Patent Publication Number: US-2007123386-A1

Title: Traveling System Auxiliary Speed Change Device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a traveling system auxiliary speed change device applied to a working vehicle such as a tractor.  
      2. Background Art  
      In a working vehicle in which a synchronous multi-stage speed change device is interposed in a traveling system transmission path from an engine to driving wheels, it is conventionally known to interpose a traveling system auxiliary speed change device including a forward-reverse switching mechanism and a high-low speed switching mechanism between the engine and the synchronous multi-stage speed change device (see e.g., Japanese Laid-Open Patent Publication No. 2002-79839).  
      By interposing the forward-reverse switching mechanism and the high-low speed switching mechanism between the engine and the synchronous multi-stage speed change device, the transmitting direction of the traveling system transmission path can be switched and the speed change range of the traveling system transmission path can be enlarged.  
      The synchronous multi-stage speed change device is configured to change the rotation speed on the driven side with respect to the rotation speed on the driving side by engaging the corresponding driving-side spline and the driven-side spline after synchronously rotating a synchronizer ring and a synchronizing cone through friction engagement, where the speed change operation of the synchronous multi-stage speed change device is performed on the basis that the traveling system transmission path is in a power-disconnected state.  
      Specifically, the forward-reverse switching mechanism is configured so as to be brought into the power-disconnected state in conjunction with the disconnecting operation of a clutch operation member arranged in the vicinity of the driver&#39;s seat of the working vehicle. The synchronous multi-stage speed change device is operated so as to change speed after the forward-reverse switching mechanism is brought into the power-disconnected state by the clutch operation member.  
      However, sufficient consideration is not made in reducing the volume of the synchronous multi-stage speed change device in the conventional working vehicle of the type equipped with the traveling system auxiliary speed change device and the synchronous multi-stage speed change device.  
      That is, in the conventional working vehicle, the forward-reverse switching mechanism is arranged on the upstream side in the power-transmitting direction from the high-low speed switching mechanism.  
      In the conventional configuration, the driving side of the synchronous multi-stage speed change device remains operatively connected to the high-low speed switching mechanism even if the forward-reverse switching mechanism is shifted to the power-disconnected state by the clutch operation member in order to operate the synchronous multi-stage speed change device for changing speed.  
      Therefore, the synchronizer ring and the synchronizing cone must absorb the inertia energy of the high-low speed switching mechanism when synchronizing the synchronizer ring and the synchronizing cone in time of the speed change operation of the synchronous multi-stage speed change device.  
      In other words, the device having a synchronizing capacity capable of absorbing the inertia energy of the high-low speed switching mechanism must be used for the synchronous multi-stage speed change device in the conventional working vehicle, resulting in enlarging the synchronous multi-stage speed change device.  
     SUMMARY OF THE INVENTION  
      The present invention, in view of the above, aims to provide a traveling system auxiliary speed change device including a high-low speed switching mechanism and a forward-reverse switching mechanism interposed between the engine and the synchronous multi-stage speed change device, the traveling system auxiliary speed change device capable of achieving miniaturization of the synchronous multi-stage speed change device, while having a simple configuration.  
      According to the present invention, there is provided a traveling system auxiliary speed change device interposed between an engine and a synchronous multi-stage speed change device, the traveling system auxiliary speed change device including a high-low speed switching mechanism and a forward-reverse switching mechanism arranged in order from an upstream side to a downstream side in a power-transmitting direction. The forward-reverse switching mechanism is configured to be brought into a power-disconnected state in conjunction with a disconnecting operation of a clutch operation member for engaging or releasing the transmission state of a traveling system transmission path from the engine to driving wheels.  
      With the traveling system auxiliary speed change device according to the present invention, the driving side of the synchronous multi-stage speed change device is brought into the disconnected state with respect to the high-low speed switching mechanism in a time of the speed change operation of the synchronous multi-stage speed change device arranged on the downstream side in the power-transmitting direction from the traveling system auxiliary speed change device.  
      Specifically, according to the present invention, the inertia energy of the high-low speed switching mechanism does not act on the driving side of the synchronous multi-stage speed change device in time of the speed change operation of the synchronous multi-stage speed change device. Therefore, the device having a small synchronizing capacity may be used as the synchronous multi-stage speed change device, thereby enhancement in operation feeling, reduction in cost, and miniaturization could be achieved.  
      In a case where the forward-reverse switching mechanism is configured so as to switch the power-transmitting direction from its driving side operatively connected to the high-low speed switching mechanism to its driven side operatively connected to the synchronous multi-stage speed change device by a multi-plate clutch unit, the multi-plate clutch unit is preferably positioned on the drive side of the forward-reverse switching mechanism.  
      With the configuration, in time of the speed change operation of the synchronous multi-stage speed change device, the inertia energy of a clutch housing and a piston in the multi-plate type clutch unit is prevented from acting on the driving side of the synchronous multi-stage speed change device, whereby the synchronous multi-stage speed change device could be further miniaturized.  
      Preferably, the traveling system auxiliary speed change device further has a housing including a housing main body, and a bearing member removably connected at an intermediate portion in a fore-and-aft direction of the housing main body so as to divide an inner space of the housing main body into a front chamber and a rear chamber. The high-low speed switching mechanism and the forward-reverse switching mechanism are respectively accommodated within the front chamber and the rear chamber.  
      With the configuration, the assembly of both switching mechanisms could be enhanced, and the strength of a housing member for both switching mechanisms could be enhanced.  
