BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cultivating apparatus in which a rear cover for covering the rear side of a cultivating section is urged in a direction of contact with the ground by-means of a pressing device having a biasing element such for example as a gas or a spring.
2. Description of the Related Art
There has hitherto been proposed a cultivating apparatus roughly composed of a machine frame, a cultivating section disposed below the machine frame, a rear cover for covering the rear side of the cultivating section, and a gas spring formed so as to extend across the machine frame side and the rear-cover side of the apparatus. In the cultivating section, a multiplicity of cultivating tines are attached to a tine shaft having an axis aligned with a direction of from right to left of the apparatus (hereafter also referred to as "horizontal direction") . As the tine shaft is driven to rotate about the horizontal axis, the cultivating tines effect soil cultivation. The rear cover is so shaped as to be inclined downwardly from front to rear of the apparatus when set in a working position for leveling off the soil cultivated by the cultivating section, and the anterior top side thereof is supported on the machine

frame side of the apparatus for free running movement about a horizontal axis, whereby the rear cover is free to rock up and down. The gas spring serves as a pressing device for urging the rear cover in a downward direction to cause the rear lower end side of the rear cover in the working position to get down to the ground (refer to Japanese Unexamined Patent Publication JP-A 2007-151503).
The gas spring is so shaped as to be inclined downwardly from front to rear of the apparatus under the condition where the rear cover assumes the working position. Moreover, in the gas spring, a piston rod is disposed so as to protrude from a tube obliquely downwardly in a rearward direction in an advance able and retractable manner. An attachment portion of the gas spring located on the bottom side of the tube is, in a position forward of and above a turning fulcrum of the rear cover, pivotally coupled to machine frame-side bracket disposed on the machine frame side of the apparatus. On the other hand, an attachment portion of the gas spring located on the front end side of the piston rod is pivotally coupled to a rear cover-side bracket disposed on the rear cover. A pivotal point of the gas spring and one of the attachment portions of the gas spring that lies on the same side as the pivotal point does take up the same position with respect to the direction of the length of the gas spring (a pivotal point located toward one-end of the gas spring coincides with one of the attachment portions of the gas spring

that lies on the same side as the said pivotal point does, with respect to the direction of the length of the gas spring, and a pivotal point located toward the other end of the gas spring coincides with the other attachment portion of the gas spring that lies on the same side as the said pivotal point does, with respect to the direction of the length of the gas spring).
Moreover, the piston rod of the gas spring is designed to advance from and retract into the tube as the rear cover is moved up and down.
In the conventional cultivating apparatus thus far described, however, as the rear cover is lifted up, the piston rod is brought into a contracted state. Therefore, if the uppermost position of the rear cover is set unduly high, the piston may abut against the bottom-side end of the interior of the tube when the rear cover assumes the uppermost position. SUMMARY OF TEE INVENTION
The present invention has been devised in view of the foregoing problem, and accordingly its object is to provide a cultivating apparatus in which an uppermost position of a rear cover can be set at a higher level.
By way of the implementation of a technical measure taken by the present invention to solve the foregoing technical problem, there is provided a cultivating apparatus composed of: a machine fram.e 2; a cultivating section 3 disposed below a main cover 19 attached to the machine frame 2; a rear cover 20 for covering

the rear part of the cultivating section 5, the anterior end side of which is supported on the rear end side of the main cover
19 for free turning movement about a horizontal axis to render the rear cover 20 freely rock able up and down; and a long pressing device 27 having a biasing element for urging the rear cover
20 in a downward direction, which is pivotally supported on a bracket 30 disposed in a machine frame 2 side region and a bracket 31 disposed in a rear-cover side region to enable the rear cover 20 to rock upwardly against a biasing force exerted by the biasing element.
In this construction, one side of the pressing device 27 is pivotally supported on the same-side bracket 30 in such a manner that a biasing force-receiving portion at one side of the pressing device 27 is located outwardly relative to a same-side pivotal point X of the pressing device 27 with respect to a direction longitudinally of the pressing device 27.
By way of the implementation of another technical measure, there is provided a cultivating apparatus composed of: a machine frame 2; a cultivating section 3 disposed below a main cover 19 attached to the machine frame 2; a rear cover 20 for covering the rear part of the cultivating section 3, the anterior end side of which is supported on the rear end side of the main cover 19 for free turning movement about a horizontal axis to render the rear cover 20 freely rock able up and down; and a long pressing device 27 having a biasing element for urging the rear cover

20 in a downward direction, which is pivotally
racket 30 disposed in a machine frame 2 side region and a bracket 31 disposed in a rear-cover side region to enable the rear cover 2 0 to rock upwardly against a biasing force exerted by the biasing element.
In this construction, at least an attachment portion 51, 108 at lengthwise one side of the pressing device 27 is fitted with one end side of a link 65, and the other end side of the link 65 is pivotally supported on the bracket 30, which lies on the same side as the attachment portion (51, 108) to which is attached one end side of the link 65 does, in a position located inwardly relative to the attachment portion 51 to which is attached one end side of the link 65 with respect to a direction longitudinally of the pressing device 27.
Moreover, lengthwise one side of the pressing device 27 may be supported via the link 65 on the machine frame 2-side bracket 30.
Moreover, lengthwise one side of the pressing device 27 may be supported via the link 65 on the rear cover 20-side bracket 31.
Moreover, it is preferable to provide a biasing force changing member 57 for allowing selection between a biased condition where the biasing force produced by the biasing element of the pressing device 27 sets upon the rear cover 20 and a freed condition where the biasing force produced by the biasing element

no longer sets upon the rear cover 20.
Moreover, the pressing device 27 may be built as a gas spring.
Moreover, the biasing element may be a coil spring 107.
According to the present invention, one side of the pressing device is pivotally supported on the same-side bracket in such a manner that the biasing force-receiving portion at one side of the pressing device is located outwardly relative to the same-side pivotal point of the pressing device with respect to the direction longitudinally of the pressing device (the biasing force-receiving portion at one side of the pressing device is located outwardly away from the same-side pivotal point of the pressing device with respect to the direction longitudinally of the pressing device) . With this arrangement, the uppermost position of the rear cover can be set at a higher level.
Moreover, let it be assumed that a cultivating apparatus employing the conventional pressing device and the cultivating apparatus according to the present invention are identical in terms of the level of the uppermost position of the rear cover. In this case, in the cultivating apparatus employing the conventional pressing device in which the pivotal point is set inthepreviously-describedmanner, when the rear cover is lowered significantly, an intermediate part of the pressing device may abut against the vicinity of the pivoted portion of the rear cover, which gives rise to a problem such as the impossibility

of lowering the rear cover ^o = large extern: or the risk of deformation of the pivoted portion of the rear cover because of the abutment of the intermediate part of the pressing device against the vicinity of the pivoted portion of the rear cover. On the other hand, in the cultivating apparatus of the present invention, by virtue of the foretasted structure, the advantages are gained that the rear cover can be lowered to a larger extent than in the conventional construction and the pivoted portion of the rear cover can be protected from deformation caused by the abutment of the intermediate part of the pressing device against the vicinity of the pivoted portion of the rear cover when the rear cover assumes the lowermost position. BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a side view of a means for actuating a rear cover;
Fig. 2 is a side view of a cultivating apparatus;
Fig. 3 is a side view of a part for attachment of a gas spring;
Fig. 4 is a schematic plan view of the means for actuating the rear cover;
Fig. 5 is a plan sectional view of the part for attachment of the gas spring;
Fig. 6 is a partly sectional view of a side face of a resiliently lowering device;
Fig. 7 is a side view showing a state where up-and-down-rocking motions are imparted to the rear cover in the presence

