Abstract:
A riding type mower comprises: a plurality of wheels including at least one driven wheel; a vehicle body supported by the plurality of wheels; a driver&#39;s seat supported by the vehicle body; a mower unit located below the vehicle body; a suspension mechanism for vertically movably supporting the mower unit from the vehicle body, the suspension mechanism having a restraint member operatively connected to the suspension mechanism; an operation mechanism for operating the suspension mechanism; a stopper for setting a lower limit for a vertical position of the mower unit to define a cutting height by abutment against the restraint member, the stopper is adapted to be rotated to change the lower limit; a lower limit adjustment element located laterally of the driver&#39;s seat and rotatable to rotate the stopper; and a linking mechanism for operatively connecting the lower limit adjustment element with the stopper.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to riding type mowers having a mower unit connected to the chassis thereof in such a manner as to be capable of freely moving upwards and downwards. 
         [0003]    2. Description of Related Art 
         [0004]    In conventional riding type mowers, a mower unit is moved downwards when an operation mechanism is operated, and when the moving device has moved downwards to a set height, a stopper acts, and downward motion of the mower unit stops. In this way, by simply operating the operation mechanism to a downward-movement side, conventional riding type mowers can accurately move a mower unit downward to a desired height set by a stopper. 
         [0005]    This type of riding type mower is presented, for example, in JP 2002-238325A (paragraphs 0033 and 0034; FIG. 2, FIG. 4, and FIG. 6). 
         [0006]    The mower disclosed therein is configured such that a hydraulic cylinder (equivalent to an operation mechanism) is linked to a mower constituting a mower unit through an action of an elevation link mechanism (equivalent to a linking mechanism), and when the elevation link mechanism is operated by the hydraulic cylinder, the mower is moved upwards and downwards with respect to a riding type vehicle (equivalent to a self-propelled chassis). Further, the configuration thereof is such that a stopper acts on a restraint pin provided in a drive arm of the elevation link mechanism, setting the limit of a swinging motion of the drive arm. As a result, a downward motion limit of the elevation link mechanism is set, and therefore, a downward motion limit of the mower is set. A lower limit adjustment mechanism is configured such that by rotating an adjustment knob disposed below a driving seat so as to adjust the stopper through rotation thereof, a height of a rotational stepwise stopper surface of the stopper is selected and the downward swinging motion limit of the drive arm is adjusted. 
         [0007]    When employing the above-described conventional technology, since an adjustment knob constituting a lower limit adjustment element for adjusting the stopper through rotation thereof is linked to the stopper such that the adjustment knob is rotated about an axis of rotation identical to an axis of rotation of the stopper, if the stopper is, for example, disposed so as to act on the linking mechanism of the mower unit and the operation mechanism, the lower limit adjustment element must be disposed below the driving seat, and therefore, the lower limit adjustment element becomes difficult to operate and lower limit adjustment of the moving device becomes difficult to perform. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an object of the present invention to provide a riding type mower allowing lower limit adjustment of a mower unit to be easily accomplished regardless of a position of a stopper. 
         [0009]    A riding type mower in accordance with the present invention comprises: a plurality of wheels including at least one driven wheel; a vehicle body supported by the plurality of wheels; a driver&#39;s seat supported by the vehicle body; a mower unit located below the vehicle body; a suspension mechanism for vertically movably supporting the mower unit from the vehicle body, the suspension mechanism having a restraint member operatively connected to the suspension mechanism; an operation mechanism for operating the suspension mechanism; a stopper for setting a lower limit for a vertical position of the mower unit to define a cutting height by abutment against the restraint member, the stopper is adapted to be rotated to change the lower limit; a lower limit adjustment element located laterally of the driver&#39;s seat and rotatable to rotate the stopper; and a linking mechanism for operatively connecting the lower limit adjustment element with the stopper. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a side view of an entire riding type mower. 
           [0011]      FIG. 2  is a plan view of an entire riding type mower. 
           [0012]      FIG. 3  is a side view of a mower unit and a link mechanism. 
           [0013]      FIG. 4  is a plan view of an arrangement section of an elevation cylinder and a lower limit adjustment element. 
           [0014]      FIG. 5  is a side view showing a linking condition of a raising pedal, a lowering pedal, and an elevation valve. 
           [0015]      FIG. 6  is a plan view showing a linking condition of a raising pedal, a lowering pedal, and an elevation valve. 
