Abstract:
A working vehicle propelled by independently driven right and left running units comprising a body frame with an engine mounted thereon; a front wheel unit for supporting the body frame in cooperation with the right and left running units; a left HST for receiving torque input from the engine; a right HST for receiving torque input from the engine; a left reduction mechanism for decelerating and transmitting torque output from the left HST to the left running unit; a right reduction mechanism for decelerating and transmitting torque output from the right HST to the right running unit; a left base block supported by the body frame, this base block forming a housing base for the left HST and a housing base for the left reduction mechanism; a right base block attached to the body frame, this base block forming a housing base for the right HST and a housing base for the right reduction mechanism. The base blocks are formed as port blocks for the HSTs, and define hydraulic ports in the housing bases for the HSTs.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a working vehicle propelled by independently driven right and left running units. More particularly, the invention relates to a working vehicle in which torque from an engine is divided and transmitted to right and left HSTs, and variable speed outputs of the right and left HSTs are decelerated and transmitted by right and left reduction mechanisms to right and left running units. 
     2. Description of the Related Art 
     The above working vehicle is steerable by independently shifting the right and left HSTs to set driving speeds (running speeds) and driving directions (forward or backward drive) of the right and left running units (typically rear wheels) to be different from each other. In this type of power train system of the working vehicle, the HSTs and reduction cases containing reduction mechanisms may be connected to be integral with each other. Then, by simply connecting the HSTs to the body frame, for example, the reduction cases also are connected to the body frame through the HSTs. This dispenses with a special mounting structure for connecting the reduction cases to the body frame. 
     An integrating connection structure for HSTs and reduction cases containing reduction mechanisms as noted above is known from Japanese Unexamined Patent Publication 2000-71790. However, where this connection structure is used, the reduction cases need to be made unnecessarily large in order to house reduction mechanisms therein for connection to the HSTs. A large space is required to accommodate the reduction cases, which enlarges the vehicle body itself, such as increasing the width and so on. Particularly, the stronger connections between the reduction cases and the HSTs result in the larger reduction cases, and thus the vehicle body. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to provide a technique for simplifying and strengthening a connection structure between reduction mechanisms and HSTs, and for rigidly fixing this integrated connection structure to a body frame. 
     The above object is fulfilled, according to this invention, by a working vehicle as set forth at the outset hereof, comprising a body frame; a front wheel unit for supporting the body frame in cooperation with the right and left running units; an engine mounted on the body frame; a left HST for receiving torque input from the engine; a right HST for receiving torque input from the engine; a left reduction mechanism for decelerating and transmitting torque output from the left HST to the left running unit; a right reduction mechanism for decelerating and transmitting torque output from the right HST to the right running unit; a left base block supported by the body frame, the base block forming a housing base for the left HST and a housing base for the left reduction mechanism; and a right base block supported by the body frame, this base block forming a housing base for the right HST and a housing base for the right reduction mechanism. 
     In this construction, each HST and each reduction mechanism are connected through a common base block. The connecting surfaces of the base block also serve as housing bases for attaching respective housings thereto. Thus, the HST and the reduction mechanism, respectively, are smoothly fixed to the base block together with their own housings made small and exclusively therefor. As a result, a connection structure is created for the reduction mechanism and HST, having the base block therebetween as a core. 
     In a preferred embodiment of the invention, the base block is formed as a port block of the HST, and the housing base for the HST defines hydraulic ports. That is, with the base block acting as a port block for the HST, a simple structure and an easy assembling are advantageously developed. 
     In another preferred embodiment of the invention, the body frame extends longitudinally of the vehicle body, and has a pair of right and left first sub-frames in form of plates and a pair of right and left second sub-frames in form of plates, the first sub-frames having front ends connected to the front wheel unit, and rear ends connected to the base blocks, the second sub-frames being also connected to the base blocks. The first sub-frames and the second sub-frames are connected to each other through the base blocks to form the entire body frame. Since the base blocks form part of the body frame, corresponding dedicated parts of the body frame are dispensed with, particularly the parts supporting the reduction mechanisms and the HSTs. Simply connecting the first and second sub-frames to the port blocks will complete assembling of the body frame having the reduction mechanisms and HSTs already connected thereto. 