of a biasing force exerted by the gas spring;
Fig. 8 is a side view showing a state where up-and-down rocking motions are imparted to the rear cover in the absence of the biasing force exerted by the gas spring;
Fig. 9 is a schematic side view of the means for actuating the rear cover employing the gas spring in accordance with another embodiment of the present invention;
Fig. 10 is a schematic plan view; of the means for actuating the rear cover employing the gas spring according to another embodiment;
Figs. 11 are sectional views of a portion for supporting a tube of the gas spring of the means for actuating the rear cover according to another embodiment, with (a) showing the plane section thereof, (b) showing the side-face section thereof, and (c) showing the back-face section thereof;
Fig. 12 is a schematic side view of the means for actuating the rear cover employing the gas spring in accordance with still another embodiment of the present invention;
Fig. 13 is a partly sectional plan view of the means for actuating the rear cover employing the gas spring according to still another embodiment;
Fig. 14 is a side view showing a state where up-and-down rocking motions are imparted to the rear cover in the presence of a biasing force exerted by the gas spring of the means for actuating the rear cover according to still another embodiment;

Fig. 15 is a schematic side view of a comparative example of the means for actuating the rear cover employing the gas spring;
Fig. 16 is a side view of a modified example of a mechanism for actuating the rear cover by means of the gas spring;
Figs. 17 are views of the modified example, with (a) showing the plane section of the tube-side pivoted portion of the gas spring, and (b) showing the back-face section thereof;
Fig. 18 is a schematic side view showing an adoption example of a pressing device employing a coil spring as a biasing element; and
Fig. 19 is partly sectional plan view showing the adoption example of the pressing device employing the coil spring as the biasing element. DETAILED DESCRIPTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
In Fig. 2, reference numeral 1 represents a cultivating apparatus that carries out cultivation while moving around agricultural fields, which is detachably attached via a hitch such as a three-point link mechanism to the rear side of a vehicle such as a tractor for free up-and-down movement.
The cultivating apparatus 1 is mainly composed of a machine frame 2 which is coupled to the three-point link mechanism, a cultivating section 3 disposed below the machine frame 2, and a tiller cover 4 for covering the cultivating section 3.

In the machine frame 2, support arms to protrude rightward and leftward, respectively, from a gear case 5 located centrally in a direction of from right to left of the apparatus (hereafter also referred to as "horizontal direction") . The outer end side of the left-hand support arm 6 is fitted with the upper part of a power transmission case 7, whereas the outer end side of the right-hand support arm 6 is fitted with the upper part of a non-illustrated side frame. That is, the machine frame 2 is fashioned as a portal-shaped construction as viewed from the back.
A top mast 8 protrudes upwardly from the gear case 5 of the machine frame 2, and the lower part of the top mast 8 is secured to the right-hand and left-hand sides of the gear case 5. The top mast 8 is provided with an upper bracket 9 extending obliquely upwardly in a frontward direction. On the upper end side of the upper bracket 9 is disposed an upper coupling pin 10 with which is engaged, from below, an engagement portion of the upper part of a coupling frame disposed on the rear end side of the three-point link mechanism. A lower bracket 11 is secured to each of the right-hand and left-hand support arms 6. The lower brackets 11 are each provided with a lower coupling pin 12 to which is coupled a hitch of the lower part of the coupling frame.
Note that the upper coupling pin 10 miay be directly coupled to an operating machine-side coupling portion of a top link of

the three-point link mechanism, and the lovjer coupling pin 12 may be directly coupled to an operating machine-side coupling portion of a lower link of the three-point link mechanism.
Moreover, the lower link is coupled via a lift' rod to a
lift arm which is moved up and down by a hydraulic power unit
disposed at the rear of the tractor. By operating the hydraulic
power unit in a manner to rock the lower link up and down, the
cultivating apparatus 1 can be lifted and lowered ■ //' ,
correspondingly. ij
The hydraulic power unit is constructed of a single-action type hydraulic cylinder. The cultivating apparatus 1 is lifted under a hydraulic pressure, and is lowered under its own weight.
Moreover, on the right-hand and left-hand lower brackets 11 is pivotally supported the anterior end side of a support frame 13 protruding rearwardly from the machine frame 2. The rear end side of the support frame 13 is fitted with a gauge wheel 14. Formed so as to extend from an intermediate part of the support frame 13 over the top mast 8 is a height adjustment device 15 for making adjustment to the height of the gauge wheel 14 by causing the support frame 13 to rock up and down.
The cultivating section 3 is composed of a tine shaft 16 constructed so as to extend between the lower parts of the power transmission case 7 and the side framte for free rotation about a horizontal axis, and a multiplicity of cultivating tines 17 attached to the tine shaft 16 along a horizontal direction.
11

The gear case 5 of i:he machine frarrie 2 is proviced wiuh a forwardly protruding PIC shaft 18 to which is transiriitted a power from a PTO shaft of the tractor via a power transmission shaft. The power inputted through the PIC shaft 18 to a power transmission systemdisposedwithin the gear case 5 is transmitted to the tine shaft 16 via a power transmission shaft disposed within the left-hand support arm 6 and a power transmission'system disposed within the power transmission case 7, where'i|5on the tine shaft 16 is driven to rotate in a direction indic/ated by an arrow A shown in Fig. 2.
The tiller cover 4 is composed of amain cover 19 for covering the upper part of the cultivating section 3, a rear cover 20 for covering the rear part of the cultivating section 3, and right-hand and left-hand side covers 21 for covering the right-hand lateral part and the left-hand lateral part, respectively, of the cultivating section 3.
The right-hand and left-hand side covers 21 are each composed of a front cover portion 22 for covering the upper lateral part of the cultivating section 3 and a rear cover portion 23 for covering a lateral region between the cultivating section 3 and the rear cover 20. The front cover portion 22 is divided into an upper segment and -a lower segment.
The upper segment of the front cover portion 22 is fixed relatively to the horizontally inner surfaces of the power transmission case 7 and the side frame. The lower segmient of
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the front cover portion 22 is fixed ro the upper segmeni; of zhe front cover portion 22.
The main cover 19 is disposed between the upper segments
of the front cover portions 22 and has its horizontally opposite
ends fixed to the corresponding upper segments of the front cover
portions 22. r
M
As shown in Figs. 1 and 2, the rear cover 20 is so'shaped as to be inclined downwardly from front to rear of the a^aratus when set in a working position where its lower rear end 1^ caused to get down to the ground of agricultural fields for leveling off the soil cultivated by the cultivating section 3 . A pivoted portion 24, which is located toward the anterior upper end of the rear cover 20, is pivotally supported on a turning fulcrum 25 supported on the rear end side of the main cover 19' for free rotation about a horizontal axis. That is, the rear cover 20 is supported for free up-and-down rocking motions on the m.ain cover 19 (the machine frame 2-side region) to allow the rear side thereof to move up and down..
The rear cover 20 maybe designed to have a freely detachable ground-leveling cover attached to the lower rear endside thereof.
In order to level off the soil which is prepared by the rear cover 20, the cultivating apparatus 1 of this embodiment has-, as a biasing means for urging the rear cover 20 in a direction of contact with the ground,'a resiliently lowering device 25 and a gas spring 27 illustrated as one examiple of the long pressing