      In a case where each of the high-low speed switching mechanism and the forward-reverse switching mechanism is configured so as to transmit the power from its driving side to its driven side by a multi-plate clutch unit, the high-low speed switching clutch unit of the high-low speed switching mechanism and the forward-reverse switching clutch unit of the forward-reverse switching mechanism are preferably positioned on different axial lines.  
      With the configuration, the respective hydraulic fluid supply configurations for the clutch units are arranged on the bearing member while thinning the thickness of the bearing member.  
      In one embodiment, the high-low speed switching mechanism includes a high-low speed switching drive shaft operatively connected to the engine, and a high-low speed switching driven shaft arranged substantially parallel to the high-low speed switching drive shaft in a state of being operatively connected to the high-low speed switching drive shaft through the high-low speed switching clutch unit. The forward-reverse switching mechanism includes a forward-reverse switching drive shaft positioned coaxially with the high-low speed switching driven shaft in a state of being relatively non-rotatable to the high-low speed switching driven shaft about its axial line, and a forward-reverse switching driven shaft arranged so as to be operatively connected to the forward-reverse switching drive shaft through the forward-reverse switching clutch unit. The high-low speed switching clutch unit and the forward-reverse switching clutch unit are positioned on the corresponding drive shafts.  
      Preferably, the high-low speed switching drive shaft is positioned above the high-low speed switching driven shaft.  
      With the configuration, the viscosity resistance by the stored fluid on the forward-reverse switching clutch unit could be reduced even if fluid is stored in the internal space of the housing main body. Therefore, the forward-reverse switching clutch unit could be brought into a half-clutch state with satisfactory accuracy.  
      In another embodiment, the high-low speed switching mechanism includes a high-low speed switching drive shaft operatively connected to the engine, and a high-low speed switching driven shaft arranged substantially parallel to the high-low speed switching drive shaft in a state of being operatively connected to the high-low speed switching drive shaft through the high-low speed switching clutch unit. The forward-reverse switching mechanism includes a forward-reverse switching drive shaft positioned coaxially with the high-low speed switching driven shaft in a state of being relatively non-rotatable to the high-low speed switching driven shaft about its axial line, and a forward-reverse switching driven shaft arranged coaxially with high-low speed switching drive shaft in a state of being operatively connected to the forward-reverse switching drive shaft through the forward-reverse switching clutch unit. The high-low speed switching clutch unit and the forward-reverse switching clutch unit are positioned on the corresponding driven shafts.  
      Preferably, the high-low speed switching driven shaft is positioned below the high-low speed switching drive shaft.  
      With the configuration, the viscosity resistance by the stored fluid on the forward-reverse switching clutch unit could be reduced even if fluid is stored in the internal space of the housing main body. Therefore, the forward-reverse switching clutch unit could be brought into a half-clutch state with satisfactory accuracy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings.  
       FIG. 1  is a schematic view illustrating a power-transmitting path of a working vehicle to which a traveling system auxiliary speed change device according to an embodiment 1 of the present invention is applied.  
       FIG. 2  is a vertical cross-sectional side view of the vicinity of the traveling system auxiliary speed change device according to the embodiment 1.  
       FIG. 3  is a schematic view illustrating a power-transmitting path of a working vehicle to which a traveling system auxiliary speed change device according to a modified embodiment is applied.  
       FIG. 4  is a vertical cross-sectional side view of the vicinity of the traveling system auxiliary speed change device according to another modified embodiment.  
       FIG. 5  is a hydraulic circuit diagram of the working vehicle shown in  FIG. 1 .  
       FIG. 6  is a hydraulic circuit diagram of a forward-reverse switching hydraulic circuit forming a part of the hydraulic circuit in the working vehicle.  
       FIG. 7  is a vertical cross-sectional side view of the vicinity of a traveling system auxiliary speed change device according to an embodiment 2 of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Embodiment 1  
      One preferred embodiment of a traveling system auxiliary speed change device according to the present invention will now be described with reference to the accompanied drawings.  
       FIG. 1  is a schematic view illustrating a power-transmitting path of a working vehicle  100  to which a traveling system auxiliary speed change device  1 A according to the present embodiment is applied.  
       FIG. 2  is a vertical cross-sectional side view of the vicinity of the traveling system auxiliary speed change device  1 A.  
      As shown in  FIG. 1 , the traveling system auxiliary speed change device  1 A is interposed in the traveling system transmission path from an engine  110  (see  FIG. 5 ) to driving wheels.  
      Specifically, in the present embodiment, the working vehicle  100  includes a traveling system transmission structure forming the traveling system transmission path.  
      As shown in  FIG. 1 , the traveling system transmission structure includes a driving force shaft  130  operatively connected to the engine  110  by way of a flywheel  120 ; a synchronous multi-stage speed change device  200  serving as a main speed change device; a complex multi-stage speed change device  250  serving as a sub-speed change device; a main differential gear device  150  for differentially transmitting the output from the sub-speed change device to a pair of left and right main driving axles  140 ; and the traveling system auxiliary speed change device  1 A interposed between the engine  110  and the synchronous multi-stage speed change device  200 .  
      The reference character  300  in  FIG. 1  is a sub-driving wheel driving unit removably arranged in the traveling system transmission structure. The sub-driving wheel driving unit  300  is configured so as to output the driving force synchronized with the driving force, which is input to the main differential gear device  150 , towards the sub-driving wheels.  
      In the present embodiment, the working vehicle  100  also includes a PTO system transmission structure for outputting the power from the engine  110  towards the outside, in addition to the traveling system transmission structure.  
