first and second preset values N 11  and N 12  (see sections [7], [8] and [9] above) by a sensitivity adjusting switch  76  will be described next. 
   A dial type sensitivity adjusting switch  76  is provided as shown in  FIG. 2 . The sensitivity adjusting switch  76  is operable to set the first preset value N 11  (solid line A 4 ) and second preset value N 12  (solid line A 5 ) as shown in  FIG. 13 . The first preset value N 11  (solid line A 4 ) and second preset value N 12  (solid line A 5 ) determine an “operating range for the high speed side”, a “standard range” and an “operating range for the low speed side”. 
   Thus, when, as described in sections [7], [8] and [9] above, the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  becomes equal to or greater than the first preset value N 11  “operating range for the low speed side”, the first and second main speed change devices  10  and  11  are operated for a next lower speed. When the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  is between the first and second preset values N 11  and N 12  (“standard region”), the first and second main speed change devices  10  and  11  are not operated for a lower speed and higher speed. When the difference N 3  between the set number of rotations N 1  of the engine  1  and the actual number of rotations N 2  of the engine  1  becomes less than the second preset value N 12  “operating range for the high speed side”, the first and second main speed change devices  10  and  11  are operated for a next higher speed. 
   As shown in  FIG. 13 , when the sensitivity adjusting switch  76  is in an operation range H 1 , the first preset value N 11  is maintained at “N 35 ” (“N 35 ” means a value shown by N 35 ), and the second preset value N 12  at “N 33 ”. When the sensitivity adjusting switch  76  is in an operation range H 2 , the first preset value N 11  remains at “N 35 ”, but the second preset value N 12  is changed linearly in a small range between “N 33 ” and “N 34 ” according to an operative position of the sensitivity adjusting switch  76 . In this case, the values are in a relationship N 33 &lt;N 34 &lt;N 35 . 
   As shown in  FIG. 13 , when the sensitivity adjusting switch  76  is in an operation range H 3 , the second preset value N 12  is changed linearly in a range between “N 31 ” and “N 33 ” according to an operative position of the sensitivity adjusting switch  76 . In this case, the values are in a relationship N 31 &lt;N 33 . The difference between “N 31 ” and “N 33 ” is larger than that between “N 33 ” and “N 34 ” (the rate of change of the second preset value N 12  (solid line A 5 ) is higher in the operation range H 3  than in the operation range H 2 ). 
   As shown in  FIG. 13 , when the sensitivity adjusting switch  76  is in an operation range H 4 , the second preset value N 12  is set to “0”. Thus, with the sensitivity adjusting switch  76  is in the operation range H 4  and the second preset value N 12  set to “0”, the first and second main speed change devices  10  and  11  are not operated to the high speed side. 
   As shown in  FIG. 13 , when the sensitivity adjusting switch  76  is in the operation ranges H 3  and H 4 , the first preset value N 11  is changed linearly in a range between “N 32 ” and “N 35 ” according to an operative position of the sensitivity adjusting switch  76 . In this case, the values are in a relationship 0&lt;N 31 &lt;N 32 &lt;N 33 &lt;N 34 &lt;N 35 . The difference between “N 32 ” and “N 35 ” is larger than those between “N 33 ” and “N 34 ” and between “N 31 ” and “N 33 ” (the rate of change of the first preset value N 11  (solid line A 4 ) in the operation ranges H 3  and H 4  is higher than those of the second preset value N 12  (solid line A 5 ) in the operation range H 2  and operation range H 3 ). 
   [11] 
   A first automatic deceleration control and a second automatic deceleration control performed in the load mode and run mode described in sections [7], [8] and [9] hereinbefore will be described next. 
   The agricultural tractor has lift arms (not shown) at the rear of the vehicle body for raising and lowering a link mechanism (not shown). A working implement (e.g. a plough, subsoilder or rotary tiller) is connected to the link mechanism. The tractor makes a turn at an end of an operating field with the working implement raised from the ground. 