           [0016]      FIG. 7  is a side view showing an opening-closing structure of an opening-closing driving section floor. 
           [0017]      FIG. 8  is a side view showing an arrangement section of a stopper. 
           [0018]      FIG. 9  is a rear view of an adjustment linking mechanism. 
           [0019]      FIG. 10  is a plan view of a stopper arrangement section. 
           [0020]      FIG. 11  is a side view showing an application condition of a parking brake pedal. 
           [0021]      FIG. 12  is a rear view of an adjustment linking mechanism according to another embodiment. 
           [0022]      FIG. 13  is a rear view of an adjustment linking mechanism according to another embodiment. 
           [0023]      FIG. 14  is a rear view of an adjustment linking mechanism according to another embodiment. 
           [0024]      FIG. 15  is a side view of an elevation operation device according to another embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    The following is a description of embodiments of the present invention, with reference to the accompanying drawings. 
         [0026]    As shown in  FIG. 1  and  FIG. 2 , a riding type mower has a frame  3  of a self-propelled chassis providing a pair of caster type front wheels  1  disposed left and right in such a manner as to be capable of freely rotating, a pair of rear wheels  2  disposed left and right in such a manner as to be capable of being freely driven, a drive section  5  wherein an engine  4  provided at a rear-end section of the frame  3  is installed, a riding driving section  10  wherein a driving seat  11  disposed close to a front side of the drive section  5  is installed, and a topple protection frame  6  disposed close to a rear side of the driving seat; and is configured such that the frame  3  is connected with a mower unit  30  through an action of a link mechanism  20  disposed between the front and rear wheels of the frame  3 , and an output of the engine  4  is transferred to the mower unit  30  from a power take-off shaft  7   a  disposed in a transmission case  7  supported by the left and right rear wheels  2  through an action of a rotating shaft  8 . 
         [0027]    This mower performs lawn mowing and grass cutting operations, and when a hydraulic elevation cylinder  9  disposed below the driving seat  11  is operated, the elevation cylinder  9  performs raising and lowering operations of the link mechanism  20  with respect to the frame  3 , and as a result thereof, the mower unit  30  is lowered and raised respectively to a lowered operation condition wherein gauge wheels  32  disposed on front and rear sides of a cutting blade housing  31  make contact with a ground surface and a raised non-operation condition wherein the gauge wheels  32  are raised from the ground surface. When the mower unit  30  is set to the lowered operation condition and the self-propelled chassis is driven, the mower unit  30  performs cutting processing of a lawn or grass using cutting blades  33  driven so as to rotate about shafts oriented vertically within the cutting blade housing  31  in a plurality of locations therein, and the cut grass or lawn is conveyed to one side of the cutting blade housing  31  and discharged from a discharge opening  31 a to the exterior of the cutting blade housing  31  by wind generated by the rotation of the cutting blades  33 . 
         [0028]    As shown in  FIG. 2  etc., the riding driving section  10  of the self-propelled chassis is configured having the driving seat  11 , disposed between right and left rear wheel fenders  2   a,  a driving section floor  12  supported by the frame  3  in front of and below the driving seat  11 , and driver access openings  13  formed so as to provide driver steps  31   a  on both sides of the driving section floor  12  and at exactly or almost exactly the same height as the disposition height of the driving section floor  12 . 
         [0029]    Steering levers  14  are provided on both sides of the driving seat  11  of the riding driving section  10 , an accelerator lever  15  and an operation clutch lever  16  are provided on one side of the driving seat  11 , and a brake pedal  17   a,  a parking brake pedal  17   b,  a raising pedal  18 , and a lowering pedal  19  are provided at a front end side of the driving section floor  12 . 
         [0030]    The accelerator lever  15  performs acceleration operations of the engine  4 . In order to engage and disengage transmission of drive force from the engine  4  to the mower unit  30 , the operation clutch lever  16  performs clutching and declutching operations of an operation clutch (not shown) provided in the transmission case  7 , driving and stopping the mower unit  30 . The brake pedal  17   a  operates a drive-use brake (not shown) provided in the transmission case  7 , applying brakes to the left and right rear wheels  2 . As shown in  FIG. 11 , the parking brake pedal  17   b  engages a hook  17   c  thereof with an engagement piece  17   d  provided in the brake pedal  17   a,  maintaining the brake pedal  17   a  in a pressed-down condition, and as a result, the parking brake pedal  17   b  maintains the drive-use brake in an applied condition and applies parking brakes to the left and right rear wheels  2 . 
