Abstract:
A walk-behind cultivator has a body, at least one pair of first tine assemblies mounted on the body to undergo rotation about a rotational axis in a first direction of rotation, and at least one pair of second tine assemblies mounted to undergo rotation about the rotational axis in a second direction of rotation different from the first direction of rotation. Each of the first tine assemblies has first tines connected together along end portions thereof. Each of the second tine assemblies has second tines connected together along end portions thereof. The second tine assemblies are arranged in the same phase with respect to each other around the rotational axis.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an improvement in walk-behind cultivators. 
     BACKGROUND OF THE INVENTION 
     Common walk-behind cultivators operate by rotation of tillage tines provided on rotor shafts, being propelled with the tillage tines. Those cultivators are called front-tine cultivators. In recent years, however, front-rotary cultivators, that is, walk-behind cultivators with tillage tines arranged forward of the bodies provided with driving wheels have been developed. 
     Having the tillage tines at the front of the bodies, the front-rotary cultivators facilitate cultivation in headlands, allowing operators to look forward during operation, providing good workability, and thus attracting attention (See, e.g., Japanese Patent No. 3015821 and Japanese Utility Model Laid-Open Publication No. SHO-56-97903). 
     The words “headlands” mean areas left unplowed by a cultivator cultivating a rectangular-shaped field, moving back and forth in parallel with one side thereof, for example, because it temporarily stops working at the opposite ends of the field for turning or the like. 
     A cultivator in Japanese Patent No. 3015821 is called a down-cut cultivator with tillage tines rotated from the upper front of a traveling direction toward the ground and is mainly used to break up soil. 
     A cultivator in Japanese Utility Model Laid-Open Publication No. SHO-56-97903 is called an up-cut cultivator with tillage tines rotated from the upper rear of a traveling direction toward the ground and is mainly used to weed a field. 
     As an example of such front-rotary cultivators, the cultivator of Japanese Patent No. 3015821 will be generally described with reference to FIG. 16 hereof. 
     A front-rotary cultivator  200  shown in FIG. 16 is a walk-behind cultivator with a transmission case  203  provided below a body  202  to which an engine  201  is mounted, the transmission case  203  being integrally molded with a rear mission case  204  and a front rotary case  205 , a pair of left and right driving wheels  207 ,  207  mounted on an axle  206  protruded from a rear portion of the mission case  204 , a rotary countershaft  208  provided in a front portion of the mission case  204 , a plurality of tillage tines  210  mounted on a rotor shaft  209  protruded from a front portion of the rotary case  205 , and a chain  213  running in the rotary case  205  between a driving sprocket  211  of the rotary countershaft  208  and a driven sprocket  212  of the rotor shaft  209 . 
     The engine  201  is a horizontal engine with an output shaft  214  protruded laterally. A belt  218  runs between a driving pulley  215  mounted on the output shaft  214  and a driven pulley  217  mounted on an input shaft  216  protruded from the side of the mission case  204  to transmit the power of the engine  201  to the transmission. The power of the engine  201  can thus drive the pair of left and right driving wheels  207 ,  207  via the axle  206  and drive the tillage tines  210  via the rotary countershaft  208 , chain  213  and rotor shaft  209 . 
     The tillage tines  210  of the front-rotary cultivator  200  are arranged in four rows across the width of the body  202  (across the two sides of the figure sheet). All the tillage tines  210  rotate with the rotor shaft  209  in one direction for cultivation. Reference numeral  219  denotes a tension roller as a main clutch and  220  a handle bar. 
     Cultivation with the tillage tines  210  can cause a so-called dashing phenomenon (or jumping phenomenon) in which the cultivation reaction force causes the tillage tines  210  to bound upward. The dashing phenomenon caused reduces the linearity in travel of the cultivator  200 , resulting in insufficient cultivation performance and poor finish of cultivation. This tendency is more noticeable especially as the cultivator  200  is lighter in weight. 
     The above conventional art arranges the engine  201  between the rear axle  206  and the front rotor shaft  209  to shift the center of gravity of the cultivator  200  forward, thereby to apply part of the weight of the engine  201  to the tillage tines  210 . As a result, the degree of digging of the tillage tines  210  into the ground Gr 21  can be somewhat increased and the occurrence of the dashing phenomenon can be somewhat prevented. 
     Only with such a structure, however, there is a limit to the increase in degree of digging of the tillage tines  210  and the prevention of the dashing phenomenon. To solve the problem, it seems possible to arrange the engine  201  or a heavy load such as a counterweight in front of or above the tillage tines  210  to increase the distribution of weight to the tillage tines  210 . The center of gravity of the cultivator  200  is, however, too much offset forward, making the handle bar  220  heavier. Especially in the operation of pushing down the handle bar  220  to lift the tillage tines  210  to turn the cultivator  200 , the pushing-down force is increased, reducing the operability. Only changing the center of gravity of the cultivator  200  forward thus inexpediently increases the workload of the operator. 
     Thus desired is a front-rotary cultivator with tillage tines arranged at the front of the body equipped with driving wheels, being able to prevent the occurrence of the dashing phenomenon, increase cultivation performance and also reduce the workload of the operator. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a walk-behind cultivator, which comprises: a body; an engine provided on the body; left and right driving wheels provided to the body and driven by the engine; and a plurality of tillage tines provided at the front of the body and driven by the engine, the tillage tines comprising: a plurality of forward-rotating tines arranged in the center of the width of the body; and a plurality of reverse-rotating tines arranged outward of the forward-rotating tines in the transverse direction of the body, the reverse-rotating tines being arranged in the same phase in a side view. 