   When a manual control device (not shown) for operating the lift arms (e.g. a lift lever or lift switch) is operated to raise the lift arm or when the lift arms are in an upper limit position of a range of vertical movement, in the load mode (run mode) described in sections [7], [8] and [9] hereinbefore, the operation to the high speed side of the first and second speed change devices  10  and  11  is prohibited, and the first and second speed change devices  10  and  11  are operated to the low speed side by a first predetermined deceleration number of speeds (see section [12] hereinafter) in the automatic shifting range R of the load mode (run mode) (the above corresponding to the first automatic deceleration control). 
   In this case, where the first predetermined deceleration number of speeds requires the first and second speed change devices  10  and  11  to be operated to the low speed side beyond the low speed limit position RL in the automatic shifting range R of the load mode (run mode), the decelerating operation of the first and second speed change devices  10  and  11  will stop at the low speed limit position RL in the automatic shifting range R of the load mode (run mode). 
   Assume, for example, the hand accelerator lever  73  is operated to the low rotation side in time of vehicle turning or slowdown, the set number of rotations N 1  of the engine  1  is less than a preset value (e.g. 1,000 rpm), and the actual number of rotations N 2  of the engine  1  is less than a preset value (e.g. 2,300 rpm). In this case, the first and second speed change devices  10  and  11  are operated to the low speed side by a second predetermined deceleration number of speeds (see section [12] hereinafter) in the automatic shifting range R of the load mode (run mode) (the above corresponding to the second automatic deceleration control). 
   In this case, where the second predetermined deceleration number of speeds requires the first and second speed change devices  10  and  11  to be operated to the low speed side beyond the low speed limit position RL in the automatic shifting range R of the load mode (run mode), the decelerating operation of the first and second speed change devices  10  and  11  will stop at the low speed limit position RL in the automatic shifting range R of the load mode (run mode). 
   [12] 
   A state of setting the width of the automatic shifting range R of the load mode (run mode) described in sections [7], [8] and [9] hereinbefore to two speeds, three speeds or four speeds, and a state of setting the first and second predetermined deceleration numbers of speeds for the first and second automatic deceleration controls described in section [11] above, will be described next with reference to  FIG. 10 . 
   When, with the shift lever  28  placed in the neutral position N, and after pushing the setting switch  68  to the load mode position (in D 2  direction), a long pushing operation E 1  (e.g. three seconds or longer) of the setting switch  68  is effected in D 2  direction, the buzzer  71  sounds once, and the speed indicator  64  blinks while displaying “L” indicating a setting mode for the load mode (step S 81 ). In this state, the setting mode for the load mode remains unestablished. A pushing operation E 2  in D 2  direction of the setting switch  64  causes the speed indicator  64  to blink while displaying “P” indicating a setting mode for the first automatic deceleration control (step S 82 ) (the setting mode for the first automatic deceleration control also being unestablished). 
   In the state noted above where the setting mode for the load mode is unestablished (step S 81 ) and the setting mode for the first automatic deceleration control also unestablished (step S 82 ), each pushing operation E 2  in D 2  direction of the setting switch  64  causes an alternate display of the unestablished state of the setting mode for the load mode (step S 81 ) and the unestablished state of the setting mode for the first automatic deceleration control (step S 82 ). 
   When, in the state noted above where the setting mode for the load mode is unestablished (step S 81 ), a long pushing operation E 3  (e.g. three seconds or longer) of the setting switch  68  is effected in D 2  direction, the buzzer  71  sounds once, and the setting mode for the load mode is established (step S 83 ). In step S 83 , the speed indicator  64  blinks while displaying “2”. Each pushing operation E 4  in D 2  direction of the setting switch  64  causes the speed indicator  64  to repeat in cycles the state of blinking while displaying “2”, a state of blinking while displaying “3” and a state of blinking while displaying “4”. 
   When, in step S 83 , a long pushing operation E 5  (e.g. three seconds or longer) of the setting switch  68  is effected in D 2  direction, the buzzer  71  sounds once, the number (“2”, “3” or “4”) then displayed on the speed indicator  64  is set as the width of the automatic shifting range R of the load mode, and the speed indicator  64  becomes a continuously lit state (step S 84 ). 