      The PTO system transmission structure includes a PTO transmission shaft  410  coupled to the driving force shaft  130  in a relatively non-rotatable manner about the axis line, a PTO clutch device  420  having a driving side operatively connected to the PTO transmission shaft  410 , and a PTO shaft  450  operatively connected to a driven side of the PTO clutch device  420 .  
      The traveling system auxiliary speed change device  1 A, which is arranged between the engine  110  and the synchronous multi-stage speed change device  200  as described above, switches the transmitting direction and enlarges the speed changing range in each transmitting direction.  
      Specifically, the traveling system auxiliary speed change device  1 A includes a high-low speed switching mechanism  10  and a forward-reverse switching mechanism  50 .  
      The high-low speed switching mechanism  10  is configured so as to switch the power-transmitting speed from its driving side to its driven side according to the operation of a high-low speed switching operation member such as H/L switching lever and the like, arranged in a vicinity of a driver&#39;s seat of the working vehicle  100 .  
      The forward-reverse switching mechanism  50  is configured so as to switch the power-transmitting direction from its driving side to its driven side into a forward direction or a reverse direction according to the operation of a forward-reverse switching operation member such as a forward-reverse switching lever arranged in the vicinity of the driver&#39;s seat, and to have the power-transmission from the driving side to the driven side in the disconnected state according to the disconnecting operation of a clutch operation member such as a clutch pedal.  
      The forward-reverse switching operation member and the clutch operation member may be separate to each other, but may obviously be integrally formed as a single member.  
      In the traveling system auxiliary speed change device  1 A having the above configuration, the high-low speed switching mechanism  10  is positioned on the upstream side in the power-transmitting direction from the forward-reverse switching mechanism  50 , whereby the volume of the synchronous multi-stage speed change device  200  could be reduced.  
      In other words, the synchronous multi-stage speed change device  200  is configured to engage the corresponding driving-side spline and the driven-side spline after synchronously rotating the synchronizer ring and the synchronizing cone through friction engagement in a time of the speed change operation from the driving side to the driven side.  
      The driven side of the synchronous multi-stage speed change device  200  is operatively connected to the main driving wheel by way of various transmission members. Therefore, in the speed change operation of the synchronous multi-stage speed change device  200 , the synchronizer ring and the synchronizing cone have to synchronize the rotation speed of the driving side to the rotation speed of the driven side while being against the inertia energy of the driving side.  
      Therefore, the speed change operation of the synchronous multi-stage speed change device  200  is performed on the basis that the forward-reverse switching mechanism  50  is in the power disconnected state by the clutch operation member, whereas in the conventional traveling system auxiliary speed change device, a great inertia energy acts on the driving side of the synchronous multi-stage speed change device in the speed change operation of the synchronous multi-stage speed change device since the forward-reverse switching mechanism is arranged on the upstream side in the transmitting direction from the high-low speed switching mechanism, resulting in arising a problem of enlarging the synchronous multi-stage speed change device.  
      More specifically, in the conventional configuration in which the forward-reverse switching mechanism, the high-low speed switching mechanism, and the synchronous multi-stage speed change device are arranged in order from the upstream side to the downstream side in the transmitting direction, the high-low speed switching mechanism remains operatively connected on the driving side of the synchronous multi-stage speed change device even if the forward-reverse switching mechanism is shifted to the power-disconnected state in time of the speed change operation of the synchronous multi-stage speed change device.  
      Therefore, the synchronizer ring and the synchronizing cone are required to synchronize the driving side with the driven side while being against the inertia energy of the high-low speed switching mechanism in time of the speed change operation of the synchronous multi-stage speed change device, and the device having a synchronizing volume capable of absorbing the inertia energy of the high-low speed switching mechanism has to be used as the synchronous multi-stage speed change device.  
      In the traveling system auxiliary speed change device  1 A according to the present embodiment, on the other hand, the high-low speed switching mechanism  10  is positioned on the upstream side in the transmitting direction from the forward-reverse switching mechanism  50 , as described above. In other words, the high-low speed switching mechanism  10 , the forward-reverse switching mechanism  50  and the synchronous multi-stage speed change device  200  are arranged in order from the upstream side to the downstream side in the transmitting direction.  
      According to the above configuration, the inertia energy of the high-low speed switching mechanism  10  does not act on the driving side of the synchronous multi-stage speed change device  200  when the forward-reverse switching mechanism  50  is in the power-disconnected state in time of the speed change operation of the synchronous multi-stage speed change device  200 .  
      Therefore, a small device having a small synchronizing capacity could be used as the synchronous multi-stage speed change device  200 , whereby enhancement in the operation feeling, reduction in cost and miniaturization of the synchronous multi-stage speed change device  200  are achieved.  
      In the present embodiment, the complex multi-stage speed change device  250  includes a synchronous multi-stage speed change mechanism and a gear-sliding multi-stage speed change mechanism, as shown in  FIG. 1 .  
      Therefore, the synchronous multi-stage speed change mechanism in the complex multi-stage speed change mechanism  250  can be miniaturized by positioning the high-low speed switching mechanism  10  on the upstream side in the transmitting direction from the forward-reverse switching mechanism  50 .  
      The detailed configuration of the traveling system auxiliary speed change device  1 A will now be described.  
      In the present embodiment, the forward-reverse switching mechanism  50  includes a multi-plate clutch unit  60 , and is configured so as to switch the power-transmitting direction from the driving side to the driven side and to disconnect the power-transmission from the driving side to the driven side by the multi-plate clutch unit  60 , as shown in  FIGS. 1 and 2 .  