     Arranging the forward-rotating tines of the tillage tines in the center of the body width and arranging the reverse-rotating tines transversely outward of the forward-rotating tines allow the forward-rotating tines to (forwardly) rotate from the upper front of the traveling direction toward the ground and the reverse-rotating tines to (reversely) rotate from the upper rear of the traveling direction toward the ground. 
     The direction of the cultivation reaction forces against the forward-rotating tines is forward and upward of the traveling direction of the walk-behind cultivator, that is, opposite to the rotation direction of the forward-rotating tines. The direction of the cultivation reaction forces against the reverse-rotating tines is rearward of the traveling direction of the walk-behind cultivator, that is, opposite to the rotation direction of the reverse-rotating tines. The cultivation reaction forces against the forward-rotating tines and the cultivation reaction forces against the reverse-rotating tines act in opposite directions. 
     When all the tillage tines are forward-rotating tines, the cultivation reaction force is larger, making it difficult to prevent the occurrence of a dashing phenomenon due to the cultivation reaction force. In this invention, the cultivation reaction force arising from cultivation with the forward-rotating tines can be cancelled to some extent by the cultivation reaction force arising from cultivation with the reverse-rotating tines. As a result, the occurrence of a dashing phenomenon can be prevented. 
     With the walk-behind cultivator being propelled, the forward-rotating tines in the center of the body width can rotate forward to dig into the ground for cultivation, digging out the cultivated soil rearward of the cultivator body. 
     Arranging the reverse-rotating tines in the same phase in a side view allows the reverse-rotating tines arranged transversely outward of the forward-rotating tines to rotate reversely, with the walk-behind cultivator being propelled, to simultaneously dig into the ground, digging out the cultivated soil forward of the cultivator body. 
     Simultaneous digging of the reverse-rotating tines into the ground can also increase the degree of digging as compared with differential digging. As a result, the depth of plowing with the reverse-rotating tines is increased, increasing cultivation performance. 
     Simultaneous digging of the reverse-rotating tines into the ground can make the cultivation reaction forces against the reverse-rotating tines approximately equal. The approximately equal cultivation reaction forces can prevent the unbalanced occurrence of a dashing phenomenon and also prevent the occurrence of a pitching phenomenon (phenomenon in which the cultivator swings back and forth like a seesaw). This prevents snaking of the cultivator, increasing its travel linearity, steerage and workability, and improving cultivation finish. 
     Even when the cultivator has a light weight, it is not necessary to dispose the engine or a heavy load such as a counterweight in front of or above the tillage tines, increasing the weight distribution to the tillage tines so as to increase the degree of digging of the tillage tines to prevent a dashing phenomenon. Therefore, in the operation of pushing down an operating handle to lift the tillage tines during turn of the cultivator, the pushing down force is not increased. This can reduce the workload of the operator, increasing steerage. 
     In this invention, the forward-rotating tines are preferably arranged in the same phase in a side view. 
     Arranging the forward-rotating tines in the same phase in a side view and arranging the reverse-rotating tines in the same phase in a side view allow the forward-rotating tines in the center of the body width to, with the walk-behind cultivator being propelled, forwardly rotate to simultaneously dig into the ground for cultivation, digging out the cultivated soil rearward of the cultivator body. The reverse-rotating tines arranged transversely outward of the forward-rotating tines are allowed to rotate reversely to simultaneously dig into the ground, digging out the cultivated soil forward of the cultivator body. 
     The simultaneous digging of the forward-rotating tines into the ground can increase the degree of digging as compared with differential digging. The simultaneous digging of the reverse-rotating tines into the ground can also increase the degree of digging. This results in an increase in the depth of plowing with the forward-rotating tines and the reverse-rotating tines, further increasing cultivation performance. 
     Further, simultaneous digging of the forward-rotating tines into the ground can make the cultivation reaction forces against the forward-rotating tines approximately equal. The same applies to the reverse-rotating tines. The approximately equal cultivation reaction forces allow further prevention of the unbalanced occurrence of a dashing phenomenon and also allow prevention of the occurrence of a pitching phenomenon (phenomenon in which the cultivator swings back and forth like a seesaw). 
     Furthermore, the simultaneous digging of the forward-rotating tines into the ground with the simultaneous digging of the reverse-rotating tines into the ground can make approximately equal the left and right cultivation reaction forces acting on the cultivator. This also enables preventing the occurrence of a rolling phenomenon (phenomenon in which the cultivator rolls around the longitudinal axis passing through the center of gravity of the cultivator). This can further prevent snaking of the cultivator, increasing travel linearity and steerage, further increasing the workability, and also improving cultivation finish. 