device 27 that are shown in Figs. 1 ro S.
The resiliently lowering device 26 and che gas spring 27
are located above the rear cover 20 and arranged proximately
side by side in a horizontal direction. The resiliently lowering
device 2 6 and the gas spring 27 are so arranged as to be allocated
in each of a right-hand region and a left-hand region in rel-ation
J) to the center of the machine frame 2 in a horizontal diirection
(there are provided two paired biasing means, the biasii?^ means
',f in each pair consisting of a single resiliently lowering device
26 and a single gas spring 27).
In this embodiment, the gas'spring 27 is disposed horizontally outwardly of the resiliently lowering device 26 and is located below the resiliently lowering device 26.
As shown in Figs. 1 and 6, the resiliently lowering device 26 is composed of a resiliently lowering rod 28 formed of a pipe extending across the machine frame 2-side region and the rear cover 20-side region, and a coil spring 29 set surroundingly around the resiliently lowering rod 28 for actuating the rear cover 20.
The resiliently lowering rod 28 is disposed above the rear cover 20 so as to extend rearward under the condition where the rear cover 20 assumes the working position. The resiliently lowering rod 28 has its anterior end side pivotally supported on a bracket 30 formed uprightly on the rear end side of the upper surface of themain cover 19 (thebracket 30 will be referred
1 4

teas "machine frame-side bracket) and has its rear side inserted through a rod holder 32. The rod holder 32 is disposed in a bracket 31 formed uprightly on a midportion of the top surface (back surface) of the rear cover 20 in a front to rear direction, expressed differently, an anteroposterior direction (the bracket 31 will be referred to as "rear cover-side bracket).
Note that the machine frame-side bracket 30 may be secured to the support arm 5. That is, it is essential only that the machine frame-side bracket 30 be disposed in the machine frame 2 or a member fixed to the machine frame 2.
As shown in Fig. 5, the machine frame-side bracket 30 is composed of a right-hand side wall 30a, a left-hand side wall 30a, and a front wall 30b acting as the connection between the anterior ends of the right-hand and left-hand side walls 30a and is thus fashioned as a rearwardly opened, U-shaped member. In the upper part of the machine framie-side bracket 30 between the right-hand and left-hand side walls 30a is inserted the anterior end side of the resiliently lowering rod 28. The anterior end side of the resiliently lowering rod 28 is pivoted via a pivot shaft 33 to the right-hand and left-hand side walls 30a for free turning movement about a horizontal axis. In this way, the resiliently lowering rod 28 is allowed to rock about the pivot shaft 33 upwardly and downwardly.
As shown in Fig. 5, the rear cover-side bracket 31 is com.posed of a pair of right-hand and left-hand side plates 31a
15

thau are coupled to each other ar "their intermediate par~5 in a top to bottom direction, expressed differently, a vertical direction. In the upper part of the rear cover-side bracket 31 between the right-hand and left-hand side plates 31a is disposed the rod holder 32. The rod holder 32 is supported for free turning movement on the rear cover-side bracket 31, with a shaft portion 34 lying on the right-hand and left-hand sides thereof engaged for free rotation about a horizontal axis in a support hole 35 formed in the right-hand and left-hand side plates 31a.
Moreover, the rod holder 32 has an insertion hole 36 drilled all the way through from the front face to the rear face thereof in a direction perpendicular to the axis of the support hole 35 (shaft portion 34). The resiliently lowering rod 28 is inserted through this insertion hole 36. The rod holder 32 and the resiliently lowering rod 28 are freely shiftable relative to each other in a direction axially of the resiliently lowering rod 28.
The coil spring 29 is disposed forward of the rod holder 32, and a spring bearing member 37 is disposed forward of the coil spring 29. The spring bearing member 37 includes a key 39 engageable in a retention slot 38 formed on the surface of the resiliently lowering rod 28 , and a spring member 40 for urging the key 39 into engagement in the retention slot 38 . By engaging the key 3 9 in the retention slot 38, the spring bearing member
16

.
37 is positioned with respect to the resiliently 28.
Moreover, there are formed a multiplicity of the retention slots 38 that are spaced apart in the direction axially of the resiliently lowering rod 28. Further, as the spring bearing member 37 is driven to turn about the axis of the resiliently lowering rod 28, the key 39 can be detached from the retention slot 38 against a biasing force exerted by the spring m.ember 40 . After having been detached from the retention slot 3 8 against a biasing force exerted by the spring member 40, the key 39 is engaged in another retention slot 38, whereby making it possible to change the position of the spring bearing member 37 relative to the resiliently lowering rod 28 (the spring bearing member 37 is positionable in a plurality of locations along the direction axially of the resiliently lowering rod 28).
Then, with the rear cover 20 held in the working position, the coil spring 29 is brought into a compressed state between the spring bearing member 37 and the rod holder 32, whereupon a biasing force tending to move the rear cover 20 in a downward direction sets upon the rear cover 20. Moreover, by changing the position of the spring bearing member 37 while holding the coil spring 29 in compression between the spring bearing member 37 and the rod holder 32, it is possible to vary the biasing force exerted upon the rear cover 20.
Note that, by bringing about the engagement between the
1 /

spring bearing msin^cer 37 and the retention slor 3 8 located nearest the anterior end of the resiliently lowering device or by keeping the key 3 9 of the spring bearing member 37 out of engagemient withthe retention slot 38, it is possible to restrain the biasing force exerted by the coil spring 2 9 from setting upon the rear cover 20; that is, a freed condition is achieved.
Moreover, the resiliently lowering rod 28 has formed at its rear end an abutment 41 which controls the downward rocking motion of the rear cover 20 by making contact with the rear surface of the rod holder 32.
Further, the rod holder 32 is provided with a locking pin (not shown in the figure) and a changing lever 43. The locking pin restrains the relative movement between the rod holder 32 and the resiliently lowering rod 28 by being inserted into a locking hole 42 formed in the resiliently lowering rod 28. The changing lever 43 allows selection between a locking position where the locking pin is inserted into the locking hole 42 and a non-locking position where the locking pin is removed out of the locking hole 42.
The changing lever 43 is disposed at the top end of the rod holder 32 for free turning movement about a horizontal axis. As shown in Fig. 6, when the changing lever 43 is lowered to its down position, the locking pin is held in a position where it can be removed out of the locking hole 42 under the biasing force exerted by the spring . On the other hand, when the changing
1 P