      Specifically, the forward-reverse switching clutch unit  60  includes a clutch housing  61  supported in a relatively non-rotatable manner at a corresponding supporting shaft (hereinafter referred to as forward-reverse switching clutch supporting shaft); a forward gear member  62 F and a reverse gear member  62 R supported in a relatively rotatable manner at the forward-reverse switching clutch supporting shaft so as to be respectively positioned on one side (upstream side in the transmitting direction) and the other side (downstream side in the transmitting direction) in the axis line direction of the forward-reverse switching clutch supporting shaft with a partition wall of the clutch housing  61  in between; a forward friction plate group  63 F including a forward gear member-side friction plate supported at the forward gear member  62 F in a relatively non-rotatable manner and in a relatively movable manner in the axis line direction and a forward clutch housing-side friction plate supported at the clutch housing  61  in a relatively non-rotatable manner and in a relatively movable manner in the axis line direction so as to face the forward gear member-side friction plate; a forward piston  64 F for frictionally engaging the forward friction plate group  63 F; a reverse friction plate group  63 R including a reverse gear member-side friction plate supported at the reverse gear member  62 R in a relatively non-rotatable manner and in a relatively movable manner in the axis line direction and a reverse clutch housing-side friction plate supported at the clutch housing  61  in a relatively non-rotatable manner and in a relatively movable manner in the axis line direction so as to face the reverse gear member-side friction plate; and a reverse piston  64 R for frictionally engaging the reverse friction plate group  63 R.  
      In the present embodiment, the forward-reverse clutch unit  60  is of a hydraulic operation type in which the forward piston  64 F and the reverse piston  64 R frictionally engage the corresponding forward friction plate group  63 F and the reverse friction plate group  63 R through the action of the hydraulic pressure, respectively.  
      Therefore, in addition to the above configuration, the forward-reverse switching clutch unit  60  includes a forward biasing member  65 F for biasing the forward piston  64 F in a direction away from the forward friction plate group  63 F, and a reverse biasing member  65 R for biasing the reverse piston  64 R in a direction away from the reverse friction plate group  63 R.  
      In the present embodiment, the forward-reverse switching clutch unit  60  is arranged on the driving side in the forward-reverse switching mechanism  50 , as shown in  FIGS. 1 and 2 , whereby the inertia energy that acts on the driving side of the synchronous multi-stage speed change device  200  in time of the speed change operation of the synchronous multi-stage speed change device  200  is further reduced.  
      Specifically, the forward-reverse switching mechanism  50  includes a forward-reverse switching drive shaft  51  operatively connected to the high-low speed switching mechanism  10  arranged on the upstream side in the transmitting direction from the forward-reverse switching mechanism  50 , and a forward-reverse switching driven shaft  55  operatively connected to the synchronous multi-stage speed change device  200  arranged on the downstream side in the transmitting direction from the forward-reverse switching mechanism  50  in the present embodiment, where the forward-reverse switching drive shaft  51  acts as the forward-reverse switching clutch supporting shaft.  
      By arranging the forward-reverse switching clutch unit  60  on the driving side in the forward-reverse switching mechanism  50 , as described above, the clutch housing  61  as well as the forward piston  64 F and the reverse piston  64 R are disconnected to the synchronous multi-stage speed change device  200  when the forward-reverse switching mechanism  50  is shifted to the power-disconnected state in time of the speed change operation of the synchronous multi-stage speed change device  200 .  
      Therefore, the inertia energy that acts on the driving side of the synchronous multi-stage speed change device  200  in time of the speed change operation of the synchronous multi-stage speed change device  200  is further reduced.  
      In the present embodiment, the forward-reverse switching mechanism  50  is of a two parallel shafts type in which the forward-reverse switching drive shaft  51  is coaxially coupled to a high-low speed switching driven shaft  15  in the high-low speed switching mechanism  10  in a relatively non-rotatable manner about the axis line, and the forward-reverse switching driven shaft  55  is arranged substantially parallel to the forward-reverse switching drive shaft  51 , as shown in  FIGS. 1 and 2 , but the present invention is obviously not limited to the configuration.  
      For example, the forward-reverse switching mechanism  50  may be configured to include the forward-reverse switching drive shaft  51 , the forward-reverse switching driven shaft  55  arranged coaxially with the forward-reverse switching drive shaft  51  in a state of being relatively rotatable about the axis line, and a reverse transmission shaft  53  arranged substantially parallel to the forward-reverse switching drive shaft  51 , as shown in  FIG. 3 .  
      In the forward-reverse switching mechanism  50  shown in  FIG. 3 , the reverse gear member  62 R is supported at the forward-reverse switching drive shaft  51  at one side in the axis line direction (upstream side in the transmitting direction) of the clutch housing  61 . The forward gear member  62 F is positioned on the other side in the axis line direction (downstream side in the transmitting direction) of the clutch housing  61  in a state of being rotatable with respect to the forward-reverse switching drive shaft  51  and relatively non-rotatable with respect to the forward-reverse switching driven shaft  55 .  
      The high-low speed switching mechanism  10  includes a multi-plate clutch unit  20 , and is configured so as to switch the rotation speed of the power transmitted from the driving side to the driven side through the multi-plate clutch unit  20 , as shown in  FIGS. 1 and 2 .  
      Specifically, the high-low speed switching mechanism  10  includes a high-low speed switching drive shaft  11  operatively connected to the driving force shaft  130 , a high-low speed switching driven shaft  15  arranged substantially parallel to the high-low speed switching drive shaft  11 , and the high-low speed switching clutch unit  20 . The high-low speed switching mechanism  10  is configured to rotate the high-low speed switching driven shaft  15  at the rotation speed corresponding to the high speed stage or the low speed state through the clutch unit  20 .  