   When, in the state noted above where the setting mode for the first automatic deceleration control is unestablished (step S 82 ), a long pushing operation E 6  (e.g. three seconds or longer) of the setting switch  68  is effected in D 2  direction, the buzzer  71  sounds once, and the setting mode for the first automatic deceleration control is established (step S 85 ). In step S 85 , the speed indicator  64  blinks while displaying “0”. Each pushing operation E 7  in D 2  direction of the setting switch  64  causes the speed indicator  64  to repeat in cycles the state of blinking while displaying “0”, a state of blinking while displaying “1”, a state of blinking while displaying “2” and a state of blinking while displaying “3”. 
   When, in step S 85 , a long pushing operation E 8  (e.g. three seconds or longer) of the setting switch  68  is effected in D 2  direction, the buzzer  71  sounds once, the number (“0”, “1”, “2” or “3”) then displayed on the speed indicator  64  is set as the first predetermined deceleration number of speeds, and the speed indicator  64  becomes a continuously lit state (step S 86 ). In this case, when “0” is set as the first predetermined deceleration number of speeds, the first automatic deceleration control will not be performed. 
   When, with the shift lever  28  placed in the neutral position N, and after pushing the setting switch  68  to the run mode position (in D 1  direction), a long pushing operation E 9  (e.g. three seconds or longer) of the setting switch  68  is effected in D 1  direction, the buzzer  71  sounds once, and the speed indicator  64  blinks while displaying “r” indicating a setting mode for the run mode (step S 87 ). In this state, the setting mode for the run mode remains unestablished. A pushing operation E 10  in D 1  direction of the setting switch  64  causes the speed indicator  64  to blink while displaying “A” indicating a setting mode for the second automatic deceleration control (step S 88 ) (the setting mode for the second automatic deceleration control also being unestablished). 
   In the state noted above where the setting mode for the run mode is unestablished (step S 87 ) and the setting mode for the second automatic deceleration control also unestablished (step S 88 ), each push operation E 10  in D 1  direction of the setting switch  64  causes an alternate display of the unestablished state of the setting mode for the run mode (step S 87 ) and the unestablished state of the setting mode for the second automatic deceleration control (step S 88 ). 
   When, in the state noted above where the setting mode for the run mode is unestablished (step S 87 ), a long pushing operation E 11  (e.g. three seconds or longer) of the setting switch  68  is effected in D 1  direction, the buzzer  71  sounds once, and the setting mode for the run mode is established (step S 89 ). In step S 89 , the speed indicator  64  blinks while displaying “2”. Each pushing operation E 12  in D 1  direction of the setting switch  64  causes the speed indicator  64  to repeat in cycles the state of blinking while displaying “2”, a state of blinking while displaying “3” and a state of blinking while displaying “4”. 
   When, in step S 89 , a long pushing operation E 13  (e.g. three seconds or longer) of the setting switch  68  is effected in D 1  direction, the buzzer  71  sounds once, the number (“2”, “3” or “4”) then displayed on the speed indicator  64  is set as the width of the automatic shifting range R of the run mode, and the speed indicator  64  becomes a continuously lit state (step S 90 ). 
   When, in the state noted above where the setting mode for the second automatic deceleration control is unestablished (step S 88 ), a long pushing operation E 14  (e.g. three seconds or longer) of the setting switch  68  is effected in D 1  direction, the buzzer  71  sounds once, and the setting mode for the second automatic deceleration control is established (step S 91 ). In step S 91 , the speed indicator  64  blinks while displaying “0”. Each pushing operation E 15  in D 1  direction of the setting switch  64  causes the speed indicator  64  to repeat in cycles the state of blinking while displaying “0”, a state of blinking while displaying “1”, a state of blinking while displaying “2” and a state of blinking while displaying “3”. 
   When, in step S 91 , a long pushing operation E 16  (e.g. three seconds or longer) of the setting switch  68  is effected in D 1  direction, the buzzer  71  sounds once, the number (“0”, “1”, “2” or “3”) then displayed on the speed indicator  64  is set as the second predetermined deceleration number of speeds, and the speed indicator  64  becomes a continuously lit state (step S 92 ). In this case, when “0” is set as the second predetermined deceleration number of speeds, the second automatic deceleration control will not be performed. 