         [0031]    In order to transfer drive force from the engine  4  to each of the left and right rear wheels  2 ,  2 , the left and right steering levers  14  are each linked individually to speed variation sections of a pair of hydrostatic continuously variable transmission devices (not shown) provided in the transmission case  7 . When the left side steering lever  14  is swung in a fore-and-aft direction of the chassis, the hydrostatic continuously variable transmission device of the left rear wheel  2  performs speed variation, and when the right side steering lever  14  is swung in a fore-and-aft direction of the chassis, the hydrostatic continuously variable transmission device of the right rear wheel  2  performs speed variation. In this way, when both the left and right rear wheels  2 ,  2  are driven with an identical drive speed in a forward or backward direction, and self-propelled chassis can move forwards or backwards in a straight line, and by inducing a difference in the drive speed or the drive direction of the left and right rear wheels  2 ,  2 , the self-propelled vehicle can be driven in an arc towards the left or the right. 
         [0032]    As shown in  FIG. 1  and  FIG. 3 , the link mechanism  20  has a pair of left and right front swing links  22  supported at both outer sides of a front end section of the frame  3  by a rotating shaft  21  oriented in a transverse direction of the chassis in such a manner as to be capable of freely swinging, and rear swing links  24  supported at both outer sides of the frame  3  in the vicinity of the underside of the driving seat  11  by a rotating shaft  23  oriented in a transverse direction of the chassis in such a manner as to be capable of freely swinging. A lower end side of each of the left and right front swing links  22  is connected to a front linking bracket  34  of the cutting blade housing  31  in such a manner as to be capable of freely rotating, and a lower end side of each of the left and right rear swing links  24  is connected to a rear linking bracket  35  of the cutting blade housing  31  in such a manner as to be capable of freely rotating. In addition, a link  25  connected at a front end thereof to the left side front swing link  22  through an action of a linking pin  22   a  connecting the front swing link  22  to the front linking bracket  34  of the cutting blade housing  31 , and connected at a rear end thereof to the left side rear swing link  24  through an action of a linking pin  24   a  connecting the rear swing link  24  to the rear linking bracket  35  of the cutting blade housing  31  is provided, and a link  25  connected at a front end thereof to the right side front swing link  22  through an action of a linking pin  22   a  connecting the front swing link  22  in such a manner as to be capable of freely rotating to the front linking bracket  34  of the cutting blade housing  31 , and connected at a rear end thereof to the right side rear swing link  24  through an action of a linking pin  24   a  connecting the rear swing link  24  in such a manner as to be capable of freely rotating to the rear linking bracket  35  of the cutting blade housing  31  is provided. 
         [0033]    As shown in  FIG. 3  and  FIG. 4 , a link drive arm  26  extends towards the rear of the chassis from a section of the rotating shaft  23  of the rear swing links  24  disposed between a pair of left and right chassis main frames  3   a,  and the cylinder rod of the elevation cylinder  9  is connected to the link drive arm  26 . 
         [0034]    As a result, the link mechanism  20  connects the mower unit  30  to the frame  3  in such a manner as to be capable of freely moving upwards and downwards. The elevation cylinder  9  connects the link mechanism  20  to the cutting blade housing  31  of the mower unit  30  as a linking mechanism such that the mower unit  30  can be raised and lowered. That is to say, by extending and contracting, the elevation cylinder  9  rotates the rotating shaft  23  through an action of the link drive arm  26  and swings the left and right rear swing links  24  upward and downward with respect to the frame  3 , and using the left and right rear swing links  24 , swings the left and right front swing links  22  upward and downward with respect to the frame  3  through an action of the link  25 , raising and lowering the mower unit  30  with respect to the self-propelled chassis. 
         [0035]    As shown in  FIG. 5 ,  FIG. 6 , and  FIG. 7 , an elevation valve  40  connected to a supply and removal port of the elevation cylinder  9  through an action of a hydraulic hose (not shown) is provided at a front section of the transmission case  7  in order to operate the elevation cylinder  9 , and an operation arm  40   a  capable of freely swinging about a shaft of the elevation valve  40  oriented in a vertical direction of the chassis is linked to the raising pedal  18  and the lowering pedal  19  disposed in the riding driving section  10  through an action of a link rod  41  etc. 