     In a further preferred embodiment of the invention, the left base block acts as a left leg fixing base for fixedly supporting a left leg of a ROPS, and the right base block acts as a right leg fixing base for fixedly supporting a right leg of the ROPS. With this structure, attachment of the ROPS may be carried out simultaneously with the connection of the base blocks and the body frame. 
     This invention also proposes that the HST is set such that an output rotation speed is lower than an input rotation speed for an entire shift range. This may be achieved, for example, by constructing the HST to include a pump and a motor, and such that, for the entire shift range, an oil delivery rate per rotation of the pump is lower than an oil drain rate per rotation of the motor. With this technique employed, the running units are driven with sufficient torque over the entire shift range of the HSTs even where the reduction mechanisms have a relatively small reduction ratio. 
     Other features and advantages of this invention will be apparent from the following description of the embodiments to be taken with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation of a riding lawn mower; 
         FIG. 2  is a plan view of the riding lawn mower; 
         FIG. 3  is a plan view of a body frame; 
         FIG. 4  is a side view of the body frame; 
         FIG. 5  is a rear view of a ROPS; 
         FIG. 6  is a rear view, partly in section, of a transmission device; 
         FIG. 7  is a schematic diagram of the transmission device; 
         FIG. 8  is a sectional view of an HST and a reduction case; 
         FIG. 9  is a side view showing a connection structure between first and second sub-frames and a base block as seen from outside the vehicle body; 
         FIG. 10  is a side view showing the connection structure between the first and second sub-frames and the base block as seen from inside the vehicle body; 
         FIG. 11  is a plan view showing the connection structure between the first and second sub-frames and the base blocks; and 
         FIG. 12  is a perspective view showing a rear end of the first sub-frame and a proximal portion of the ROPS. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in  FIGS. 1 and 2 , a self-propelled riding lawn mower has front wheels  1  in the form of a pair of right and left caster wheels, and rear wheels  2  in the form of a pair of right and left drivable running units. The lawn mower includes a body frame  10  carrying a motor section having an engine  3  positioned in a rear end portion of the vehicle body, a driving section having a driver&#39;s seat  4  disposed forwardly of the motor section, and a ROPS  5  disposed rearwardly of the driver&#39;s seat  4 . The lawn mower further includes a mower unit  7  connected to the body frame  10  between the front and rear wheels through a link mechanism  6 . 
     In this lawn mower, the link mechanism  6  is swung up and down relative to the body frame  10  by a single-acting lift cylinder  8  disposed below the driver&#39;s seat  4 , to move the mower unit  7  between a lower operative position where gauge wheels  7   b  disposed at the front and rear of a mower deck  7   a  of the mower unit  7  contact the ground, and an upper inoperative position where the gauge wheels  7   b  are raised above the ground. When the vehicle is operated to run with the mower unit  7  in the lower operative position, the mower unit  7  cuts grass with blades (not shown) arranged transversely in the mower deck  7   a  to rotatable about vertical axes by drive from the engine  3 , and discharges grass clippings through a grass outlet  7   c  disposed at one side of the mower deck  7   a . Details of the construction are as follows. 
     As shown in  FIGS. 3 and 4 , the body frame  10  includes a pair of right and left main body frames  11  extending longitudinally of the vehicle body, a front cross frame  12  interconnecting front ends of the right and left main body frames  11 , a propelling and working transmission device  13  interconnecting middle portions of the right and left main body frames  11 , a rear cross frame  14  interconnecting rear ends of the right and left main body frames  11 , and connecting frames  15  interconnecting the right and left main body frames  11  between the front cross frame  12  and the transmission device  13 . Each of the right and left main body frames  11  includes a first sub-frame  16  with a front end thereof connected to the front cross frame  12  and a rear end connected to the transmission device  13 , and a second sub-frame  17  with a front end thereof connected to the transmission device  13  and a rear end connected to the rear cross frame  14 . 