   [13] 
   The first half of changing of the automatic shifting range R of the load mode (or run mode) described in sections [7], [8] and [9] hereinbefore will be described next with reference to  FIG. 11  (the width of the automatic shifting range R of the load mode (or run mode) described in section [12] above being maintained). 
   When, with the setting switch  68  pushed to the load mode position (or run mode position) and the shift lever  28  operated to the neutral position N (step S 101 ), the up-shift button  61  is pushed (step S 102 ), the first and second main speed change devices  10  and  11  are operated for a next higher speed (step S 104 ). When the down-shift button  62  is pushed in the same state (step S 103 ), the first and second main speed change devices  10  and  11  are operated to a next lower speed (step S 105 ). In this case, operations as in steps S 13 , S 14 , S 16 , S 17  and S 19  in  FIG. 5  are not performed, One of the first to fourth speed clutches  21 - 24  providing the current speed position of the first and second main speed change devices  10  and  11  is immediately disengaged, and a different one of the first to fourth speed clutches  21 - 24  is immediately engaged to provide a next higher speed (or a next lower speed) position of the first and second main speed change devices  10  and  11 . 
   When the first and second main speed change devices  10  and  11  are operated for a next higher speed (or a next lower speed) as described above, the shift position of the first and second main speed change devices  10  and  11  resulting from the operation is set as the high speed limit position RH in the automatic shifting range R of the load mode (or run mode) (step S 106 ). The shift position of the first and second main speed change devices  10  and  11  (the high speed limit position RH in the automatic shifting range R of the load mode (or run mode)) is displayed on the speed indicator  64  (step S 107 ), and the speed indicator  64  is lit (step S 108 ). 
   When the high speed limit position RH in the automatic shifting range R of the load mode (or run mode) has been set, the low speed limit position RL in the automatic shifting range R of the load mode (or run mode) is set next based on the width of the automatic shifting range R of the load mode (or run mode) as described in section [12] hereinbefore (step S 109 ). When, for example, the fourth speed position is set as the high speed limit position RH of the automatic shifting range R of the load mode (or run mode), and the width of the automatic shifting range R of the load mode (or run mode) is three stages, the second speed position is set as the low speed limit position RL of the automatic shifting range R of the load mode (or run mode). In this case, where the low speed limit position RL of the automatic shifting range R of the load mode (or run mode) becomes lower than the first speed position (step S 110 ), the first speed position is set as the low speed limit position RL of the automatic shifting range R of the load mode (or run mode) (step S 111 ). 
   [14] 
   The second half of changing of the automatic shifting range R of the load mode (or run mode) described in sections [7], [8] and [9] hereinbefore will be described next with reference to  FIGS. 11 and 12  (the width of the automatic shifting range R of the load mode (or run mode) described in section [12] above being maintained). 
   When, with the setting switch  68  pushed to the load mode position (or run mode position) and the shift lever  28  operated to the low speed position L or high speed position H (step S 101 ), the up-shift button  61  is pushed (step S 121 ), steps S 13 , S 16 , S 17  and S 19  in  FIG. 5  are executed to operate the first and second main speed change devices  10  and  11  for a next higher speed (step S 123 ), overriding the states described in sections [7], [8] and [9] hereinbefore (the states of the first and second main speed change devices  10  and  11  being operated to the low speed side and high speed side in the automatic shifting range R of the load mode (or run mode)). 
   When the down-shift button  62  is pushed in the same state (step S 122 ), steps S 14 , S 16 , S 17  and S 19  in  FIG. 5  are executed to operate the first and second main speed change devices  10  and  11  for a next lower speed (step S 127 ), overriding the states described in sections [7], [8] and [9] hereinbefore (the states of the first and second main speed change devices  10  and  11  being operated to the low speed side and high speed side in the automatic shifting range R of the load mode (or run mode)). 