     Further, in this invention, the left and right driving wheels are preferably arranged rearward of the reverse-rotating tines. In the cultivator of the present invention adopting the front-rotary system, the driving wheels are arranged rearward of the tillage tines. Arranging the driving wheels rearward of the reverse-rotating tines to dig out the cultivated soil forward of the cultivator body allows the driving wheels to run over the ground dug down with the reverse-rotating tines. This can increase the degree of settling of the driving wheels, maintaining the cultivator horizontally. Thus stable cultivation is provided. Since the position of the engine is also horizontal, the oil surface of a lubricant in the engine is not slanted. Thus smooth lubrication of the engine is provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is a left side view of a front-rotary cultivator according to the present invention; 
     FIG. 2 is a cross-sectional view of an engine, a main clutch, a transmission case and the surroundings according to the invention; 
     FIG. 3 is a cross-sectional view of the main clutch according to the invention; 
     FIG. 4 is a plan view of the main clutch according to the invention; 
     FIG. 5 is a cross-sectional view taken along line  5 — 5  in FIG. 5; 
     FIG. 6 is a cross-sectional view taken along line  6 — 6  in FIG. 2; 
     FIG. 7 is a front view of the front-rotary cultivator according to the invention; 
     FIGS. 8A and 8B are structural diagrams of a rotary working unit according to the invention; 
     FIGS. 9,  10  and  11  are functional diagrams of a cultivation power transmission mechanism according to the invention; 
     FIG. 12 is a functional diagram of the front-rotary cultivator according to the invention; 
     FIG. 13 is a diagram of the tilted state of the front-rotary cultivator according to the invention; 
     FIG. 14A is a perspective view illustrating a modification of the rotary working unit according to the invention; FIG. 14B is a view taken from the direction of an arrow  14 B in FIG. 14A; and FIG. 14C is a view taken from the direction of an arrow  14 C in FIG. 14A; 
     FIG. 15 is a functional diagram of a front-rotary cultivator with the modification shown in FIG. 14A; and 
     FIG. 16 is a schematic diagram of a conventional front-rotary cultivator. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A front-rotary cultivator  10  shown in FIG. 1 is a small walk-behind self-propelled cultivator with a rotary working unit  120  arranged at the front of a transmission case  58  provided with left and right driving wheels  11 ,  11  (See FIG.  7 ). 
     Specifically, the front-rotary cultivator (hereinafter referred to merely as a “cultivator”)  10  is a walk-behind cultivator with the driving wheels  11 ,  11  provided at the transmission case  58  as the body and with the rotary working unit  120  provided at the front of the transmission case  58 . The driving wheels  11  and the rotary working unit  120  are driven by an engine  20  provided on the transmission case  58 . 
     More specifically, FIG. 1 shows that the transmission case  58  is arranged below the engine  20  via a main clutch  30  and output shafts  53  and  57  are protruded from front and rear portions of the transmission case  58 . The front output shaft (rotary countershaft)  53  drives the rotary working unit  120  and the rear output shaft (axle)  57  drives the driving wheels  11 . It is thus possible to arrange the driving wheels  11 ,  11  at the rear of the transmission case  58  and arrange the rotary working unit  120  at the front of the transmission case  58 . 
     The engine  20  as a power source is a vertical engine having an output shaft (crankshaft)  21  oriented substantially vertically, cylinders  22  extended substantially horizontally forward, and an oil tank  23  provided at its rear. 
     The cultivator  10  has an operating handle  12  extended from the rear of a clutch case  34  of the main clutch  30  in a rearward and upward direction. The operating handle  12  is provided with a clutch lever  13 . The clutch lever  13  is for operating the main clutch  30 . In the figure, reference numeral  14  denotes a soil scattering-prevention cover. 
     FIG. 2 is a cross-sectional view of an engine, a main clutch, a transmission case and the surroundings according to the present invention taken from the left side, showing the configuration in which the output shaft  21  of the engine  20  is protruded downward and a transmission  50  is coupled to the lower end of the output shaft  21  via the main clutch  30 . 
     The upper end of the clutch case  34  is bolted to the lower end of a body  25  of the engine  20  and the transmission case  58  of the transmission  50  is bolted to the lower end of the clutch case  34 , so that the clutch case  34  and the transmission case  58  serve as the cultivator body. 
     FIG. 3 shows in section the main clutch  30  shown in FIG.  2 . 
     The main clutch  30  includes a sun gear  31  mounted on the output shaft  21  of the engine  20 , a planet gear assembly  32  engaged with the sun gear  31 , an internal gear  33  engaged with the planet gear assembly  32 , the clutch case  34  housing the sun gear  31 , planetary gear assembly  32  and internal gear  33 , a plurality of balls  35  interposed between the internal gear  33  and the clutch case  34 , and a brake  36  for locking/unlocking the internal gear  33 . 
     The planet gear assembly  32  includes a plurality of planet gears  37  engaged with the sun gear  31  and the internal gear  33 , and a planet frame  38  rotatably supporting the planet gears  37 . The planet frame  38  is at its center provided with a coupling  39  spline-coupled to an input shaft  51  of the transmission  50 . 
     The internal gear  33  includes teeth  33   a  engaged with the planet gears  37  and a cylinder  33   b  to which the brake  36  is applied. The cylinder  33   b  serves as a brake drum. The balls  35  are support members for supporting the internal gear  33 . 
     As shown in FIG. 4, the brake  36  of the main clutch  30  includes an anchor pin  41  mounted to the clutch case  34 , a pair of brake shoes  42 ,  42  supported by the anchor pin  41 , a working cam  43  for expanding the brake shoes  42 ,  42 , a lever  44  coupled to the working cam  43 , and a cable  46  coupled to the lever  44  via an extension spring  45 . 