     The right and left front wheels  1  are supported by free ends of a front wheel support rod  18  connected in a middle position thereof, to be rotatable about an axis extending longitudinally of the vehicle body, to a front wheel support  12   a  disposed on the front cross frame  12 . The right and left rear wheels  2  are supported by rear axles  2   a  extending from the transmission device  13 . The link mechanism  6  is disposed between and supported by the first sub-frames  16  of the main body frames  11 . The driver&#39;s seat  4  is mounted on a seat support frame  19 , as shown in  FIG. 4 , connected between the rear ends of right and left first sub-frames  16 . The engine  3  is supported by engine mounting frames  3   a , as shown in  FIG. 3 , connected between the second sub-frames  17  of the main body frames  11  and the rear cross frames  14 . 
     As shown in  FIG. 5 , the ROPS  5  includes a pair of lower frames  5   a  fixed to opposite sides of the body frame  10 , respectively, an upper frame  5   b  interconnecting upper ends of the right and left lower frames  5   a  so that the upper frame  5   b  may be switched between an upstanding posture for use and a folded-down posture for storage, and a connecting frame  5   c  interconnecting intermediate positions of the right and left lower frames  5   a.    
     As shown in  FIGS. 6 and 7 , the transmission device  13  includes a transmission case  30  with an input shaft  31  projecting rearward from an upper part thereof, right and left HSTs  40  having casings  41  each connected at one side thereof to an upper part of one of opposite sides of the transmission case  30 , a reduction case  50  connected at an upper end portion thereof to an outward surface of the left HST  40  and having a lower end portion rotatably supporting the left rear axle  2   a , and a reduction case  50  connected at an upper end portion thereof to an outward surface of the right HST  40  and having a lower end portion rotatably supporting the right rear axle  2   a.    
     As shown in  FIG. 7 , the input shaft  31  of the transmission case  30  is interlocked to an output shaft  3   a  of the engine  3  through a rotary shaft  21 . The transmission case  30  houses a tubular propelling and branching transmission shaft  32  extending transversely of the vehicle body, and a gear mechanism  33  for transmitting drive from the input shaft  31  to this propelling transmission shaft  32 . A working power output shaft  34  extending longitudinally of the vehicle body is supported adjacent the lower end of the transmission case  30 , and a working power gear transmission mechanism  35  is disposed in the transmission case  30  to transmit drive from the input shaft  31  to the working power output shaft  34 . The working power output shaft  34  is, as shown in  FIG. 1 , interlocked through a rotary shaft  22  to an input shaft  7   d  disposed on the upper surface of the mower deck  7   a  of the mower unit  7 . 
     As shown in  FIGS. 6 and 7 , each of the right and left HSTs  40  has an axial plunger pump  43  of the variable displacement type and an axial plunger motor  44  of the fixed displacement type mounted in the casing  41 . The casing  41  includes a casing body  41   a  having a side surface, inwardly of the vehicle body, connected to a side of the transmission case  30 , and a base block  42  connected to an outward side surface of the casing body  41   a  to act as a port block. Ports of the pump  43  and the motor  44  are in communication with each other through an oil channel (not shown) formed in the base block  42 , i.e. port block  42 . That is, the HST is formed such that the motor  44  is driven by pressure oil from the pump  43 . As a result, each of the right and left HSTs  40 , is switchable between a forward drive state, a backward drive state and a neutral state by changing the swash plate angle of the pump  43 . In the forward drive state, drive from an input shaft  45  which is an input shaft of the pump  43  is made into forward drive, steplessly changed in speed and outputted from an output shaft  46  which is an output shaft of the motor  44 . In the backward drive state, the drive from the input shaft  45  is made into backward drive, steplessly changed in speed and outputted from the output shaft  46 . In the neutral state, the output from the output shaft  46  is stopped. 
     The input shaft  45  of the left HST  40  is splined to one end of the propelling transmission shaft  32  in the transmission case  30 , and the input shaft  45  of the right HST  40  is splined to the other end of the propelling transmission shaft  32 . Thus, the two input shafts  45  are rotatable with the propelling transmission shaft  32 . 