lever 43 is lifted, the locking pin becorries insertable inro -he locking hole 42 under the biasing force exerted by the spring.
Moreover, in this construction, with the rear cover 2 0 held in the working position, the locking pin is located rearwardly and away from the locking hole 42. When the changing lever 43 is lifted with the locking pin kept in this location, the locking pin is pressed against the surface of the resiliently lowering rod 28 under the biasing force exerted by the spring and, when the rear cover 20 is lifted upward from the working position, the rod holder 32 is shifted forwardly relative to the resiliently lowering rod 28. Then, upon alignment with the locking hole 42, the locking pin is automatically inserted into the locking hole 42 under the biasing force exertedby the spring, thus restraining the relative movement between the resiliently lowering rod 28 and the rod holder 32. In consequence, the rear cover 20 remains upward in the posiuion to which it was moved from the working position.
As shown in Fig. 3, the gas spring 27 is composed of a tube 46, a piston 47 disposed inside the tube 46 in an axially shiftable manner (longitudinally shiftablemanner) , andapiston rod 48 which is moved unitarily with the piston 47 . The interior of the tube 46 is divided by the piston 47 into a rod-side chamber 4 6A and a bottom-side chamber 4 6B. The rod-side chamber 46A and the bottom-side chamber 46B of the interior of the tube 4 6 are corroxLunicated with each other through an orifice 4 9 form.ed
' Q

in the piston 47. The tube 46 is filled v/iun a corrpressed gas serving as a biasing element.
A rod-side pressure recei\^ing surface of the piston 47 is smaller than a bottom-side pressure receiving surface thereof in terms of area for receiving the compressed gas contained within the tube 46. By a degree corresponding to the difference in pressure-receiving surface area, the piston rod 48 exhibits a repulsive force constantly in its elongation direction.
Note that the gas spring 27 may employ any other structure so long as it is designed so that the piston rod 48 can be urged in the elongation direction by the compressed gas . For example, the gas spring 27 may include the tube 46 which contains oil.
In the gas spring 27, at the bottom-side end of the tube 4 6 and at the front end of the piston rod 48 are disposed ball joints 53 and 54 (joint members) , respectively. The ball joint 53 has an attachment portion 51 (lock) and a spherical joint portion 50A. The ball joint 54 has an attachment portion 52 (lock) and a spherical joint portion 50B.
As shown in Figs. 1 to 5, with the rear cover 20 held in the working position, the gas spring 27 is in a state of extending rearward (nearly horizontal or weakly inclined state) and is in juxtaposition with the rear cover 20 with respect to a vertical direction.
Moreover, in this embodiment, the gas spring 27 is so disposed that the tube 4 6 is located on the front side thereof
20

and "che rearwardly protruding piston rod 4 8 is free zo advance from and retract into the tube.
On that side of the machine frame-side bracket 30 which is located outwardly with respect to a horizontal direction, there is disposed-a link 65 having its one end side (anterior end side) attached to the anterior end side of the gas spring 27 and its other end side (rear end side) pivotally supported on the machine frame-side bracket 30.
Of the side walls 30a of the machine frame-side bracket 30, the one 30a located outwardly with respect to a horizontal direction is fitted with a horizontally outwardly protruding support cylinder 64 lying below the pivot shaft 33.
The support cylinder 64 has a horizontal axis. A fulcrum shaft 66, which is fixed to the other end side (rear end side) of the link 65 made of a plate, is inserted through the support cylinder 64 in an axially rotatable manner. The fulcrum shaft 66 passes through the machine frame-side bracket 30 and is retained in position. The rear end side of the link 65 is supported via the fulcrum shaft 66 on the machine frame-side bracket 30 and the support cylinder 64 for free turning movement about a horizontal axis.
Moreover, fixedly attached to one end side (anterior end side) of the link 65 is the attachment portion 51 of the tube 46's bottom-side ball joint 53. The anterior end side of the tube 4 6 is attached to the anterior end side of the link 65 for
21

i.re6 turning movement aioOL
The tube 4 5 of the gas spring 27 is designed to turn about the axis of the fulcrum shaft 66 in conjunction with the link 65. The axis of the fulcrum shaft 66 is defined as a tube 4 6-side pivotal point X of the gas spring 27 (a tube 46-side turning fulcrum point X of the gas spring 27) . As shown in Fig. 4, the tube 46-side pivotal point X of the gas spring 27 is located inwardly relative to the attachment portion 51 of the ball joint 53 at the tube bottom side of the gas spring 27 with respect to the direction of the length of the gas spring 27.
Moreover, in the construction as illustrated in Figs. 1 to 5, the tube 46-side pivotal point X of the gas spring 27 is located inwardly relative to a bottom-side end 46C of the tube 46 with respect to the direction of the length of the gas spring 27 (in other words, the tube 46-side pivotal point X of the gas spring 27 is located between the bottom-side end 4 6C and a piston rod-side end 46D of the tube 4 6, and is situated nearer the bottom-side end 4 6C in relation to the center of the tube 4 6 between the bottom-side end 4 6C and the piston rod-side end 46D) .
Further, the biasing force exerted by the biasing element of the gas spring 27 tends to push the piston rod 48 in a rearward direction. A biasing force-receiving portion (a portion subjected to the biasing force exerted by the biasing element) at the lengthwise bottom side -of the interior of the tube 4 6 is located outwardly relative to the pivotal point X of the gas
22

spring 21 which lies on the same side as rhe biasing force-receiving portion does, with respect to the direction of the length of the gas spring 27.
When viewed from one end of the gas spring 27, the inward reach with respect to the direction of the length of the gas spring 27 corresponds to a direction from the attachjnent portion 51, 52 at one end side of the gas spring 27 to the attachment portion 51, 52 at the other end side thereof. On the other hand, when viewed from the other end of the gas spring 27, the inward reach with respect to the direction of the length of the gas spring 27 corresponds to a direction from the attachment portion 51, 52 at the other end side of the gas spring 27 to the attachment portion 51, 52 at one end side thereof. (For example, when viewed from the bottom of the tube 4 6 of the gas spring 27, the inward reach corresponds to a direction from the attachment portion
51 at the bottom side of the tube 4 6 to the attachment portion
52 at the front end of the piston rod 48 of the gas spring 27. On the other hand, when viewed from the front end of the piston rod 48 of the gas spring 27, the inward reach corresponds to a direction from the attachment portion 52 at the front end of the piston rod 48 to the attachment portion 51 at the bottom side of the tube 46 of the gas spring 27.
Note that the outward reach with respect to the direction of the length of the gas spring 27 is reverse to the inward reach with respect to the direction of the length of the gas spring
23

27 described just above.
The tube 4 6 of the gas spring 2 7 is located above the pivored portion 24 of the rear cover 20, and the tube 46-side pivotal point X of the gas spring 27 is located above and forward of the turning fulcrum 25 of the rear cover 20.
Note that the fulcrum shaft 66 may be disposed directly on the tube 46 without interposition of the link 65. In this case, the tube 46 is pivotally mounted directly on the machine frame-side bracket 30 (or a member fixed to the machine frame-side bracket 30).
The front end side of the piston rod 48 of the gas spring 27 (the rear end side of the gas spring 27) is pivotally coupled to a lever 57 disposed on the rear cover-side bracket 31 (biasing force changing member) for free turning movement about a horizontal axis. The front end side of the piston rod 48 of the gas spring 27 is thus pivotally supported on the rear cover-side bracket 31 via the lever 57.
The base end side (one end side) of the lever 57 is attached relatively to a lever support portion 58 for free turning movement about a horizontal axis. The lever support portion 58 is formed of a plate secured to one of the side plates 31a of the rear cover-side bracket 31 that is located horizontally outwardly. Fixedly attached to the front end side (the other end side) of the lever 57 is the attachment portion 52 of the ball joint 54 at the front end of the piston rod 48 of the gas spring 27.
24