     The brake shoes  42 ,  42  are provided with return springs  47 ,  47  resiliently pulling them toward one another and brake pads  48 ,  48  to lock the internal gear  33 . The cable  46  is coupled to the clutch lever  13  (See FIG.  1 ). 
     Now the function of the main clutch  30  will be described with reference to FIG.  3 . 
     In the state shown in FIG. 3, the brake  36  is released and the internal gear  33  is rotatable. When the sun gear  31  is rotated with the output shaft  21  of the engine  20 , the planet gears  37  are rotated. At this time, the internal gear  33 , being in a free state, rotates. As a result, the planet frame  38  is not rotated. The main clutch  30  thus maintains a so-called clutch-off state in which no power of the engine  20  is transmitted from the output shaft  21  to the input shaft  51  of the transmission  50 . 
     Thereafter, when the clutch lever  13  (See FIG. 1) is operated to pull the cable  46 , the brake  36  is turned on. The internal gear  33  is prevented from rotating. When the sun gear  31  is rotated, the planet gears  37  are rotated. At this time, the internal gear  33 , being in a locked state, is not rotated. As a result, the planet frame  38  is rotated. The main clutch  30  is thus switched to a so-called clutch-on state in which the power of the engine  20  is transmitted from the output shaft  21  to the input shaft  51  of the transmission  50 . When the clutch lever  13  is released, the main clutch  30  is automatically returned to the former clutch-off state. 
     Here the reference is once returned to FIG. 2 to continue the description. The input shaft  51  of the transmission  50  is concentric with the output shaft  21  of the engine  20 . A driving bevel gear  52  provided at the lower end of the input shaft  51  is engaged with a first driven bevel gear  54  provided on the rotary countershaft  53  to transmit power from the input shaft  51  to the rotary countershaft  53 . 
     The transmission  50  has the rotary countershaft  53 , a first countershaft  55 , a second countershaft  56  and an axle  57  horizontally arranged across the body width from the front to the rear in this order. The shafts and axle  53 ,  55 ,  56  and  57  are coupled to one another with gear mechanisms. The transmission case  58  of the transmission  50  can thus be made longitudinally longer and transversely narrower (across the two sides of the figure sheet). The transmission case  58  can also be smaller in height (thinner). 
     A bottom surface  58   a  of the transmission case  58  is flat and substantially parallel with the ground. More specifically, with a center line Pe of the output shaft  21  of the engine  20  as a vertical line, the bottom surface  58   a  is made substantially parallel with a horizontal line Ho perpendicular to the vertical line Pe. The horizontal line Ho is parallel with the ground. 
     A front portion of the bottom surface  58   a  of the transmission case  58  is sloped rearward. The inclination angle θ1 of the bottom surface  58   a  with respect to the horizontal line Ho is a very small angle of about 5 degrees. 
     The cultivator  10  has a transmission shaft  71  coupling the rotary countershaft  53  to the rotary working unit  120  (See FIG.  1 ). The transmission shaft  71  is covered by a tubular case  73  attached to the transmission case  58 . 
     More specifically, a first driven bevel gear  54  provided on the rotary countershaft  53  is engaged with a second driven bevel gear  72  provided on the transmission shaft  71  which is extended forwardly and downwardly toward a rotor shaft  100 . The transmission shaft  71  is rotatably supported on bearings  74  and  75  to the tubular case  73 , and the proximal end of the tubular case  73  is bolted to a mounting eye  58   b  of the transmission case  58 . With respect to the center line Pe of the output shaft  21 , the inclination angle θ2 of the transmission shaft  71  and the tubular case  73  is about 60 degrees. 
     Since the thin transmission case  58  is used as described above, the height from the rotor shaft  100  to the bottom surface  58   a  of the transmission case  58  is relatively larger. The height of the bottom surface  58   a  from the ground is thus increased as compared with that of a conventional one. 
     The tubular case  73  consists of a cylinder and is provided with a housing case  94  integrally formed at its front end. The housing case  94  is a split case demountable relative to the center of the rotor shaft  100 . 
     As will be clear from the above description, arranging the vertical engine  20  between the rear axle  57  and the front rotor shaft  100  to shift the center of gravity of the cultivator  10  forward enables applying part of the weight of the engine  20  to the rotary working unit  120  (See FIG.  1 ). 
     The output shaft  21  of the engine  20  is vertically arranged concentrically with the input shaft  51  of the transmission  50 . In a conventional cultivator, a horizontal engine with an output shaft laterally protruded is used and a belt runs between the output shaft of the engine and an input shaft of a transmission. In the present invention, the engine  20  can be made close to the upper surface of the transmission case  58 . Thus reducing the height of the engine  20  enables lowering the center of gravity of the cultivator  10 . 
     FIG. 5 is a cross-sectional view taken along line  5 — 5  in FIG. 2, showing in section part of the transmission case  58 . 
     A first driving spur gear  61  and a second driving spur gear  62  are provided on the rotary countershaft  53 . A first driven spur gear  63 , a second driven spur gear  64  and a dog clutch  65  are provided on the first countershaft  55 . The dog clutch  65  is switched to enable switching between release of power transmission from the rotary countershaft  53  to the axle  57  via the first countershaft  55  and high-speed or low-speed power transmission from the rotary countershaft  53  to the axle  57  via the first countershaft  55 . In the figure, reference numeral  67  denotes a selector lever. 