      In the present embodiment, the high-low speed switching drive shaft  11  is integrally formed with the driving force shaft  130  (see  FIG. 2 ).  
      The high-low speed switching clutch unit  20  is supported at one of the shafts (hereinafter referred to as high-low speed switching clutch supporting shaft) of the high-low speed switching drive shaft  11  or the high-low speed switching driven shaft  15 .  
      In the present embodiment, the high-low speed switching drive shaft  11  serves as the high-low speed switching clutch supporting shaft, as shown in  FIGS. 1 and 2 .  
      Specifically, the high-low speed switching clutch unit  20  includes a clutch housing  21  supported at the high-low speed switching clutch supporting shaft in a relatively non-rotatable manner; a high speed stage gear member  22 H and a low speed stage gear member  22 L supported at the high-low speed switching clutch supporting shaft in a relatively rotatable manner so as to be respectively positioned at one side and the other side in the axis line direction with the clutch housing  21  in between; a high speed stage friction plate group  23 H including a high speed stage gear member-side friction plate supported at the high speed stage gear member  22 H in a relatively non-rotatable manner and in a movable manner in the axis line direction and a high speed stage clutch housing-side friction plate supported at the clutch housing  21  in a relatively non-rotatable manner and in a movable manner in the axis line direction so as to face the high speed stage gear member-side friction plate; a high speed stage piston  24 H for frictionally engaging the high speed stage friction plate group  23 H; a low speed stage friction plate group  23 L including a low speed stage gear member-side friction plate supported at the low speed stage gear member  22 L in a relatively non-rotatable manner and in a movable manner in the axis line direction and a low speed stage clutch housing-side friction plate supported at the clutch housing  21  in a relatively non-rotatable manner and in a movable manner in the axis line direction so as to face the low speed stage gear member-side friction plate; and a low speed stage piston  24 L for frictionally engaging the low speed stage friction plate group  23 L.  
      In the present embodiment, the high-low speed switching clutch unit  20  is of a hydraulic operation type in which both of the high speed stage piston  24 H and the low speed stage piston  24 L frictionally engage the corresponding friction plate group  23 H,  23 L through the action of the hydraulic pressure.  
      Therefore, the high-low speed switching clutch unit  20  further includes a high speed stage biasing member  25 H for biasing the high speed stage piston  24 H in the direction away from the high speed stage friction plate group  23 H, and a low speed stage biasing member  25 L for biasing the low speed stage piston  24 L in the direction away from the low speed stage friction plate group  23 L.  
      In the present embodiment, the high-low speed switching clutch unit  20  is of a hydraulic operation type in which the pistons  24 H,  24 L frictionally engage the corresponding friction plate groups  23 H,  23 L through the action of the hydraulic pressure, as described above, but in place thereof, the high-low speed switching clutch unit  20  may be of a spring operating type in which both pistons  24 H,  24 L frictionally engage the corresponding friction plate group  23 H,  23 L through the action of the spring, or a complex type in which one of the pistons  24 H,  24 L frictionally engages the corresponding friction plate group  23 H,  23 L through the action of the hydraulic pressure and the other piston frictionally engages the corresponding friction plate group  23 H,  23 L through the action of the spring.  
      The high-low speed switching clutch unit  20  and the forward-reverse switching clutch unit  60  are preferably displaced to each other in respect to the axis position or arranged in a decentered manner as in the present embodiment (see  FIGS. 1 and 2 ) and the modified embodiment (see  FIG. 3 ).  
      That is, the high-low speed switching clutch supporting shaft and the forward-reverse switching clutch supporting shaft are configured so as not to be coaxially positioned to each other.  
      By arranging the high-low speed switching clutch unit  20  and the forward-reverse switching clutch unit  60  in a decentered manner as described above, the width in the fore-and-aft direction of a bearing member  520 , which supports the downstream ends in the transmitting direction of the high-low speed switching drive shaft  11  and the driven shaft  15  and the upstream end in the transmitting direction of the forward-reverse switching drive shaft  51 , can be made thin even if both a rotary joint forming a hydraulic fluid supply structure for the high-low speed switching clutch unit  20  and a rotary joint forming a hydraulic fluid supply structure for the forward-reverse switching clutch unit  60  are formed at the bearing member  520 .  
      A structure for supporting the high-low speed switching mechanism  10  and the forward-reverse switching mechanism  50  will now be described.  
      As shown in  FIGS. 1 and 2 , the high-low speed switching mechanism  10  and the forward-reverse switching mechanism  50  are accommodated in a single housing  500  in the present embodiment.  
      In the present embodiment, the housing  500  is connected on the front side in the fore-and-aft direction of an intermediate housing  550  for accommodating the main speed change device  200  and the sub-speed change device  250 , and is configured to form a part of a vehicle frame of the working vehicle  100 .  
      Specifically, the working vehicle  100  includes the intermediate housing  550 , and a rear housing  560  that accommodates the main differential gear device  150  and is connected on the rear side in the fore-and-aft direction of the intermediate housing  550 .  
      The housing  500 , the intermediate housing  550 , and the rear housing  560  are connected in series along the fore-and-aft direction of the vehicle to form the vehicle frame.  
      The housing  500  includes a housing main body  510  and the bearing member  520 .  
      In the present embodiment, the housing main body  510  is configured to accommodate the high-low speed switching mechanism  10  and the forward-reverse switching mechanism  50  and also to accommodate the flywheel  120  positioned on the upstream side in the power-transmitting direction of the high-low switching mechanism  10 .  