         [0036]    As shown in  FIG. 6  and  FIG. 7 , the raising pedal  18  is supported by a rear arm section  43   a,  of a pedal arm  43 , extending towards the rear of the chassis from a pedal shaft  42 , wherein the pedal shaft  42  is supported below the driving section floor  12  in a transverse direction of the chassis by the left and right chassis main frames  3   a  in such a manner as to be capable of freely rotating, and the pedal arm  43  is supported at a center section thereof by the pedal shaft  42  in such a manner as to be capable of freely rotating with respect to the pedal shaft  42 . The lowering pedal  19  is supported by a rear arm section  43   b,  of the pedal arm  43 , extending towards the front of the chassis from the pedal shaft  42 . The pedal shaft  42  supports the brake pedal  17   a  in such a manner as to be capable of freely rotating as one with the pedal shaft  42 . The pedal shaft  42  is linked to left and right driving brake operation sections  17  disposed in the transmission case  7  by a link rod  48 , linking the brake pedal  17   a  to both of the driving brake operation sections  17 . 
         [0037]    As shown in  FIG. 6  and  FIG. 7  etc., a front end side of the link rod  41  is connected to the mounting member  44  in such a manner as to be capable of freely rotating with respect to a mounting member  44 , wherein the mounting member  44  facilitates the supporting of the pedal arm  43  by the pedal shaft  42  in such a manner as to be capable of freely rotating relative to the pedal shaft  42 , and rotates relative to the pedal shaft  42  together with the pedal arm  43 . A rear end side of the link rod  41  is connected to the operation arm  40   a  of the elevation valve  40  in such a manner as to be capable of freely rotating with respect to the operation arm  40   a.    
         [0038]    As a result, both the raising pedal  18  and the lowering pedal  19  are supported by the same pedal arm  43  in such a manner as to be capable of freely rotating as one. The raising pedal  18 , as a result of pressing-down thereof, swings downwards about an axis of the pedal shaft  42 , rotates the mounting member  44  in one direction, transfers the operation force thereof to the operation arm  40   a  of the elevation valve  40  using the link rod  41 , and switches the elevation valve  40  from a neutral condition to a raising condition. Furthermore, the lowering pedal  19 , as a result of pressing-down thereof, swings downwards about an axis of the pedal shaft  42 , rotates the mounting member  44  in the other direction, transfers the operation force thereof to the operation arm  40   a  of the elevation valve  40  using the link rod  41 , and switches the elevation valve  40  from a neutral condition to a lowering condition. Both the raising pedal  18  and the lowering pedal  19 , as a result of cancellation of the pressing-down operation, return independently to the non-operation conditions thereof and restore the elevation valve  40  to the neutral position thereof as a result of a neutral restoration force provided such that the elevation valve  40  can return independently to the neutral position. 
         [0039]    As shown in  FIG. 8 ,  FIG. 9 , and  FIG. 10 , a stopper  50  of an approximately circular shape when viewed from above or below the chassis is provided at a position more towards the inside of the chassis than one of the chassis main frames  3   a.  The stopper  50  is supported through an action of a rotating shaft  52  by a support bracket  51  of a link frame  3   b  connected to the left and right chassis main frames  3   a,  and furthermore, a plurality of stopper surfaces  50   a  are provided circumferentially side-by-side on an upper surface side of the stopper  50 . A lowering restraint arm (restraint arm)  53  connected to the rotating shaft  23  of the rear swing links  24  in such a manner as to be capable of freely rotating as one therewith and swinging downward about an axis of the rotating shaft  23  pursuant to lowering of the mower unit  30  by the elevation cylinder  9  and rotation of the rotating shaft  23  is caught and supported by one of the plurality of stopper surfaces  50   a.  Accordingly, the stopper  50  acts to stop the lowering restraint arm  53  through an action of one of the stopper surfaces  50   a,  setting a rotation limit of the rotating shaft  52 , and as a result, the stopper  50  sets a downward motion limit of the rear swing links  24  and the front swing links  22 , setting a downward motion limit of the mower unit  30  by the elevation cylinder  9 . 