     FIG. 5 shows that the transmission case  58  is longitudinally long and transversely narrow. The narrow width of the transmission case  58  allows the driving wheels  11  shown in imaginary lines to be made close to the center CL of the body width or be distanced outwardly from the center CL of the body width. 
     FIG. 6 is a cross-sectional view taken along line  6 — 6  in FIG. 2, showing in section a cultivation power transmission mechanism  80  for transferring power from the transmission to the rotor shaft  100 , and the surroundings. The rotor shaft  100  extends horizontally across the body width and includes a main rotor shaft  84 , a left hollow shaft  85  and a right hollow shaft  87 . 
     The cultivation power transmission mechanism  80  includes the transmission shaft  71  for transmitting the power of the engine  20  (See FIG. 2) to the rotor shaft  100 , a first bevel gear  81  provided at the distal end of the transmission shaft  71 , a second bevel gear  82  and a third bevel gear  83  arranged in parallel with one another, each engaging the first bevel gear  81 , the main rotor shaft  84  integrally provided to the second bevel gear  82 , the left hollow shaft  85  relatively rotatably fitted onto the main rotor shaft  84  and integrally provided to the third bevel gear  83 , a left gear  86  provided to the left hollow shaft  85  in addition to the third bevel gear  83 , the right hollow shaft  87  relatively rotatably fitted onto the main rotor shaft  84  in such a manner as sandwiching the second and third bevel gears  82  and  83  with the left gear  86 , a right gear  88  provided to the right hollow shaft  87 , a countershaft  93  with gears (a counter left gear  91  and a counter right gear  92 ) spanning across the left and right gears  86  and  88  so as to mechanically couple the right gear  88  to the left gear  86 , and the housing case  94  housing in a lump at least the transmission shaft  71 , the first, second and third bevel gears  81 ,  82  and  83 , the left and right gears  86  and  88 , and the countershaft  93 . 
     The main rotor shaft  84  is a long solid shaft extending across the body width, with a reverse-rotating left sleeve  95  and a reverse-rotating right sleeve  96  demountably mounted to its left and right ends by bolting or the like. The left hollow shaft  85  is integrally mounted at its left end a forward-rotating left sleeve  97  by keying or the like. The right hollow shaft  87  is integrally mounted at its right end a forward-rotating right sleeve  98  by keying or the like. These sleeves  95  to  98  are hollow shafts. In the figure, reference numerals  111  to  113  denote bearings and  114  a thrust bearing. 
     FIG. 7 is a front view of the front-rotary cultivator according to the present invention, showing that the engine  20 , the clutch case  34 , the transmission case  58 , and the tubular case  73  are arranged along the center CL of the body width, and the clutch case  34  and the transmission case  58  are fallen within the body width W 1  of the engine  20 . 
     The rotary working unit  120  is an assembly of a plurality of tillage tines. The tillage tines consist of a plurality of forward-rotating tines  121  and  122  (that is, a plurality of first forward-rotating tines  121  and a plurality of second forward-rotating tines  122 ) and a plurality of reverse-rotating tines  123 . The words “tillage tines” are hereinafter used as words collectively meaning the first forward-rotating tines  121 , the second forward-rotating tines  122  and the reverse-rotating tines  123 . The words “forward-rotating tines  121  and  122 ” include the first forward-rotating tines  121  and the second forward-rotating tines  122 . 
     The present invention is first characterized in that the forward-rotating tines  121  and  122  of the tillage tines are arranged in the transverse center of the transmission case  58  as the cultivator body, and the reverse-rotating tines  123  are arranged transversely outward of the forward-rotating tines  121  and  122 . 
     More specifically, the rotary working unit  120  has four rows arranged in the transverse direction of the cultivator body, consisting of: {circle around (1)} a group  131  of the forward-rotating tines  121  and  122  attached to a mounting plate  97   a  of the forward-rotating left sleeve  97  left inside (first tine group  131 ); {circle around (2)} a group  132  of the forward-rotating tines  121  and  122  attached to a mounting plate  98   a  of the forward-rotating right sleeve  98  right inside (second tine group  132 ); {circle around (3)} a group  133  of the reverse-rotating tines  123  attached to a mounting plate  95   a  of the reverse-rotating left sleeve  95  left outside (third tine group  133 ); and {circle around (4)} a group  134  of the reverse-rotating tines  123  attached to a mounting plate  96   a  of the reverse-rotating right sleeve  96  right outside (fourth tine group  134 ). 
     The left and right driving wheels  11 ,  11  are arranged rearward of the reverse-rotating tines  123 . Specifically, the left driving wheel  11  is arranged rearward of the third tine group  133  and the right driving wheel  11  is arranged rearward of the fourth tine group  134 . 
     As will be clear from the above description, a vertical engine is used as the engine  20  and the output shaft  21  (See FIG. 2) is arranged in the center CL of the body width so as to increase the weight balance in the transverse direction of the cultivator  10 . Since the engine  20  is located in the center CL of the width, the left and right driving wheels  11 ,  11  can be arranged close to the engine  20  in a sandwiching manner to make the driving wheels  11 ,  11  close to the center CL of the body width. 