      Specifically, the housing main body  510  includes a hollow peripheral wall  511  extending in the fore-and-aft direction of the vehicle, and a partition wall  512  integrally formed with the peripheral wall  511  so as to divide the internal space defined by the peripheral wall  511  into the front side and the rear side in the fore-and-aft direction of the vehicle.  
      The flywheel  120  is accommodated in a dry chamber positioned on the front side in the fore-and-aft direction with the partition wall  512  as the reference, and the high-low speed switching mechanism  10  and the forward-reverse switching mechanism  50  are accommodated in an oil chamber positioned on the rear side in the fore-and-aft direction with the partition wall  512  as the reference.  
      The bearing member  520  is removably connected at the intermediate portion in the fore-and-aft direction of the peripheral wall  511  in the housing main body  510  so as to divide the oil chamber into a front chamber and a rear chamber.  
      The high-low speed switching mechanism  10  is accommodated in the front chamber, and the forward-reverse switching mechanism  50  is accommodated in the rear chamber.  
      Specifically, the high-low speed switching drive shaft  11  and the high-low speed switching driven shaft  15  have the upstream ends in the power-transmitting direction supported at the partition wall  512  and the downstream ends in the power-transmitting direction supported at the bearing member  520 , as shown in  FIGS. 1 and 2 .  
      The forward-reverse switching drive shaft  51  and the forward-reverse driven shaft  55  have the upstream ends in the power-transmitting direction supported at the bearing member  520  and the downstream ends in the power-transmitting direction supported at a second bearing member  530 , which is removably connected to the rear end in the fore-and-aft direction of the housing main body  510 , as shown in  FIGS. 1 and 2 .  
      As described above, in the present embodiment, the high-low speed switching mechanism  10  and the forward-reverse switching mechanism  50  are accommodated in the single housing  500 , whereby the strength is enhanced compared to a configuration in which dedicated housings for accommodating the respective switching mechanism  10 ,  50  are connected.  
      Moreover, in the present embodiment, the high-low speed switching mechanism  10  and the forward-reverse switching mechanism  50  are supported by utilizing the bearing member  520  removable with respect to the housing main body  510 , whereby the assembly of the switching mechanisms  10 ,  50  is enhanced.  
      Furthermore, in the present embodiment, the high-low speed switching clutch unit  20  in the high-low speed switching mechanism  10  and the forward-reverse switching clutch unit  60  in the forward-reverse switching mechanism  50  are arranged in a decentered manner, as described above.  
      Therefore, even if both the rotary joint for the high-low speed switching clutch unit  20  and the rotary joint for the forward-reverse switching clutch unit  60  are formed at the bearing member  520 , which is positioned between the high-low speed switching mechanism  10  and the forward-reverse switching mechanism  50 , for supporting both switching mechanisms, as in the present embodiment, the rotary joints are arranged so as to be displaced to each other, and thus the width in the fore-and-aft direction of the bearing member  520  can be made as thin as possible.  
      In the present embodiment and the modified embodiment, the high-low speed switching clutch unit  20  and the forward-reverse switching clutch unit  60  are arranged in a decentered manner by having the high-low speed switching clutch unit  20  and the forward-reverse switching clutch unit  60  respectively supported at the corresponding drive shaft  11 ,  51  in a configuration in which the high-low speed switching drive shaft  11  and the high-low speed switching driven shaft  15  are arranged substantially parallel and the forward-reverse switching drive shaft  51  and the high-low speed switching driven shaft  15  are concentrically arranged, as shown in FIGS.  1  to  3 , but the present invention is obviously not limited thereto.  
      In other words, as shown in  FIG. 4 , the high-low speed switching clutch unit  20  and the forward-reverse switching clutch unit  60  may be arranged in a decentered manner by having the high-low speed switching clutch unit  20  and the forward-reverse switching clutch unit  60  supported at the corresponding driven shafts  15 ,  55  in a configuration in which the high-low speed switching drive shaft  11  and the high-low speed switching driven shaft  15  are arranged substantially parallel, the forward-reverse switching drive shaft  51  is arranged concentrically with the high-low speed switching driven shaft  15 , and the forward-reverse switching driven shaft  55  is arranged substantially parallel to the forward-reverse switching drive shaft  51  so that the forward-reverse switching driven shaft  55  is positioned concentrically with the high-low speed switching drive shaft  11 .  
      In the modified embodiment shown in  FIG. 4 , the high-low speed switching drive shaft  11  is positioned above the high-low speed switching driven shaft  15 , and thus the forward-reverse switching driven shaft  55  positioned coaxially with the high-low speed switching drive shaft  11  and supporting the forward-reverse switching clutch unit  60  is arranged above the forward-reverse switching drive shaft  51 .  
      In the configuration, the influence of the fluid stored in the fluid chamber on the forward-reverse switching clutch unit  60  is reduced, and the accuracy of a half-clutch control of the forward-reverse switching clutch unit  60  is enhanced.  
      In other words, the forward-reverse switching mechanism  50  is configured so as to selectively take a forward transmission state, a reverse transmission state or a power-shutoff state with respect to the power-transmission from the forward-reverse switching drive shaft  51  to the forward-reverse driven shaft  55 . Specifically, the forward-reverse switching mechanism  50  further takes a half-clutch state in which the power is partially transmitted from the forward-reverse switching drive shaft  51  to the forward-reverse switching driven shaft  55 , in addition to the forward transmission state, the reverse transmission state and the power-shutoff state.  