.ever 57, a cylindrical member 59 is secured and an insertion hole 60 communicating with the interior of the cylindrical member 59 is formed. Moreover, a horizontally protruding pin 61 is secured to the lever support portion 58. The cylindrical member 59 is fitted at the outside of the pin 61 in an axially rotatable manner. The pin 61 is so formed as to protrude through the insertion hole 60 and has its front end side fitted with a retention member 62. In this way, the lever 57 is freely turnably supported on the lever support portion 58.
Note that, in the construction thus far described, the link 65 may be disposed on the rear cover-side bracket 31, and also the lever support portion 58 and the lever 57 may be disposed on the machine frame-side bracket 30; that is, the gas spring 27 may be turned upside down in an anteroposterior direction.
It is also possible to dispose the link 65 so that it is pivotally supported on either one of the machine frame-side bracket 30 and the rear cover-side bracket 31 while coupling the attachment portion 52 of the ball joint 54 at the front end of the piston rod 48 to the link 65, with the attachment portion 51 of the ball joint 53 at the bottom of the tube 46 attached to the other one of the machine frame-side bracket 30 and the rear cover-side bracket 31. That is, it is essential only that the pivotal point at one end side or the other end side of the gas spring 27 be displaced inwardly from the attachment portion

51, 52 of the gas spring 27 that lies on the same side as th pivotal point does, with respect to the direction of the lengrh of the gas spring 27.
In another alternative, the link 65 may be disposed on the machine frame-side bracket 30 and on the rear cover-side bracket 31. In this case, the gas spring 27 is pivot ally supported via the link 65 on the machine frame-side bracket 30 and the rear cover-side bracket 31.
With the rear cover 20 held in the working position, as shown in Fig. 3, where a pivotal point Y at the front end side of the piston rod 48 (the center of turning movement of the ball joint 54; the piston rod 48-side turning fulcrum point of the gas spring 27) is located below a dead line L (dead point) passing through the tube 46-side pivotal point X of the gas spring 27 and a turning fulcrum point Z of the lever 57 (the center of turning movement of the lever 57), then the gas spring 27 is actuated in a direction to rock the lever 57 downwardly, while the lever 57 is restrained from the downward turning movement by a stopper 53 disposed on the rear cover-side bracket 31 (or disposed on the lever support portion 58 ) . Under this condition (biased condition) , the biasing force of the gas spring 27 sets upon the rear cover 20 through the lever 57, the stopper 63, and the rear cover-side bracket 31, so as to tend to rock the rear cover 2 0 in a downward direction (in a direction of contact with the around).

Moreover, as shown in Fig. 3, as the lever 57 is so operated as to turn upwardly from a force-acting area W in which the biasing force of the gas spring 27 tends to rock the rear cover 20 downwardly, the pivotal point Y at the other end side of the gas spring 27 is shifted upwardly above the dead line L correspondingly. At this time, the biasing force of the gas spring 27 acts in a direction to turn the lever 57 backwardly, thus bringing the gas spring 27 into a fully stretched state. In consequence, there is established the .freed condition where the biasing force of the gas spring 27 no longer sets upon the rear cover 20.
Accordingly, the turning operation (switching operation) of the lever 57 allows easy selection between the biased condition where the biasing force of the gas spring 27 sets upon the rear cover 20 and the freed condition where the biasing force of the gas spring 27 no longer sets upon the rear cover 20.
Moreover, the lever 57 has formed at its front end side a plurality of attachment holes 67 (although there are 3 in number in this embodiment, two or four or more holes may be provided) for attachment of the attachment portion 52 of the ball joint 54 at the front end of the piston rod 48. This makes it possible to render the pivoted position at the end of the gas spring 27 changeable, and thereby vary the biasing force exerted by the gas spring 27 upon the rear cover 20.
Note that, as shown in Fig. 7, under the biased condition, the biasing force of the gas spring 27 acts in a direction to
27

rock the rear cover 20 downwardly over the whole range that the rear cover 20 is allowed to rock up and down. On the other hand, as shown in Fig. 8, under the freed condition, the biasing force of the gas spring 27 no longer sets upon the rear cover 20 over the whole range that the rear cover 20 is allowed to rock up and down.
In the foregoing embodiment, by setting the gas spring 27 in the biased condition while preventing the resiliently lowering device 26 from exerting a biasing force on the rear cover 20, it is possible for the rear cover 20 to be urged in the direction of contact with the ground only by the biasing force of the gas spring 27. Moreover, by setting the gas spring 27 in the freed condition while allowing the resiliently lowering device 26 to exert a biasing force on the rear cover 20, it is possible for the rear cover 20 to be urged in the direction of contact with the ground only by the biasing force of the resiliently lowering device 26. Further, it is also possible to operate the gas spring 27 and the resiliently lowering device 26 in such a manner that their biasing forces are exerted on the rear cover 20 together or are inhibited from exerting on the rear cover 20 together.
Moreover, in the case where the rear cover 20 is actuated only by the resiliently lowering device 2 6, the following problems may arise: the degree of the biasing force of the resiliently lowering device 2 6 is varied greatly according to the position
28

of the rear cover 2 0 in a vertical direction, or the biasing-force acting range may become narrower, and thus there is the need for re-positioning of the spring bearing member 37 depending upon the position of the rear cover 20 in the vertical direction. In contrast, in the case where the rear cover 20 is actuated only by the biasing force of the gas spring 27, the biasing force can be exerted substantially uniformly on the rear cover 20. As another advantage, the range of actuation of the rear cover 20 can be widened without the necessity of adjustment of the biasing force.
Moreover, in the gas spring 27, at the time of contraction, the pressure within the tube 4 6 is raised by a degree corresponding to the volume of the inserted piston rod. In this regard, in this embodiment, with the rear cover 20 held in the working position, the gas spring 27 is in a nearly horizontal, weakly inclined state or is set horizontal. Therefore, even if up-and-down rocking motions are imparted to the rear cover 20 in the working position, the gas spring 27 is changed little in length, in consequence whereof there results little variation in the biasing force of the gas spring 27.
Moreover, under the biased condition, the gas spring 27 is contracted gradually with the upward movement of the rear cover 20, and is in a state of extending obliquely in a rearward direction when the rear cover 2 0 assumes the uppermost position. As shown in Fig. 15, in a case where the tube 4 6-side joint of
9Q


ring 2 7 is pivotally coupled ~o "the rriachme frame-side bracket 30 and the piston rod 48's front end-side joint of the gas spring 27 is pivotally coupled to the rear cover-side bracket 31, depending on the location of the uppermost position of the rear cover 20, the gas spring 27 reaches the limit of its contraction (the length of the gas spring is reduced to a minimum) and the piston 47 may therefore be brought into abutment with the end of the interior of the tube 46. In this regard, in this embodiment, the tube 46-side pivotal point X of the gas spring 27 is displaced inwardly from the attachment portion 51 at the tube bottom side of the gas spring 27 with respect to the direction of the length of the gas spring 27. With such an arrangement, the attachment portion 51 at the tube bottom side of the gas spring 27 is located outwardly away from the tube 46-side pivotal point X of the gas spring 27 with respect to the direction of the length of the gas spring 27 (or the biasing force-receiving portion at the bottom side of the tube 46 is located outwardly relative to the pivotal point X of the gas spring 27 that lies on the same side as the biasing force-receiving portion does, with respect to the direction of the length of the gas spring 27) . This makes it possible to avoid that the piston 47 abuts against the end of the interior of the tube 46 (the length of the gas spring 27 is reduced to a minimum) in the uppermost position of the rear cover 20, or makes it possible to set the uppermost position of the rear cover 20 at a higher level.