     FIGS. 8A and 8B are structural diagrams of the rotary working unit according to the present invention; FIG. 8A is an exploded view of the tillage tines constituting the rotary working unit  120 ; and FIG. 8B is a view taken from the direction of an arrow  8 B in FIG.  8 A. For ease of understanding, the mounting plates  95   a ,  96   a ,  97   a  and  98   a  and the rotor shaft  100  shown in FIGS. 6 and 7 are omitted. 
     The forward-rotating tines  121  and  122  rotate from the upper front of a traveling direction Ru of the cultivator  10  (See FIG. 7) toward the ground in a direction R 1 , that is, the forward-rotating direction R 1 . The reverse-rotating tines  123  rotate from the upper rear of the traveling direction Ru toward the ground in a direction R 2 , that is, the reverse-rotating direction R 2 . 
     The rotary working unit  120  is characterized in that the forward-rotating tines  121  and  122  are arranged in the same phase in a side view and the reverse-rotating tines  123  are arranged in the same phase in a side view. This will be described in detail below. 
     Each of the first and second tine groups  131  and  132  has the four forward-rotating tines  121  and  122  lapped at their proximal ends to one another to form generally parallel cross-shaped structures or crosses with reference to the center Pf of the rotor shaft. Each of the third and fourth tine groups  133  and  134  has the four reverse-rotating tines  123  lapped at their proximal ends to one another to form generally parallel cross-shaped structures or crosses with reference to the center Pf of the rotor shaft. 
     In FIG. 8A, the first tine group  131  consists of the combination of: {circle around (1)} the first forward-rotating tine  121  extending in the traveling direction Ru (i.e., forward and upward) of the cultivator  10 ; {circle around (2)} the second forward-rotating tine  122  extending rearward and upward; {circle around (3)} the first forward-rotating tine  121  extending rearward and downward; and {circle around (4)} the second forward-rotating tine  122  extending forward and downward. The two first forward-rotating tines  121 ,  121  are shaped like a hatchet, being curved at their distal ends toward the second tine group  132  and also in the reverse-rotating direction R 2 . The two second forward-rotating tines  122 ,  122  are shaped like a hatchet, being curved at their distal ends toward the third tine group  133  and also in the reverse-rotating direction R 2 . 
     The second tine group  132  is formed symmetrically with the first tine group  131  and is arranged in the same phase with the first tine group  131 . 
     The third tine group  133  is arranged with its phase shifted at about 45 degrees in the forward-rotating direction R 1  with respect to the first tine group  131 , consisting of the four reverse-rotating tines  123  extending forward, rearward, upward and downward. All the reverse-rotating tines  123  are shaped like a hatchet, being curved at their distal ends toward the first tine group  131  and also in the forward-rotating direction R 1 . 
     The fourth tine group  134  is formed symmetrically with the third tine group  133  and is arranged in the same phase with the third tine group  133 . 
     As a matter of fact, the phases of the respective tine groups  131  to  134  are varied with the rotation of the rotor shaft  100  (See FIG.  6 ). 
     Now, the function of the cultivation power transmission mechanism  80  of the above configuration will be described with reference to FIGS. 2,  7  and  9  to  11 . 
     In FIG. 2, the power of the engine  20  is transmitted from the output shaft  21 , via the main clutch  30 , the input shaft  51  of the transmission  50 , the driving bevel gear  52 , the first driven bevel gear  54  and the second driven bevel gear  72 , to the transmission shaft  71 . 
     In FIG. 9, when the transmission shaft  71  is rotated in a rotation direction R 0  by the engine, the power of the engine is transmitted from the transmission shaft  71 , via the first bevel gear  81 , the second bevel gear  82  and the main rotor shaft  84 , to the reverse-rotating left sleeve  95  and the reverse-rotating right sleeve  96 . As a result, the reverse-rotating left and right sleeves  95  and  96  rotate in the reverse-rotating direction R 2 . 
     In FIG. 10, when the transmission shaft  71  is rotated in the rotation direction R 0  by the engine, the power of the engine is also transmitted from the transmission shaft  71 , via the first bevel gear  81 , the third bevel gear  83  and the left hollow shaft  85 , to the forward-rotating left sleeve  97 . As a result, the forward-rotating left sleeve  97  rotates in the forward-rotating direction R 1 . 
     In FIG. 11, when the transmission shaft  71  is rotated in the rotation direction R 0  by the engine, the power of the engine is also transmitted from the transmission shaft  71 , via the first bevel gear  81 , the third bevel gear  83 , the left hollow shaft  85 , the left gear  86 , the counter left gear  91 , the countershaft  93 , the counter right gear  92 , the right gear  88  and the right hollow shaft  87 , to the forward-rotating right sleeve  98 . As a result, the forward-rotating right sleeve  98  rotates in the forward-rotating direction R 1 . 
     Therefore, as shown in FIG. 7, the power of the engine  20  can be transmitted to rotate the reverse-rotating tines  123  attached to the reverse-rotating left and right sleeves  95  and  96  (the main rotor shaft  84  in FIG. 6) and the forward-rotating tines  121  and  122  attached to the forward-rotating left and right sleeves  97  and  98  (left and right hollow shafts  85  and  87  in FIG. 6) in opposite directions for cultivating operation. 