         [0040]    As clearly shown in  FIG. 8  and  FIG. 9 , the plurality of stopper surfaces  50   a  of the stopper  50  are disposed in a stepwise format such that a height (above-ground height) from each stopper surface  50   a  to the support bracket  51  is different. The stopper  50  is supported in such a manner as to be capable of freely rotating with respect to the support bracket  51  together with the rotating shaft  52  oriented in a vertical direction of the chassis, and is configured so as to be capable of being adjusted through rotation by, as shown in  FIG. 2  and  FIG. 4 , a lower limit adjustment element  54  provided at a side of the driving seat  11  of the riding driving section  10  and more towards the outside of the chassis than one of the chassis main frames  3   a.    
         [0041]    That is to say, as shown in  FIG. 8  and  FIG. 9  etc., the lower limit adjustment element  54  is supported through an action of a rotating shaft  56  in such a manner as to be capable of freely rotating on an upper surface side of a control panel  55  supported by one of the chassis main frames  3   a.    
         [0042]    An adjustment linking mechanism  59  configured so as to be linked to the lower limit adjustment element  54  and the stopper  50  comprises the rotating shaft  56 , a link gear  57  provided at a lower end side of the rotating shaft  56 , and a rotation gear  58  provided in such a manner as to be capable of freely rotating as one with the stopper  50  through the support thereof on an upper end side of the rotating shaft  52  of the stopper  50  in such a manner as to be capable of freely rotating as one with the rotating shaft  52 . 
         [0043]    The link gear  57  is connected to the rotating shaft  56  in such a manner as to be capable of freely rotating as one therewith, and the rotating shaft  56  is connected to the lower limit adjustment element  54  as a linking rotating shaft in such a manner as to be capable of freely rotating as one therewith. The link gear  57  and the rotating gear  58  are mutually engaged and rotate in a mutually linked manner. 
         [0044]    That is to say, the stopper  50  is disposed more towards the inside of the chassis than the chassis main frames  3   a  in order to act upon the rotating shaft  23  of the rear swing links  24  within the link mechanism  20 ; the lower limit adjustment element  54  is disposed more towards the outside of the chassis than the chassis main frames  3   a  in order to be positioned at a side of the driving seat  11 ; and the lower limit adjustment element  54  and the stopper  50  are disposed such that an axis of rotation X 1  oriented in a vertical direction of the chassis and constituted by the axis of the rotating shaft  56  of the lower limit adjustment element  54  and an axis of rotation X 2  oriented in a vertical direction of the chassis and constituted by the axis of the rotating shaft  52  of the stopper  50  are in an eccentric condition. For this reason, the adjustment linking mechanism  59  links the lower limit adjustment element  54  and the stopper  50  while permitting the eccentricity of the axis of rotation X 1  of the lower limit adjustment element  54  and the axis of rotation X 2  of the stopper  50  through the linking of the rotation gear  58  and the link gear  57 . 
         [0045]    Accordingly, when the lower limit adjustment element  54  is rotated about the axis of rotation X 1 , the operation force thereof is transferred to the rotating shaft  52  of the stopper  50  by the adjustment linking mechanism  59 ; the stopper  50  rotates about the axis of rotation X 2  in a rotation direction corresponding to a rotation direction of the lower limit adjustment element  54  and through a rotation angle corresponding exactly to a rotation angle of the lower limit adjustment element  54 ; and among the plurality of stopper surfaces  50   a,  the stopper surface  50   a  corresponding to the operation position of the lower limit adjustment element  54  is adjusted through rotation to a mounting condition wherein the stopper surface  50   a  acts upon the lowering restraint arm  53 . 