Moreover, in the construction as snov/n in Fig. 15, vnen, with the rear cover 20 held in the uppermost position, the tube 46-side pivotal point of the gas spring 27 (attachment portion) is shifted longitudinally (axially) downwardly from its location shown in Fig. 15, then the interval between the piston 47 and the bottom-side end of the interior of the tube 46 in the uppermost position is increased, thus preventing the length of the gas spring from being reduced to a m.inim.um in the upperm.ost position of the rear cover. In this case, however, with the rear cover 20 held in a lowermost position, the tube 4 6 may abut against the rear end of the rear cover 20 or the main cover 19. This gives rise to a problem such as the impossibility of lowering the rear cover 20 to a large extent or the risk of deformation of the pivoted portion 24 of the rear cover 20 (or the rear end side of the main cover 19) and so forth. However, the foregoing embodiment is free from such a problem; that is, it succeeds in overcoming the problem of the impossibility of lowering the rear cover 20 to a large extent or in preventing occurrence of deformation of the pivoted portion 24 of the rear cover 20 that is caused by the abutment of the tube 46 of the gas spring 27 against the vicinity of the pivoted portion 24 of the rear cover 20.
Note that, in the construction as shown in Fig. 15, in the case of setting the rear cover 20 in the uppermost position, it seems that, just as is the case with the present embodiment.

there will arise no probiem so long as the biasing force exerueo by the gas spring 27 upon the rear cover 20 is releasable . However, if the biasing force exerted by the gas spring 27 upon the rear cover 20isleftunreleased, orifthe depth of plowing is increased while the rear cover 20 is being caught in ridges during cultivating operation, the rear cover 20 may inconveniently assume the uppermost position.
Furthermore, some tractors are provided with a plowing-depth control device for controlling the depth of plowing by lifting and lowering the cultivating apparatus 1 on the basis of the amount of up-and-down rocking motions of the rear cover 20 . According to the cultivating apparatus 1 of this embodiment, when the rear cover 20 is pushed upward by the soil cultivated by the cultivating section 3 or stones in agricultural fields, by operating the gas spring 27 in such a manner as to provide a resistance against the compression of the coil spring 29 of the resiliently lowering device 26, it is possible to retard the compression of the coil spring 29. On the other hand, when the rear cover 20 makes return movement (is lowered) , by operating the gas spring 27 in such a manner as to provide a resistance against the return (restoration) of the coil spring 29 of the resiliently lowering device 26 to its original state, it is possible to retard the restoration of the coil spring 29.
In this way, the gas spring 27, while acts to suppress speeding up and an increase in magnitude of oscillation of the

upv-zard rriovement of the rear cover 2 0 when the rear cover 2 0 is moved upward under the influence of soil-inducedpressure, stones, and so forth, acts to suppress speeding up and an increase in magnitude of oscillation of the downward movement of the rear cover 20 when the rear cover 20 is moved downv7ard. This makes it possible to decay the up-and-down movement of the rear cover 20, as well as to reduce the number of times that the rear cover 20 is driven to rock consecutively.
That is, in contrast to the case of actuating the rear cover 20 only by the resiliently lowering device 26, in the case of using the resiliently lowering device 26 and the gas spring 27 in combination, it is possible to slow down the up-and-down rockingmotions of the rear cover 20 in the course of cultivation. In addition, in the case of exercising the plowing-depth control on the basis of the detection of the up-and-down movement of the rear cover 20, since excessive responsiveness can be avoided, satisfactory plowing-depth control can be achieved.
Note that, instead of the gas spring 27 of the embodiment having the foregoing structure, it is possible to employ a pressing device in which a rod-shaped extendable member that is free to extend and contract lengthwise is urged in its elongation direction by a spring (biasing element).
In Figs. 9 to 11, there is shown another embodiment of the construction in which the rear cover 20 is actuated by the gas spring 27. In this emlsodim.ent, the front end side of the
33

piston roQ 48 1; _ bracket 30, and the tube 4 5 of the gas spring 27 is supported on a tube holder 71 for relative axial movement. The tube holder 71 is supported on the rear cover-side bracket 31 for free turning movement about a horizontal axis . In addition, there is provided a locking mechanism 72 that, while restrains the movement of the tube 46 relative to the tube holder 71 to achieve the biased condition where the biasing force of the gas spring 27 sets upon the rear cover 20, permits the movement of the tube 4 6 relative to the tube holder 71 to achieve the freed condition where the biasing force of the gas spring 27 no longer sets upon the rear cover 20 in a manner to allow selection between the biased condition and the freed condition.
Fixed to the machine frame-side bracket 30 is a stay 73 to which is attached the attachment portion 52 of the ball joint 54 at the front end of the piston rod 48.
The tube holder 71 is composed of an outer constituent body 74, a fulcrum shaft 75 disposed on the outer constituent body 74, and an inner constituent body 76 disposed within the outer constituent body 74.
The outer constituent body 7 4 is composed of an inward side wall 74a, an outward side wall 74b spaced horizontally outwardly from the inward side wall 74a, an upper wall 74c acting as the connection between the top of the inward side wall 74a and the top of the outward side wall 7 4b, and a lower wall 7 4d
j^

extending horizontally inwardly f ron the lower end of the outward side well 74b. The outer constituent body 74 has a hollow structure with its front and rear surfaces opened.
Note that the outward side wall 74b, the upper wall 74c, and the lower wall 7 4d are formed in a single-piece structure.
Between an inner edge 77 of the lower wall 74d and the inward side wall 74a is formed a gap 78 along an anteroposterior direction. The gap 7 8 is so shaped that its width becomes larger gradually from substantially the anteroposterior center to the rear of the outer constituent body, and the rear end of the lower wall 74d coincides with the rear end of the outward side wall 74b.
Moreover, in the rear part of the lower wall 74d is formed a first guide slot 7 9 which extends from the inner edge 77 to the outward side wall 74b in a forwardly inclined manner in a horizontally outward direction. The outward side wall 7 4b is formed with a second guide slot 80 extending vertically from the lower end partway to the upper end thereof in a forwardly inclined manner in an upward direction. The first guide slot 7 9 and the second guide slot 80 merge with each other.
The fulcrum shaft 75 is formed in an anteroposterior intermediate part of the inward side wall 74a of the outer constituent body 74 so as to protrude inwardly in a horizontal direction.
In the meanwhile, a support base 81 having a U-shaped cross