   When the up-shift button  61  and down-shift button  62  are pushed, the shift positions of the first and second main speed change devices  10  and  11  are displayed on the speed indicator  64  (step S 131 ). When the shift position of the first and second main speed change devices  10  and  11  resulting from the operation is the high speed limit position RH in the automatic shifting range R of the load mode (or run mode), the speed indicator  64  is lit (steps S 132  and S 133 ). When the shift position of the first and second main speed change devices  10  and  11  resulting from the operation is not the high speed limit position RH in the automatic shifting range R of the load mode (or run mode), the speed indicator  64  is blinked (steps S 132  and S 134 ). 
   When, with the shift position of the first and second main speed change devices  10  and  11  being the high speed limit position RH in the automatic shifting range R of the load mode (or run mode), the up-shift button  61  is pushed to operate the first and second main speed change devices  10  and  11  are operated to a next higher speed, the shift position of the first and second main speed change devices  10  and  11  will deviate to the high speed side from the automatic shifting range R of the load mode (or run mode). In such a state (steps S 121 , S 123  and S 124 ), the shift position of the first and second main speed change devices  10  and  11  resulting from the operation is set as the high speed limit position RH in the automatic shifting range R of the load mode (or run mode) (step S 125 ). 
   Next, the low speed limit position RL in the automatic shifting range R of the load mode (or run mode) is set based on the width of the automatic shifting range R of the load mode (or run mode) as described in section [12] hereinbefore (step S 126 ). When, for example, the fourth speed position is set from the third speed position as the high speed limit position RH of the automatic shifting range R of the load mode (or run mode), and the width of the automatic shifting range R of the load mode (or run mode) is three stages, the second speed position is set from the first speed position as the low speed limit position RL of the automatic shifting range R of the load mode (or run mode) (which corresponds to the state where, with the first and second main speed change devices  10  and  11  in the high speed limit position in the automatic shifting range R of the load mode (or run mode), the first and second main speed change devices  10  and  11  are operated to the high speed side whereby the entire automatic shifting range R of the load mode (or run mode) is moved to the high speed side). 
   When, with the shift position of the first and second main speed change devices  10  and  11  being the low speed limit position RL in the automatic shifting range R of the load mode (or run mode), the down-shift button  61  is pushed to operate the first and second main speed change devices  10  and  11  are operated to a next lower speed, the shift position of the first and second main speed change devices  10  and  11  will deviate to the low speed side from the automatic shifting range R of the load mode (or run mode). In such a state (steps S 122 , S 127  and S 128 ), the shift position of the first and second main speed change devices  10  and  11  resulting from the operation is set as the low speed limit position RL in the automatic shifting range R of the load mode (or run mode) (step S  129 ). 
   Next, the high speed limit position RH in the automatic shifting range R of the load mode (or run mode) is set based on the width of the automatic shifting range R of the load mode (or run mode) as described in section [12] hereinbefore (step S 126 ). When, for example, the first speed position is set from the second speed position as the low speed limit position RL of the automatic shifting range R of the load mode (or run mode), and the width of the automatic shifting range R of the load mode (or run mode) is three stages, the fourth speed position is set from the third speed position as the high speed limit position RH of the automatic shifting range R of the load mode (or run mode) (which corresponds to the state where, with the first and second main speed change devices  10  and  11  in the low speed limit position in the automatic shifting range R of the load mode (or run mode), the first and second main speed change devices  10  and  11  are operated to the low speed side whereby the entire automatic shifting range R of the load mode (or run mode) is moved to the low speed side). 
   Next, the shift position of the first and second main speed change devices  10  and  11  resulting from the operation is displayed on the speed indicator  64  (step S 131 ). When the shift position of the first and second main speed change devices  10  and  11  resulting from the operation is the high speed limit position RH in the automatic shifting range R of the load mode (or run mode), the speed indicator  64  is lit (steps S 132  and S 133 ). When the shift position of the first and second main speed change devices  10  and  11  resulting from the operation is not the high speed limit position RH in the automatic shifting range R of the load mode (or run mode), the speed indicator  64  is blinked (steps S 132  and S 134 ). 