         [0046]    That is to say, when the grass or lawn cutting height is to be changed during the execution of grass cutting or lawn cutting operations, by adjusting a mounting height of gauge wheel shafts  32   a  (see  FIG. 3 ) of the front and rear gauge wheels  32  with respect to brackets  36 , the mounting height of each gauge wheel  32  with respect to the cutting blade housing  31  is set to a suitable mounting height corresponding to the desired cutting height of the lawn or grass. Then, the lower limit adjustment element  54  is rotated and the stopper  50  is adjusted through rotation to a suitable mounting condition wherein among the stopper surfaces  50   a  of the stopper  50 , the stopper surface  50   a  corresponding to the set mounting height of the gauge wheels  32  acts. Then, when the lowering pedal  19  is pressed down, the elevation valve  40  is switched from the neutral condition to the lowering condition and the elevation cylinder  9  operates towards a contraction side as a result of the operating force thereof, the elevation cylinder  9  swings the link mechanism  20  to a downward side, lowering the mower unit  30 , and the mower unit  30  adopts a lowered operation condition in contact with a ground surface through the front and rear gauge wheels  32 . At this time, the stopper  50  acts to stop the lowering restraint arm  53  through an action of the stopper surface  50   a  selected through rotation of the lower limit adjustment element  54 , and lowering of the mower unit  30  by the elevation cylinder  9  is stopped in accordance with the fact that the elevation cylinder  9  has lowered the mower unit  30  to the downward motion limit. As a result, the linking pins  22   a  connecting the left and right front swing links  22  to the front linking bracket  34  of the cutting blade housing  31  are positioned at an upper section side or an upper end of long pin holes  34   a  (see  FIG. 3 ) of the front linking bracket  34 , and the linking pins  24   a  connecting the left and right rear swing links  24  to the rear linking bracket  35  of the cutting blade housing  31  are positioned at an upper section side or an upper end of long pin holes  35 a (see  FIG. 3 ) of the rear linking bracket  35 , and therefore, when the front and rear gauge wheels  32  or a ride-over roller  37  (see  FIG. 3 ) of the mower unit  30  travel onto a protrusion in the ground surface or an obstacle, the mowing operation can continue as the mower unit  30  is capable of moving upwards with respect to the left and right front swing links  22  and rear swing links  24  in order to be raised with respect to the self-propelled chassis by the lifting operation of the ground. 
         [0047]    When relocating or cornering, the raising pedal  18  is pressed downward. As a result, the elevation valve  40  is switched from the neutral condition to the raising condition and the elevation cylinder  9  is operated towards an extension side as a result of the operating force thereof, the elevation cylinder  9  swings the link mechanism  20  to an upward side and raises the mower unit  30 , and the mower unit  30  adopts a raised non-operation condition wherein the front and rear gauge wheels  32  are raised up from the ground surface. 
         [0048]    As shown in  FIG. 6  etc., the raising pedal  18  and the lowering pedal  19  are disposed on the side opposite to the parking brake pedal  17   b  with respect to the brake pedal  17   a  of the driving section floor  12 , and in a distributed condition at a front side and rear side of the chassis. More specifically, as shown in  FIG. 2 , when viewed from above or below the chassis, the raising pedal  18  and the lowering pedal  19  are disposed in a distributed condition with respect to a fore-and-aft direction of the chassis wherein the raising pedal  18  is lined up with the driver access openings  13  in a transverse direction of the chassis, and the lowering pedal  19  is displaced from the raising pedal  18  towards a front side of the chassis and disposed slightly closer to a front side of the chassis than the driver access openings  13 . 
         [0049]    That is to say, each of the raising pedal  18  and the lowering pedal  19  are operated by a single foot. However, as the lowering pedal  19  is operated closer to a front side than the raising pedal  18  and the raising pedal  18  is operated closer to a rear side than the lowering pedal  19 , pedal operations are performed with little possibility of incorrect operation occurring as a result of operating a pedal other than that intended. Furthermore, when getting on or off via the driver access openings  13 , a situation wherein the lowering pedal  19  is mistakenly pressed down and the mower unit  30  is lowered is less likely to occur than a situation wherein the raising pedal  18  is mistakenly pressed down and the mower unit  30  is raised. 
         [0050]    As shown in  FIG. 2 , the driving section floor  12  is partitioned into an opening-closing driving section floor  12   a  and a fixed driving section floor  12   b  by a partition line B 1  passing between the raising pedal  18  and the lowering pedal  19  in a transverse direction of the chassis and partition lines B 2  disposed in a fore-and-aft direction of the chassis on an inner side with respect to the driver steps  31   a.  As shown in  FIG. 7 , the opening-closing driving section floor  12   a  is supported in such a manner as to be capable of freely opening and closing by swinging upwards and downwards about an axis P disposed in a transverse direction of the chassis in an end section of the opening-closing driving section floor  12   a  positioned towards the rear of the chassis. 
         [0051]    That is to say, by raising and opening the opening-closing driving section floor  12   a,  the section below the driving section floor is opened and the upper surface side of the cutting blade housing  31  can be inspected and repaired from the upper side of the self-propelled chassis via the installation space of the opening-closing driving section floor  12   a.    