sectional profile is secured to the rear cover-side bracket 31, Fixed to the rear part of the support base 81 is a support cylinder 82 having a horizontal axis. The fulcrum shaft 75 is inserted through the support cylinder 82 and is retained in position. In this way, the tube holder 71 is supported for free turning movement about rhe axis of the fulcrum shaft 75.
The tube 4 6 is made free to turn about the fulcrum shaft 75. The axis of the fulcrum shaft 7 5 is defined as the tube 46-side pivotal point X of the gas spring 27.
The inner constituent body 7 6 is formed by cutting away part of a cylindrical body having opened axial opposite ends. The inner constituent body 76 is inserted in the front part of the outer constituent body 74 interiorly thereof and secured to the outer constituent body 74, with its axial one end pointing frontward and its axial other end pointing rearward.
The inner constituent body 7 6 is mounted in a notch 83-downward fashion.
The tube 46 of the gas spring 27 is inserted through the inner constituent body 76 in an axially shiftable manner. In this way, the tube 46 of the gas spring 27 is supported on the tube holder 71 in an axially shiftable manner.
A grip 84 is detachably attached to the attachment portion 51 of the ball joint 53 at the end of the tube 46.
With the grip 84 oriented downward (pointing downward), the tube 4 6 is free to slide axially within the inner constituent
36

body 76 and is extendable rearwaraly rrom tne tuoe nc^der 71, yet is inhibited from coming out frontwardly of the tube holder 71 by the abutment of the attachment portion 51 against the horizontally inner end of the first guide slot 79.
In order for the tube 4 6 to be inserted into the inner constituent body 7 6, the grip 84 is removed and the attachment portion 51 is tilted, whereby the tube 46 is insertable into the inner constituent body 7 6 through the notch 83 of the inner constituent body 76 and the gap 78 of the outer constituent body 74.
In the embodiment thus constructed, with a grasp of the grip 84, the attachment portion 51 of the tube 4 6-side ball joint 53 is shifted from the first guide slot 79 toward the end of the second guide slot 80, whereupon the gas spring 27 is inhibited from further axial movement relative to the tube holder 71, and the insertion of the piston rod 48 of the gas spring 27 is effected to achieve the biased condition. In this way, the rear cover 20 can be urged in a downward direction.
In contrast, by moving the attachment portion 51 away from the second guide slot 80 and the first guide slot 79 so as for the grip 84 to be oriented downward, it is possible to achieve the freed condition where the biasing force of the gas spring 27 no longer sets upon the rear cover 20.
The locking mechanism 72 is composed of the first and second guide slots 79 and 80, the attachment portion 51 of the ball
37

joint 53 at ~he end of the tube 4 6, rhe grip 84, and sc forcn.
Otherv/ise, the present embodiment is sim.ilar in structure to the preceding embodiment shown in Figs. 1 to 8.
In Figs. 12 to 14, there is shown still another emibodiment of the construction in which the rear cover 20 is actuated by the gas spring 27. In this emibodiment, a support cylinder 86, which is fitted at the outside of the tube 46 for free relative axial movement, is supported on the miachine framie-side bracket 30 for free turning movement about a horizontal axis. Moreover, the machine frame-side bracket 30 is provided with a first guide m.ember 8 7 for guiding the bottom-side end of the tube 4 6 in such a manner that it follows the up-and-down movement of the rear cover 20 while controlling the position of the bottom-side end of the tube 46. Further, the rear cover 20-side bracket 31 is provided with a positioning member 88 that, while effects positioning of the front end of the piston rod 48 so as to achieve the biased condition where the biasing force of the gas spring 27 sets upon the rear cover 20, achieves the freed condition where the biasing force of the gas spring 27 no longer sets upon the rear cover 20by releasing the said positioning. In addition, the rear cover 20-side bracket 31 is provided with a second guide member 8 9 for supporting the front end side of the piston rod 48 under the freed condition and guiding the front end side of the piston rod 48 in such a manner that it follows the up-and-down movement of the rear cover 20.
38

inwardly protruding fulcrum shaft 90 having a horizontal axis. The fulcrum shaft 90 passes through the machine frame-side bracket 30 and is axially positioned by a positioning member 91 located on both horizontal sides of the machine frame-side bracket 30. In this way, the support cylinder 8 6 is supported for free turning movement about a horizontal axis.
The axis of the fulcrum shaft 90 is defined as the tube 46-side pivotal point X of the gas spring 27.
Moreover, fixed to the attachment portion 51 of the ball joint 53 at the end of the tube 46 is a to-be-guided member 93 having a collar 92.
The first guide member 87 is formed with a circularly arcuate first guide slot 94 . In this construction, as the collar 92 of the to-be-guided member 93 is inserted into the first guide slot 94, the tube bottom-side end of the gas spring 27 can be guided by the first guide member 87.
The second guide member 89 is formed with a second guide slot 95 for guiding the ball joint 54 at the front end of the piston rod 48, which is so formed as to elongatedly extend substantially in line with a direction axially of the gas spring 27.
On one end side of the positioning member 88 is disposed a turning shaft 96 having a horizontal axis. With the insertion of the turning shaft' 96 into a cylindrical portion 97 disposed
39

above the anterior end side of the second guide member 5 5, zhe positioning member 8 8 can be mounted for free turning miovement about a horizontal axis.
Moreover, on the other end side of the positioning member 8 8 is disposed a hold-down cylinder 98.
The positioning member 88 is, when the front end of the piston rod 48 of the gas spring 27 is located on the anterior end side of the second guide slot 95, contacted from behind by the ball joint 54 at the front end of the piston rod 48, and is secured unturnably by a hold-down pin 99 which is inserted through the hold-down cylinder 98 at the other end of the positioning member 88 and passes through the rear cover 20-side bracket 31, so that the front end of the piston rod 4 8 is positioned while being restrained f rommovement relative to the second guide member 89. In this state, there is established the biased condition where the rear cover 20 is urged in a dcvjnv.'ard direction by the gas spring 27.
Moreover, with the hold-down pin 99 removed out, the positioning member 88 is driven to turn upwardly until it reaches a position such as not to cross over the second guide slot 95, whereupon the ball joint 54 at the front end of the piston rod 48 comes to be free to move along the second guide slot 95. In consequence, there is established the freed condition where the gas spring 27 ceases from acting to exert a biasing force upon the rear cover 20.
4 0

Note that, on the top surface of the rear part of the second guide nnember 89 is disposed a holding cylinder 100. With the insertion of the hold-down pin 99 through the holding cylinder 100 as well as the hold-down cylinder 98 at the other end of the positioning member 88, it is possible to retain the positioning member 88 under the freed condition.
Otherwise, the present embodiment is similar in structure to the preceding embodiment shown in Figs. 1 to 8.
In Figs. 16 and 17, there is- shown a modified example of the construction in which the rear cover 20 is actuated by the gas spring 27 in accordance with the embodiment shown in Figs. 1 to 8.
In the construction shown in Figs. 1 to 8 in which the rear cover 20 is actuated by the gas spring 27, under normal circumstances, when the rear cover 20 is driven to rock up and down, the link 65 and the tube 4 6 turn unitarily about the fulcrum shaft 66 in accompaniment with the up-and-down rocking motions of the rear cover 20. However, if the rear cover 20 is lowered so abruptly that the extending action of the gas spring 27 cannot keep up with the lowering movement of the rear cover 20, the link 65 will be pulled by the gas spring 27 and thus caused to rock downwardly about the fulcrum shaft 66, with the result that the gas spring 27 may possibly drop down for a moment. Such a drop of the gas spring 27 results in the possibility that the gas spring 27 abuts against the rear end side of the rear cover
41