   First Modified Embodiment 
   As shown in preceding section [10] and  FIG. 13 , when the sensitivity adjusting switch  76  is in the operation range H 4 , the second preset value N 12  is set to “0”. Instead, the second preset value N 12  (solid line A 5 ) in the operation range H 3  may be extended linearly to “0” (for example the left end of the operation range H 4  in  FIG. 13  is “0”). With this modification, even when the sensitivity adjusting switch  76  is operated to the operation range H 4 , an “operation range to the high speed side” is set. 
   Second Modified Embodiment 
   Instead of setting the first and second preset values N 11  and N 12  with one sensitivity adjusting switch  76  as described in preceding section [10], a sensitivity adjusting switch  76  for exclusive use in setting and changing the first preset value N 11  may be provided along with a sensitivity adjusting switch  76  for exclusive use in setting and changing the second preset value N 12 . In this way, the first and second preset values N 11  and N 12  may be set and changed independently of each other. 
   Third Modified Embodiment 
   The auxiliary speed change device  12  shown in  FIG. 1  may include, as does the second main speed change device  11 , a low-speed clutch (not shown) and a high-speed clutch (not shown) of the hydraulically operable multi-plate type arranged in parallel. Electromagnetic proportional valves (not shown) may be provided for the low-speed and high-speed clutches of the auxiliary speed change device  12 , respectively. With this construction, the first and second main speed change devices  10  and  11  and auxiliary speed change device  12  together provide first to 16th speeds. By pushing the up-shift button  61  and down-shift button  62 , the first and second main speed change devices  10  and  11  and auxiliary speed change device  12  may be shifted to the first to 16th speed positions. 
   Fourth Modified Embodiment 
   The first and second main speed change devices  10  and  11  shown in  FIG. 1  are constructed as the hydraulic clutch type. The first and second main speed change devices  10  and  11  may be constructed, as is the auxiliary speed change device  12 , the speed change gear type with slidable shift elements (not shown). The shift elements may be slid by hydraulic cylinders (not shown). 
   This invention is applicable also to a work vehicle with first and second main speed change devices  10  and  11  providing ten speeds or six speeds, a work vehicle with auxiliary speed change device  12  shiftable to a high-speed position, an intermediate speed position and a low-speed position, and a work vehicle with first and second main speed change devices  10  and  11  constructed as stepless transmissions of the hydrostatic type of the belt type. 
   Fifth Modified Embodiment 
   Another modified embodiment will be described next with reference to  FIG. 14 . The embodiment relates to a method of setting the width of the automatic shifting range R of the load mode (run mode) described in sections [7], [8] and [9] to two stages, three stages or four stages. 
   When, with the shift lever  28  placed in the neutral position N (step AS 81 ) and the setting switch  68  pushed to the load mode position, a long pushing operation (e.g. three seconds or longer) of the setting switch  68  is effected in D 2  direction ( FIG. 2 ) (step AS 82 ), a setting mode for the load mode is set (step AS 83 ), the buzzer  71  sounds once (step AS 84 ), and the speed indicator  64  blinks while displaying “L” indicating the setting mode for the load mode (step AS 85 ). 
   When, with the shift lever  28  placed in the neutral position N (step AS 81 ) and the setting switch  68  pushed to the run mode position, a long pushing operation (e.g. three seconds or longer) of the setting switch  68  is effected in D 1  direction ( FIG. 2 ) (step AS 82 ), a setting mode for the run mode is set (step AS 86 ), the buzzer  71  sounds once (step AS 87 ), and the speed indicator  64  blinks while displaying “d” indicating the setting mode for the run mode (step AS 88 ). 
   When the up-shift button  61  is pushed in the setting mode for the load mode or in the setting mode for the run mode as described above (step AS 89 ), the width of the automatic shifting range R is increased by one stage (e.g. from two stages to three stages) (step AS 91 ). The new width of the automatic shifting range R is displayed on the speed indicator  64  (“2”, “3” or “4”), and the speed indicator  64  blinks (step AS 93 ). When the down-shift button  62  is pushed (step AS 90 ), the width of the automatic shifting range R of the load mode (or run mode) is decreased by one stage (e.g. from three stages to two stages) (step AS 92 ). The new width of the automatic shifting range R of the load mode (or run mode) is displayed on the speed indicator  64  (“2”, “3” or “4”), and the speed indicator  64  blinks (step AS 93 ). 