         [0052]      FIG. 12  shows an adjustment linking mechanism  59  according to another embodiment. The adjustment linking mechanism  59  is configured so as to provide a flexible drive cable  60  linked at one end side thereof to the stopper  50  in such a manner as to be capable of freely rotating as one with the stopper  50  and linked at the other end side thereof to the lower limit adjustment element  54  in such a manner as to be capable of freely rotating as one with the lower limit adjustment element  54 ; the stopper  50  and the lower limit adjustment element  54  are linked as a result of a linking action of the flexible drive cable  60 ; and the eccentricity of the axis of rotation X 2  of the stopper  50  and the axis of rotation X 1  of the lower limit adjustment element  54  is permitted through flexure of the flexible drive cable  60 . The flexible drive cable  60  passes through a penetration of the chassis main frame  3   a.    
         [0053]      FIG. 13  shows an adjustment linking mechanism  59  according to yet another embodiment. The adjustment linking mechanism  59  is configured so as to provide a rotating shaft  62  linked at one end side thereof to the stopper  50  through an action of a universal joint  61  and linked at the other end side thereof to the rotating shaft  56  of the lower limit adjustment element  54  through an action of a universal joint  61 ; the stopper  50  and the lower limit adjustment element  54  are linked as a result of a linking action of the universal joints  61  and the rotating shaft  62 ; and the eccentricity of the axis of rotation X 2  of the stopper  50  and the axis of rotation X 1  of the lower limit adjustment element  54  is permitted through flexure of the universal joints  61 . The rotating shaft  62  passes through a penetration of the chassis main frame  3   a.    
         [0054]      FIG. 14  shows an adjustment linking mechanism  59  according to yet another embodiment. The adjustment linking mechanism  59  is configured having a stopper-side bevel gear shaped rotating gear  65  provided in such a manner as to be capable of freely rotating as one with the rotating shaft  52  of the stopper  50 , a bevel gear shaped drive gear  66  on the adjustment element side mutually engaging with the rotating gear  65 , and a rotating shaft  56  of the lower limit adjustment element  54  provided as a rotating shaft linking the drive gear  66  to the lower limit adjustment element  54 . Through an action of the bevel gear shaped transmission gears  65  and  66 , the adjustment linking mechanism  59  enables the axis of rotation X 1  of the lower limit adjustment element  54  to be disposed at a position displaced from the axis of rotation X 2  of the stopper  50  towards an outer side with respect to the driving seat  11  and to be inclined with respect to the axis of rotation X 2  of the stopper  50 , and the adjustment linking mechanism  59  links the stopper  50  and the lower limit adjustment element  54 . 
         [0055]      FIG. 15  is a side view of an elevation operation device according to another embodiment, for raising and lowering a mower unit  30 . As shown in this figure, the elevation operation device has an operation arm  67  provided on the rotating shaft  23  of the rear swing links  24  in such a manner as to be capable of freely rotating as one with the rotating shaft  23 , a swing arm  69  linked to the operation arm  67  through an action of an auxiliary link  68 , and an elevation lever  71  extending from a rotating shaft  70  of the swing arm  69 . 
         [0056]    That is to say, the elevation lever  71  is lowered manually about an axis of the rotating shaft  70  to a “Lower” position. As a result, the rotating shaft  70  rotates, the swing arm  69  swings downwards, and the rotating shaft  23  rotates through an action of the auxiliary link  68  and the operation arm  67 . The front swing links  22  swing downwards pursuant to the resultant downward swinging of the rear swing links  24 , and the mower unit  30  is lowered. 
         [0057]    Alternatively, the elevation lever  71  is raised manually about the axis of the rotating shaft  70  to a “Raise” position. As a result, the rotating shaft  70  rotates, the swing arm  69  swings upwards, and the rotating shaft  23  rotates through an action of the auxiliary link  68  and the operation arm  67 . The front swing links  22  swing upwards pursuant to the resultant upward swinging of the rear swing links  24 , and the mower unit  30  is raised. 
       Other Embodiment 
       [0058]    As an alternative to the configuration of the mower unit  30  in accordance with the above-described embodiments such that the mower unit  30  is raised and lowered by an elevation cylinder  9 , embodiments configured so as to perform raising and lowering using hydraulic motors and various other kinds of actuators also accomplish the object of the present invention. Therefore, the elevation cylinder  9 , a hydraulic motor, and the elevation lever  71 , etc. are commonly referred to as the operation mechanisms  9 ,  71 . 
         [0059]    In lieu of the link mechanism, other suspension mechanisms such as one utilizing chains may be used with the present invention.