     As shown in FIG. 12, the rotary working unit  120  in this embodiment is characterized in that the forward-rotating tines  121  and  122  of the tillage tines are arranged in the center of the body width and the reverse-rotating tines  123  are arranged transversely outward of the forward-rotating tines  121  and  122 . 
     The forward-rotating tines  121  and  122  can be (forwardly) rotated in the forward-rotating direction R 1  from the upper front of the traveling direction toward the ground Gr 1 . The reverse-rotating tines  123  can be (reversely) rotated in the reverse-rotating direction R 2  from the upper rear of the traveling direction toward the ground Gr 1 . 
     The forward-rotating tines  121  and  122  and the reverse-rotating tines  123  during cultivation produce the cultivation reaction force. The direction of the cultivation reaction forces against the forward-rotating tines  121  and  122  is forward and upward of the traveling direction of the cultivator  10 , that is, opposite to the rotation direction R 1  of the forward-rotating tines  121  and  122 . The direction of the cultivation reaction forces against the reverse-rotating tines  123  is rearward of the traveling direction of the cultivator  10 , that is, opposite to the rotation direction R 2  of the reverse-rotating tines  123 . The cultivation reaction forces against the forward-rotating tines  121  and  122  and the cultivation reaction forces against the reverse-rotating tines  123  thus work in opposite directions. 
     If all the tillage tines are the forward-rotating tines  121  and  122 , the cultivation reaction force is greater, making it difficult to prevent the occurrence of a dashing phenomenon due to the cultivation reaction force. According to the present embodiment, the cultivation reaction force arising from cultivation with the forward-rotating tines  121  and  122  can be cancelled to some extent by the cultivation reaction force arising from cultivation with the reverse-rotating tines  123 . As a result, the occurrence of the dashing phenomenon due to the cultivation reaction force can be further prevented. 
     The rotary working unit  120  in this embodiment is further characterized in that the forward-rotating tines  121  and  122  are arranged in the same phase in a side view and the reverse-rotating tines  123  are arranged in the same phase in a side view. 
     With the cultivator  10  propelled, the forward-rotating tines  121  and  122  in the center of the body width can be forwardly rotated to simultaneously dig into the ground Grl for cultivation, thereby digging out the cultivated soil rearward of the cultivator body. 
     The reverse-rotating tines  123  arranged transversely outward of the forward-rotating tines  121  and  122  can be reversely rotated simultaneously with the rotation of the forward-rotating tines  121  and  122  to simultaneously dig into the ground Gr 1 , thereby digging out the cultivated soil forward of the cultivator body. 
     The simultaneous digging of the forward-rotating tines  121  and  122  into the ground Gr 1  can increase the degree of digging as compared with differential digging. The simultaneous digging of the reverse-rotating tines  123  into the ground Gr 1  can also increase the degree of digging. This results in an increase in the depth of plowing with the forward-rotating tines  121  and  122  and the reverse-rotating tines  123 , further increasing cultivation performance. 
     Further, simultaneous digging of the forward-rotating tines  121  and  122  into the ground Gr 1  can make the cultivation reaction forces against the forward-rotating tines  121  and  122  approximately equal. The same applies to the reverse-rotating tines  123 . The approximately equal cultivation reaction forces allow further prevention of the unbalanced occurrence of a dashing phenomenon and also allow prevention of the occurrence of a pitching phenomenon (phenomenon in which the cultivator  10  swings back and forth like a seesaw). 
     The simultaneous digging of the forward-rotating tines  121  and  122  into the ground Gr 1  with the simultaneous digging of the reverse-rotating tines  123  into the ground Gr 1  can make approximately equal the left and right cultivation reaction forces acting on the cultivator  10 . This also enables preventing the occurrence of a rolling phenomenon (phenomenon in which the cultivator  10  rolls around the longitudinal axis passing through the center of gravity of the cultivator  10 ). This can further prevent the snaking of the cultivator  10 , increasing linearity in travel and steerage, further increasing the workability, and also improving cultivation finish. 
     Further, it is needless for the cultivator  10  of a light weight to increase the weight distribution to the tillage tines by disposing the engine or a heavy load such as a counterweight in front of or above the tillage tines so as to increase the degree of digging of the tillage tines to prevent a dashing phenomenon. In the operation of pushing down the operating handle  12  (See FIG. 1) to lift the tillage tines to turn the cultivator  10 , the pushing-down force is not thus increased. This can reduce the workload of the operator, increasing steerage. 
     In general, when the driving wheels  11 ,  11  are arranged transversely outward of the rotary working unit  120  (tillage tines), the driving wheels  11 ,  11  pass over the uncultivated rough and hard ground Gr 1 . In this situation, the position of the cultivator  10  can largely vary, providing unstable cultivation. Further, since the tillage tines dig into the ground Gr 1 , the cultivator  10  leans forward. 
     When the driving wheels  11 ,  11  are arranged rearward of the forward-rotating tines  121  and  122 , that is, rearward of the first and second tine groups  131  and  132 , soil cultivated by the forward-rotating tines  121  and  122  is broken up rearward of the cultivator body and the driving wheels  11 ,  11  run over the ground Gr 2  broken up and mounded. This makes the cultivator  10  lean forward. 