   After a desired width of the automatic shifting range R of the load mode (or run mode) is obtained by pushing the up-shift button  61  and down-shift button  62 , the setting switch  68  pushed to the load mode position is further pushed long (e.g. three seconds or longer) in the D 2  direction (see  FIG. 2 ) (or the setting switch  68  pushed to the run mode position is further pushed long (e.g. three seconds or longer) in the D 1  direction (see  FIG. 2 )) (step AS 94 ). 
   As a result, the width of the automatic shifting range R of the load mode (or run mode) is set (step AS 95 ). The speed indicator  64  is lit, displaying the set width of the automatic shifting range R of the load mode (or run mode) (“2”, “3” or “4”) (step AS  96 ). The buzzer  71  is sounded once (step AS 97 ), to complete the setting mode for the load mode and the setting mode for the run mode. In this way, the width of the automatic shifting range R of the load mode (or run mode) may be set. 
   Sixth Modified Embodiment 
   The speed indicator  64 , instead of being the seven-segment type, may be the liquid crystal type including, as shown in  FIG. 15(A) , eight indicating elements  64   a,    64   b,    64   c,    64   d,    64   e,    64   f,    64   g  and  64   h  corresponding to the first to eighth speed positions. 
   In this case, the state described in section [13] (i.e. the up-shift button  61  and down-shift button  62  are pushed in the state that the setting switch  68  is pushed to the load mode position (or run mode position, and the shift lever  28  is operated to the neutral position N) is indicated by the speed indicator  64  as shown in  FIGS. 15(A)  and (B). 
   As shown in  FIG. 15(A) , for example, the first and second main speed change devices  10  and  11  are operated to the fifth speed position, and the fifth speed position of the first and second main speed change devices  10  and  11  is set as the high speed limit position RH of the automatic shifting range R of the load mode (or run mode). When the width of the automatic shifting range R of the load mode (or run mode) has three stages, the third speed position of the first and second main speed change devices  10  and  11  is the low speed limit position RL of the automatic shifting range R of the load mode (or run mode). Thus, the indicating elements  64   e,    64   d  and  64   c  of the speed indicator  64  corresponding to the fifth, fourth and third speed positions are surrounded by a different color as the automatic shifting range R of the load mode (or run mode). The indicating element  64   e  of the speed indicator  64  corresponding to the fifth speed position is lit. The other indicating elements  64   a - 64   d  and  64   f - 64   h  of the speed indicator  64  are off. 
   When the down-shift button  62  is pushed and the first and second main speed change devices  10  and  11  are operated to the fourth speed position, as shown in  FIG. 15(B) , the fourth speed position of the first and second main speed change devices  10  and  11  is set as the high speed limit position RH of the automatic shifting range R of the load mode (or run mode). The second speed position of the first and second main speed change devices  10  and  11  becomes the low speed limit position RL of the automatic shifting range R of the load mode (or run mode). Thus, the indicating elements  64   d,    64   c  and  64   b  of the speed indicator  64  corresponding to the fourth, third and second speed positions are surrounded by the different color as the automatic shifting range R of the load mode (or run mode). The indicating element  64   d  of the speed indicator  64  corresponding to the fourth speed position is lit. The other indicating elements  64   a - 64   c  and  64   e - 64   h  of the speed indicator  64  are off. 
   Seventh Modified Embodiment 
   Where the speed indicator  64  is the liquid crystal type including, as shown in  FIG. 16(A) , eight indicating elements  64   a,    64   b,    64   c,    64   d,    64   e,    64   f,    64   g  and  64   h  corresponding to the first to eighth speed positions, the state described in section [14] (i.e. the up-shift button  61  and down-shift button  62  are pushed in the state that the setting switch  68  is pushed to the load mode position (or run mode position, and the shift lever  28  is operated to the low speed position L or high speed position H) is indicated by the speed indicator  64  as shown in  FIGS. 16(A) , (B), (C), (D) and (E). 