     As shown in  FIG. 8 , each of the reduction cases  50  for the right and left rear wheels includes a reduction case body  50   b  and the port block  42 . The reduction case body  50   b  has a side defining an opening  50   a  abutting on an outward surface of a lower portion of the port block  42  of the HST  40  and fastened with a plurality of connecting bolts, whereby the opening  50   a  is closed by the port block  42 . Each of the reduction cases  50  for the right and left rear wheels houses a gear type reduction mechanism  53  including an input gear  51  formed by cutting the output shaft  46  of the HST  40 , and an output gear  52  in engagement with this input gear  51  and splined to the rear axle  2   a  for unitary rotation. The input gear  51  and the output gear  52  of the reduction mechanism  53  have a reduction gear ratio therebetween. 
     With this structure, the transmission device  13  receives drive transmitted from the output shaft  3   a  of the engine  3  through the rotary shaft  21 , at the input shaft  31  of the transmission case  30  where the drive is divided for propulsion and for working by the gear mechanism  33  and the transmission mechanism  35 . The drive for propulsion is then divided and transmitted to the input shafts  45  of the right and left HSTs  40 , respectively, by the propelling and branching transmission shaft  32  of the transmission case  30 . The propelling drive transmitted to the left HST  40  is converted to forward or backward drive and steplessly changed in speed by the HST  40 , and inputted through the output shaft  46  to the left reduction case  50 . The drive is decelerated by the reduction mechanism  53  of the reduction case  50 , and transmitted to the left rear wheel  2  through the left rear axle  2   a . The propelling drive transmitted to the right HST  40  is converted to forward or backward drive and steplessly changed in speed by the HST  40 , and inputted through the output shaft  46  to the right reduction case  50 . The drive is decelerated by the reduction mechanism  53  of the reduction case  50 , and transmitted to the right rear wheel  2  through the right rear axle  2   a . The drive divided for working in the transmission case  30  is outputted forwardly of the vehicle body from the working power output shaft  34  through the rotary shaft  22  to the mower unit  7 . 
     In each of the right and left HSTs  40 , the swash plate angle of the pump  43  is changed by rocking a shift controller  47 , as shown in  FIG. 6 , positioned outwardly of the upper portion of the casing  41 . The shift controller  47  of the left HST  40  is interlocked through a link mechanism (not shown) to a left steering lever  23   a  of a pair of right and left steering levers  23   a  and  23   b  arranged in the driving section as shown in  FIG. 2 . The shift controller  47  of the right HST  40  is interlocked to the right steering lever  23   b  in the same way. 
     That is, rocking the right and left steering levers  23   a ,  23   b , respectively, longitudinally of the vehicle body, shifts the right and left HSTs  40  to drive the rear wheels  2  at the same speed forward or backward to cause the vehicle to run straight forward or backward, and further, to drive the rear wheels  2  at different speeds or in different directions to cause the vehicle to change its running direction. 
     As shown in  FIG. 7 , the working power transmission mechanism  35  in the transmission case  30  has a working clutch  36  for switching on and off transmission of the drive from the input shaft  31  to the working power output shaft  34 , thereby switching on and off the drive for the mower unit  7 . 
     As shown in  FIG. 8 , each of the right and left reduction cases  50  has a propelling brake  60  including a plurality of brake disks  61  mounted on the output shaft  46 . 
     Each of the right and left brakes  60  includes a plurality of friction plates  62  supported by a support portion  54  of the reduction case  50  and a control ring  63 , in addition to the brake disks  61 . Each of the brake disks  61  has a mounting bore with spline teeth mounted on the output shaft  46  to be slidable relative to and rotatable with the input gear  51  formed on the output shaft  46 . Each of the friction plates  62  is engaged with the support portion  54  to be slidable in directions along the output shaft  46 , but not rotatable relative to the support portion  54 . 
     That is, when a control lever  64  positioned outside the reduction case  50  is rocked about the axis of a rotary shaft  64   a , a control cam  65  attached to an end of the rotary shaft  64   a  to be rotatable therewith turns the control ring  63  through a preset angle of rotation. Then, the control ring  63  slides toward the brake disks  61  under the action of cam balls  66 , thereby pressing the brake disks  61  and the friction plates  62  to a support ring  67  fixed to the support portion  54 . The propelling brake  60  applies a frictional braking force to the brake disks  61 . This force is then applied through the input gear  51  and the output gear  52  to the rear wheel axle  2   a , thus braking the rear wheel  2 . 