     With the rotary working unit  120  of this embodiment, the driving wheels  11 ,  11  are arranged rearward of the reverse-rotating tines  123  to dig out the cultivated soil forward of the cultivator body, that is, rearward of the third and fourth tine groups  133  and  134 . The driving wheels  11 ,  11  can run over the ground Gr 3  dug down by the reverse-rotating tines  123 . This can increase the degree of settling of the driving wheels  11 ,  11  to maintain the cultivator  10  horizontally. Stable cultivation can thus be provided. Since the engine also has a horizontal position, the oil surface of a lubricant in the engine is not slanted. Thus smooth lubrication of the engine can be provided. 
     FIG. 13 illustrates the cultivator in this embodiment with the operating handle  12  placed on the ground Gr 1 . 
     The center of gravity G 1  of the entire cultivator  10  is located slightly closer to the operating handle  12  than a vertical line V 1  passing through the axle  57  when the operating handle  12  is placed on the ground Gr 1  with rearward inclination. Placing the operating handle  12  on the ground Gr 1  can thus maintain the rotary working unit  120  in a lifted state. With this lifted state, the rotary working unit  120  stationary or rotated can be cleaned, facilitating a cleaning operation. 
     Further, the engine  20  is, as shown in FIG. 1, a vertical engine with the cylinder  22  extended substantially horizontally forward. When the engine  20  is leaned rearward as shown in FIG.  13 , the cylinder  22  is thus raised. The rearward leaning of the cultivator  10  will thus not cause the lubricant to enter the cylinder  22 . 
     A modification of the rotary working unit  120  will be described with reference to FIGS. 14A,  14 B,  14 C and  15 . Components identical to those in the rotary working unit  120  shown in FIGS. 7,  8  and  12  are attached the same reference numerals and will not be described. 
     In a rotary working unit  120  with the modification shown in FIG. 14A, only a plurality of reverse-rotating tines  123  are arranged in the same phase in a side view. This will be described in detail below. 
     A second tine group  132  is formed symmetrically with a first tine group  131  and is arranged with its phase shifted about 45 degrees toward a forward-rotating direction R 1  relative to the first tine group  131 . A third tine group  133  is, as shown in FIG. 14B, arranged with its phase shifted about 22.5 degrees toward the forward-rotating direction R 1  relative to the first tine group  131 . A fourth tine group  134  is formed symmetrically with the third tine group  133  and is arranged in the same phase with the third tine group  133 . 
     In the rotary working unit  120  of this modification, the forward-rotating tines  121  and  122  are thus shifted in phase about 45 degrees from one another in a side view and the reverse-rotating tines  123  are arranged in the same phase in a side view. 
     As a matter of fact, the phases of the tine groups  131  to  134  vary with the rotation of a rotor shaft  100  (See FIG.  6 ). 
     As shown in FIG. 15, in a front-rotary cultivator  10  using the rotary working unit  120  of the modification, the forward-rotating tines  121  and  122  and the reverse-rotating tines  123  produce, during cultivation, cultivation reaction forces. The direction of the cultivation reaction forces against the forward-rotating tines  121  and  122  is forward and upward of the traveling direction of the cultivator  10 , that is, opposite to a rotation direction R 1  of the forward-rotating tines  121  and  122 . The direction of the cultivation reaction forces against the reverse-rotating tines  123  is rearward of the traveling direction of the cultivator  10 , that is, opposite to a rotation direction R 2  of the reverse-rotating tines  123 . The cultivation reaction forces against the forward-rotating tines  121  and  122  and the cultivation reaction forces against the reverse-rotating tines  123  thus act in opposite directions. 
     According to this modification, the cultivation reaction forces arising from cultivation with the forward-rotating tines  121  and  122  can be cancelled to some extent by the cultivation reaction forces arising from cultivation with the reverse-rotating tines  123 . This results in further prevention of occurrence of a dashing phenomenon due to the cultivation reaction forces. 
     Further, with the cultivator  10  propelled, the forward-rotating tines  121  and  122  located in the center of the body width can forwardly rotate to dig into the ground Gr 1  for cultivation, digging out the cultivated soil rearward of the cultivator body. 
     Furthermore, the reverse-rotating tines  123  arranged transversely outward of the forward-rotating tines  121  and  122  can reversely rotate simultaneously with the rotation of forward-rotating tines  121  and  122  to simultaneously dig into the ground Gr 1 , digging out the cultivated soil forward of the cultivator body. 
     The simultaneous digging of the reverse-rotating tines  123  into the ground Gr 1  can increase the degree of digging as compared with differential digging. This results in an increase in the depth of plowing with the reverse-rotating tines  123 , further increasing cultivation performance. 
     The simultaneous digging of the reverse-rotating tines  123  into the ground Gr 1  can also make the reaction forces against the reverse-rotating tines  123  approximately equal to one another. The approximately equal cultivation reaction forces can prevent the unbalanced occurrence of a dashing phenomenon and can also prevent the occurrence of a pitching phenomenon (phenomenon in which the cultivator  10  swings back and forth like a seesaw). This can thus prevent the snaking of the cultivator  10 , increasing its linearity in travel, steerage and workability, and also improving cultivation finish. 
     The present disclosure relates to the subject matter of Japanese Patent Application No. 2002-008013, filed Jan. 16, 2002, and the subject matter of Japanese Patent Application No. 2002-311020, filed October 25, the disclosures of which are expressly incorporated herein by reference in their entireties.