   As shown in  FIG. 16(A) , for example, the first and second main speed change devices  10  and  11  are operated to the fifth speed position, and the fifth speed position of the first and second main speed change devices  10  and  11  is set as the high speed limit position RH of the automatic shifting range R of the load mode (or run mode). When the width of the automatic shifting range R of the load mode (or run mode) has three stages, the third speed position of the first and second main speed change devices  10  and  11  is the low speed limit position RL of the automatic shifting range R of the load mode (or run mode). Thus, the indicating elements  64   e,    64   d  and  64   c  of the speed indicator  64  corresponding to the fifth, fourth and third speed positions are surrounded by the different color as the automatic shifting range R of the load mode (or run mode). The indicating element  64   e  of the speed indicator  64  corresponding to the fifth speed position is lit. The other indicating elements  64   a - 64   d  and  64   f - 64   h  of the speed indicator  64  are off. 
   When the down-shift button  62  is pushed and the first and second main speed change devices  10  and  11  are operated to the fourth speed position, as shown in  FIG. 16(B) , the high speed limit position RH (fifth speed position), and low speed limit position RL (third speed position) in the automatic shifting range R of the load mode (or run mode), and the automatic shifting range R of the load mode (or run mode) remain as they are, the indicating element  64   d  of the speed indicator  64  corresponding to the fourth speed position blinks, and the other indicating elements  64   a - 64   c  and  64   e - 64   h  of the speed indicator  64  are off. Further, when the down-shift button  62  is pushed and the first and second main speed change devices  10  and  11  are operated to the third speed position, as shown in  FIG. 16(C) , the indicating element  64   c  of the speed indicator  64  corresponding to the third speed position blinks, and the other indicating elements  64   a,    64   b  and  64   d - 64   h  of the speed indicator  64  are off. 
   When, as shown in  FIG. 16(C) , the shift position of the first and second main speed change devices  10  and  11  is the low speed limit position RL (third speed position) of the automatic shifting range R of the load mode (or run mode), and when the down-shift button  62  is pushed and the first and second main speed change devices  10  and  11  are operated to the second speed position, as shown in  FIG. 16(D) , the second speed position of the first and second main speed change devices  10  and  11  is set as the low speed limit position RL of the automatic shifting range R of the load mode (or run mode), and the fourth speed position of the first and second main speed change devices  10  and  11  is set as the high speed limit position RH of the automatic shifting range R of the load mode (or run mode). The indicating elements  64   d,    64   c  and  64   b  of the speed indicator  64  corresponding to the fourth, third and second speed position are surrounded by the different color as the automatic shifting range R of the load mode (or run mode). The indicating element  64   b  of the speed indicator  64  corresponding to the second speed position blinks, and the other indicating elements  64   a,    64   c - 64   h  of the speed indicator  64  are off. 
   When, as shown in  FIG. 16(A) , the shift position of the first and second main speed change devices  10  and  11  is the high speed limit position RH (fifth speed position) of the automatic shifting range R of the load mode (or run mode), and when the up-shift button  62  is pushed and the first and second main speed change devices  10  and  11  are operated to the sixth speed position, as shown in  FIG. 16  (E), the sixth speed position of the first and second main speed change devices  10  and  11  is set as the high speed limit position RH of the automatic shifting range R of the load mode (or run mode), and the fourth speed position of the first and second main speed change devices  10  and  11  is set as the low speed limit position RL of the automatic shifting range R of the load mode (or run mode). The indicating elements  64   f,    64   e  and  64   d  of the speed indicator  64  corresponding to the sixth, fifth and fourth speed position are surrounded by the different color as the automatic shifting range R of the load mode (or run mode). The indicating element  64 f of the speed indicator  64  corresponding to the sixth speed position blinks, and the other indicating elements  64   a - 64   e,    64   g  and  64   h  of the speed indicator  64  are off.

Technology Classification (CPC): 8