      The half-clutch state is obtained by bringing the forward friction plate group  63 F (or reverse friction plate group  63 R) into a frictional engagement state with the forward gear member-side friction plate and the forward clutch housing-side friction plate being slid to each other, whereby sudden speed change of the working vehicle  100  is prevented when starting the working vehicle  100  from the stopped state or when stopping the working vehicle from the traveling state.  
      Specifically, the oil chamber for accommodating the forward-reverse switching mechanism  50  is configured to have the internal space capable of storing oil, as well as the intermediate housing  550  and the rear housing  560 .  
      Therefore, if the forward-reverse switching clutch unit  60  is arranged at the lower portion in the oil chamber, the stored fluid is interposed between the corresponding friction plates in the forward friction plate group  63 F (or reverse friction plate group  63 R), and it is difficult to bring the forward-reverse switching clutch unit  60  into the half-clutch state due to the viscosity resistance of the stored oil.  
      With regards to this point, the forward-reverse switching clutch unit  60  is supported at the forward-reverse switching driven shaft  55  arranged above the forward-reverse switching drive shaft  51 , as described above, in the modified embodiment shown in  FIG. 4 .  
      Accordingly, the adverse affect of the stored fluid in the fluid chamber on the forward-reverse switching clutch unit  60  is prevented as much as possible.  
      The enhancement in the accuracy control of the half-clutch state is obviously not limited to the modified embodiment shown in  FIG. 4 .  
      In other words, the adverse affect of the stored fluid on the forward-reverse switching clutch unit  60  is also prevented as much as possible by arranging the high-low speed switching drive shaft  11  under the high-low speed switching driven shaft  15 , and arranging the forward-reverse switching drive shaft  51  coaxially with the high-low speed switching driven shaft  15 , and further, by having the high-low speed switching clutch unit  20  and the forward-reverse switching clutch unit  60  supported at the corresponding drive shafts  11 ,  51 .  
      The hydraulic circuit in the working vehicle  100  will now be described.  
       FIG. 5  shows a hydraulic circuit diagram of the working vehicle  100 .  
      Furthermore,  FIG. 6  shows a hydraulic circuit diagram of a forward-reverse switching hydraulic circuit  650  forming a part of the hydraulic circuit in the working vehicle  100 .  
      As shown in  FIGS. 5 and 6 , the working vehicle  100  includes a fluid tank  610 ; a hydraulic pump  620  configured so as to employ the stored fluid in the fluid tank  610  as a fluid source; and a high-low speed switching mechanism hydraulic circuit  630  and a forward-reverse switching mechanism hydraulic circuit  650  to which the hydraulic fluid is supplied from the hydraulic pump  620 .  
      In the present embodiment, the working vehicle  100  further includes a power steering hydraulic circuit  670  and a PTO clutch hydraulic circuit  680  to which the hydraulic fluid is supplied from the hydraulic pump  620 .  
      As described above, the oil chamber in the housing  500  as well as the internal spaces of the intermediate housing  550  and the rear housing  560  are capable of storing fluid, and such internal spaces are also commonly used as the fluid tank  610 , in the present embodiment.  
      The hydraulic pump  620  is operatively driven by the engine  110 .  
      In the present embodiment, the hydraulic pump  620  includes first and second hydraulic pumps  621 ,  622 .  
      The first hydraulic pump  621  is configured to supply the hydraulic fluid to the power steering hydraulic circuit  670 .  
      The second hydraulic pump  622  is configured to supply the hydraulic fluid to the high-low speed switching mechanism hydraulic circuit  630 , the forward-reverse switching hydraulic circuit  650 , and the PTO clutch hydraulic circuit  680 .  
      In the present embodiment shown in  FIGS. 1 and 2 , as well as the modified embodiments shown in  FIGS. 3 and 4 , the second hydraulic pump  622  is supported at the front surface of the partition wall  512 , and the first hydraulic pump  621  is arranged on the engine side.  
      The forward-reverse switching mechanism hydraulic circuit  650  includes a forward-reverse switching hydraulic fluid line  651  and a forward-reverse switching lubricating fluid line  661 , as shown in  FIG. 6 .  
      The forward-reverse switching hydraulic fluid line  651  is configured to supply the pressure fluid from the second hydraulic pump  622  to the forward-reverse switching clutch unit  60 .  
      Specifically, a hydraulic fluid pressure setting relief valve  652  for setting the hydraulic pressure of the hydraulic fluid line  651 ; an inching valve  653  for communicating/shutting off the hydraulic fluid line  651  according to the operated amount of the clutch operation member; and a forward clutch ON/OFF valve  654 F and a reverse clutch ON/OFF valve  654 R for turning ON/OFF the supply of hydraulic fluid to the forward piston  64 F and the reverse piston  64 R, respectively, in conjunction with the operation of the forward-reverse switching operation member are interposed in the forward-reverse switching hydraulic fluid line  651 .  
      In the present embodiment, a pressure sensor  655  for detecting the hydraulic pressure of the hydraulic fluid line  651  is also interposed in the forward-reverse switching hydraulic fluid line  651 .  
      The forward-reverse switching lubricating fluid line  661  is configured to supply the relief fluid from the hydraulic fluid pressure setting relief valve  652  to the forward friction plate group  63 F and the reverse friction plate group  63 R.  
      Specifically, the forward-reverse switching lubricating fluid line  661  extends between the secondary side of the hydraulic fluid pressure setting relief valve  652  and each friction plate group  63 F,  63 R.  