     In each of the right and left HSTs  40 , the plunger capacity of the pump  43  is set to be smaller than that of motor  44 . Thus, at any forward or backward speed from the lowest to the highest, an oil delivery rate per rotation of the pump  43  is smaller than an oil drain rate per rotation of the motor  44 . In short, the output speed of each HST  40  is set to be low for the input speed even when HST  40  is shifted for the highest speed. 
     That is, as the HST  40  may fail to perform a satisfactory driving function when the speed of inputted torque is insufficient, it is necessary to input drive with a sufficient rotational frequency to the HST  40 . An adequate torque is thereby transmitted to the rear wheel  2  regardless of a speed state to which the HST  40  is shifted. Where this state of transmission were achieved solely through the deceleration by the reduction mechanism  53 , the reduction mechanism  53  would be required to provide an increased reduction ratio. This invention achieves such a state of transmission while allowing the reduction mechanism  53  to have a relatively small a reduction ratio, thereby to realize compactness of the reduction mechanism  53 . 
     The first sub-frames  16  and second sub-frames  17  of the right and left main body frames  11  are connected to the transmission device  13 , and the lower frames  5   a  of the ROPS  5  are fixed to the body frame  10  as shown in  FIGS. 9 through 11 . 
     Specifically, a rear end  16   a  of each first sub-frame  16  as shown in  FIG. 12  is fitted and fastened by connecting bolts  16   b  to an outward side surface of a portion  42   a  of the port block  42  of one of the right and left HSTs  40 , the portion  42   a  lying forwardly of the reduction case body  50   b  connected to the port block  42 . A front end  17   a  of each second sub-frame  17  is fitted to and fastened by connecting bolts  17   b  to an inward side surface of a portion  42   b  of the port block  42  of one of the right and left HSTs  40 , the portion  42   b  lying rearwardly of the casing body  41   a  connected to the port block  42 . 
     A proximal end  5   d  of each of the right and left lower frames  5   a  of the ROPS  5  is placed inwardly of the rear end  16   a  of one of the right and left first sub-frames  16 , and fastened along with the first sub-frames  16  to the front portion  42   a  of the port block  42  by the connecting bolts  16   b.    
     [Other Embodiments] 
     In the above embodiment, the reduction case  50  is mounted so that the rear axle  2   a  is positioned rearward of the input section. Consequently, the front end of the port block  42  is free from the connection with the reduction case body  50   b , and the rear end of the port block  42  is free from the connection with the casing body  41   a  of the HST  40 . Further, the rear end  16   a  of the first sub-frame  16  is connected to the portion  42   a  at the front end of the port block  42  free from the connection with the reduction case body  50   b . The front end of the second sub-frame  17   b  is connected to the portion at the rear end of the port block  42  free from the connection with the casing body  41   a  of the HST. On the other hand, where the reduction case  50  is mounted so that the rear axle  2   a  is positioned forward of the input section, the front end of the port block  42  is free from the connection with the casing body  41   a  of the HST  40 , and the rear end of the port block  42  is free from the connection with the reduction case body  50   b . Further, the rear end  16   a  of the first sub-frame  16  is connected to the portion, at the front end of the port block  42 , free from the connection with the casing body  41   a  of the HST. The front end of the second sub-frame  17  is connected to the portion, at the rear end of the port block  42 , free from the connection with the reduction case body  50   b . Thus, the first sub-frame  16  is called a first body frame  16  having one end, longitudinally of the vehicle body, connected to the portion  42   a  at one end, longitudinally of the vehicle body, of the port block  42 . The portion  42   a  is free from the connection with the reduction case body  50   b . Further, the second sub-frame  17  is called a second body frame  17  having the other end, longitudinally of the vehicle body, connected to the portion  42   b  at the other end, longitudinally of the vehicle body, of the port block  42 . The portion  42   b  is free from the connection with the casing body  41   a  of the HST. 
     This invention is applicable to various vehicles such as tractors and so forth, in addition to lawn mowers. The invention is applicable also to vehicles using crawler-type running units in place of rear wheels  2 . Lawn mowers, tractors and the like are collectively called herein a working vehicle, and rear wheels  2  and crawler-type running units are collectively called herein running units  2 .