      A lubricating fluid pressure setting relief valve  662 ; a lubricating fluid ON/OFF valve  663  for communicating/shutting off the lubricating fluid line  651  with the hydraulic fluid to the forward piston  64 F and the reverse piston  64 R as the pilot pressure; and flow rate control valves  664  for adjusting the fluid amount supplied to the friction plate group  63 F,  63 R according to the pushed amount of the corresponding piston  64 F,  64 R are interposed in the lubricating fluid line  661 .  
      The high-low speed switching mechanism hydraulic circuit  630  includes a high-low speed switching hydraulic fluid line  631  and a high-low speed switching lubricating fluid line  641 , as shown in  FIG. 5 .  
      The high-low speed switching hydraulic fluid line  631  is configured to supply the hydraulic fluid, which hydraulic pressure is set by the hydraulic fluid pressure setting relief valve  652 , to the high-low speed switching clutch unit  20 .  
      Specifically, a high speed stage clutch ON/OFF valve  632 H and a low speed stage clutch ON/OFF valve  632 L for turning ON/OFF the supply of hydraulic fluid to the high speed stage piston  24 H and the low speed stage piston  24 L, respectively, in conjunction with the operation of the high-low speed switching operation member are arranged in the high-low speed switching hydraulic fluid line  631 .  
      The high-low speed switching lubricating fluid line  641  is configured so as to supply the returned fluid from the power steering hydraulic circuit  670  to the high-low speed switching clutch unit  20 .  
      Specifically, a lubricating fluid pressure setting relief valve  642 ; and flow rate control valves  643  for adjusting the lubricating fluid amount supplied to the friction plate groups  23 H,  23 L with the hydraulic fluid pressure to the high speed stage piston  24 H and the low speed stage piston  24 L as the pilot pressure are interposed in the high-low speed switching lubricating fluid line  641 .  
      The PTO clutch hydraulic circuit  680  includes a PTO hydraulic fluid line  681  and a PTO lubricating fluid line  691 , as shown in  FIG. 5 .  
      The PTO hydraulic fluid line  681  is configured to supply the hydraulic fluid from the high-low speed switching hydraulic fluid line  631  to the PTO clutch device  420 .  
      In the present embodiment, the PTO clutch device  420  is provided with a PTO clutch unit  430  for selectively engaging/cutting off the power-transmission from the driving side to the driven side; and a PTO brake unit  440  for applying braking force to the driven side when the PTO clutch unit  430  cuts off the power-transmission.  
      Therefore, the PTO hydraulic fluid line  681  is configured to selectively supply the hydraulic fluid to the PTO clutch unit  430  or the PTO brake unit  440 .  
      Specifically, a switching valve  682  for selectively switching the supply and discharge of the hydraulic fluid with respect to the PTO clutch unit  430  or the PTO brake unit  440 ; and a modulating valve  683  for gradually increasing the hydraulic pressure in time of supplying the hydraulic fluid to the PTO clutch unit  430  are interposed in the PTO hydraulic fluid line  681 .  
     Embodiment 2  
      Another embodiment of the traveling auxiliary speed change device according to the present invention will now be described with reference to the attached drawing.  
       FIG. 7  is a vertical cross-sectional side view of the vicinity of the traveling system auxiliary speed change device  2 A according to the present embodiment.  
      In the figure, the same reference characters are denoted for the same members as in the embodiment 1, and the detailed explanations thereof are omitted.  
      The traveling system auxiliary speed change devices  1 A to  1 C according to the embodiment 1 (see  FIGS. 1 and 2 ) and the modified embodiment (see  FIGS. 3 and 4 ) are configured so that the high-low speed switching clutch unit  20  and the forward-reverse switching clutch unit  60  are displaced to each other in respect to axis positions. On the other hand, the traveling system auxiliary speed change devices  2 A according to the present embodiment is configured so that the high-low speed switching clutch unit  20  and the forward-reverse switching clutch unit  60  are positioned coaxially to each other.  
      Similarly to the embodiment 1 and the modified embodiments, in the traveling system auxiliary speed change devices  2 A as well, enhancement in operation feeling, reduction in cost, and miniaturization could be achieved.  
      In a case where both the clutch units  20 ,  60  are positioned coaxially, the rotary joints for the clutch units  20 ,  60  are also positioned coaxially to each other, resulting in enlarging the width in the fore-and-aft direction of the bearing member  520 .  
      With regard to this point, the second hydraulic pump  622 , which is supported at the front surface of the partition wall  512  in the embodiment 1, is arranged on the engine side so that the partition wall  512  could be close to the flywheel  120  as much as possible, thereby obtaining spaces for arranging the high-low speed switching mechanism  10  and the forward-reverse switching mechanism  50  while preventing enlargement of the width in the fore-and-aft direction of the traveling system auxiliary speed change device  2 A.  
      In the present embodiment, both the clutch units  20 ,  60  are positioned coaxially to each other by having the clutch units  20 ,  60  supported at the corresponding drive shafts  11 ,  51 . Alternatively, both the clutch units  20 ,  60  could be supported at the corresponding driven shafts  15 ,  55  so that they are positioned coaxially to each other.  
      Although the high-low speed switching drive shaft  11  is positioned above the high-low speed switching driven shaft  15  in the each embodiment and modified embodiment, the high-low speed switching drive shaft  11  could be obviously positioned below the high-low speed switching driven shaft  15 .  
      This specification is by no means intended to restrict the present invention to the preferred embodiments or modified embodiments set forth therein. Various modifications to the traveling system auxiliary speed change device may be made by those skilled in the art without departing from the spirit and scope of the present invention as defined in the appended claims.