2 0 or the main cover 19 and the like.
Accordingly, in the construction shown in Figs. 16 and 17, in order for the link 65 and the tube 4 6 to turn unitarily about the fulcrum shaft 66 at all times, there is provided an engagement member 102 for establishing a linkup between the link 65 and the tube 46. In this respect, the construction shown in Figs. 16 and 17 differs from the construction shown in Figs. 1 to 8 in v;hich the rear cover 20 is actuated by the gas spring 27. Otherwise, the present construction is similar in structure to the construction shown in Figs. 1 to 8.
The engagement member 102 is formed by bending a slim, strip plate-like spring member, and is composed of a linear fixed piece 103 and a pair of engagement pieces 104. The engagement pieces 104 extend from the lengthwise opposite ends, respectively, of the f ixedpiece 103 so as to confront each other in the direction of the length of the fixed piece 103.
The fixed piece 103 of the engagement member 102 is so disposedthat its longitudinal edge is alignedwith the transverse edge of the link 65, and is fixed, on the rear side of the link 65, to one side surface of the link 65 opposite from the other side surface thereof to which is secured the fulcrum shaft 66. The engagement pieces 104 confront each other with respect to a top to bottom direction (a direction diametrically of the tube 46) . The upper and lower engagement pieces 104 have sandwiched therebetween the tube 46 of the aas sprina 27.
4 2

Moreover, the upper and lower engagement pieces 104 are oppositely curved at their lengthwise intermediate portions to conform to the shape of the outer periphery of the tube 46 of the gas spring 27. The interval between the front ends, respectively, of the engagement pieces 104 is set to be shorter than the diametrical width of the tube 46 of the gas spring 27. As the engagement pieces 104 become elastically deformed so that a spacing therebetween is widened, the tube 4 6 can be inserted into the region between the engagement pieces 104.
With the provision of the engagement member 102, it is possible to achieve the link-up of the link 65 and the tube 46, whereby they can turn unitarily about the fulcrum shaft 66 at all times. Accordingiy, even if the rear cover 20 is about to be lowered abruptly, the link 65 and the gas spring 27 are allowed to turn unitarily about the fulcrum shaft 66 while following the rocking motions of the rear cover 20 without fail.
Note that the engagement member 102 may be formed of a slim, round bar-shaped spring member such as a piano wire . Note also that the engagement member 102 does not necessarily have to be formed of a spring member.
Figs. 18 and 19 show another embodiment of the pressing device 27'. The pressing device 27 of this embodiment includes a rod 106 pivotally supported on the machine frame-side bracket 30 and the rear cover 20-side bracket 31 and a coil spring 107 serving as a biasing element that is set surroundingly around
43

the rod 106 . The pressing device 27 is so formed as to elcr.garedly extend in a direction axially of the rod 106.
On lengthwise one side (axially anterior end side) of the rod 106 is disposed a horizontally inwardly protruding attachment portion 108 made of a bar material.
The attachment portion 108 has a male thread 108a formed on the horizontally inward side thereof. The male thread 108a is inserted through an insertion hole 65a form.ed on one end (anterior end) side of the link 65.
Moreover, a pair of nuts 109 located on both horizontal sides of the link 65 are threadedly engaged with the male thread 108a of the attachment portion 108. By fastening the nuts 109, one end side of the link 65 is f ixedrelatively to one side (anterior end) of the rod 106.
Further, a horizontally protruding fulcrum shaft 66 is fixedly attached to the other end (rear end) side of the link 65.
The fulcrum shaft 66 is inserted through a support cylinder 64 disposed on one of the side walls 30a of the machine frame-side bracket 30 that is locatedhorizontally outwardly, andalsopasses through the right-hand and left-hand side walls 30a of the machine frame-side bracket 30. The fulcrum shaft 66 is retained by a retention pin or the like so that it is inhibited from coming out of the support cylinder 64 and the machine frame-side bracket 30.
Z!4

The fulcrum shaft 66 is supported on the support cylinder 64 and the machine frame-side bracket 30 for free rotation about a horizontal axis.
In this way, the front part of the rod 106 is supported via the link 65 on the machine frame-side bracket 30 for free turning movement about the axis of the fulcrum shaft 66.
The axis of the fulcrum shaft 66 is defined as a pivotal point X on the front side of the pressing device 27. That is, the front part of the pressing device 27 is pivotally supported at a position located inwardly relative to the attachment portion 108 with respect to the direction of the length of the rod 106.
Moreover, the rod 106 has its lengthwise other side (axial rear side) supported by a rod holder 110 pivotally supported on the rear cover-side bracket 31.
The rod holder 110 is composed of a cylindrical portion 110a through which is inserted the rod 106 in an axially shiftable manner and a pivot portion 110b formed so as to protrude horizontally inwardly from the cylindrical portion 110a.
The pivot portion 110b of the rod holder 110 is inserted through a holding cylinder 111 secured to one of the side plates Slaoftherear cover-side bracket 31 that is located horizontally outwardly, and also passes through the right-hand and left-hand side plates 31a of the rear cover-side bracket 31. In this state,' the pivot portion 110b is supported for free rotation about a horizontal axis on the holding cylinder 111 and the rear

cover-side bracket 31.
Accordingly, the rear side of the rod 10 6 is pivotally supported on the rear cover-side bracket 31 via the rod holder 110.
At the rear end of the rod 10 6 is disposed an abutment
112 which restrains the downward rocking motion of the rear cover
20 by making contact with the rear surface of the cylindrical
portion 110a of the rod holder 110.
In the pressing device 27 thus constructed, as the rear cover 20 is driven to rock up and down, the rod 106 rocks about the fulcrum shaft 66 and is also shifted axially relative to the cylindrical portion 110a of the rod holder 110, thereby permitting the up-and-down rocking motions of the rear cover 20.
On the anterior end side of the rod 106 is disposed a spring bearing member 113 so as to be located forward of the fulcrum shaft 66.
As shown in Figs. 18 and 19, the spring bearing member
113 is positioned forward of the fulcrum shaft 66 (positioned
outwardly relative to the fulcrum shaft 66 with respect to the
direction of the length of the rod 106) and fixed relatively
to the rod 106 in an axially unshiftable manner.
Between the spring bearing member 113 and the cylindrical portion 110a (the front- face of the cylindrical portion 110a) of the rod holder 110 is interposed the coil spring 107 held
46

in compression . The rear cover 2 0 is urged in a downward direction under the biasing force exerted by the coil spring 107.
Note that the spring bearing member 113 may be so designed as to be positionable in a plurality of axial locations of that part of the rod 106 which is located forward of the fulcrum shaft 66. In this case, it is possible tomake adjustment to the biasing force of the coil spring 107.
Otherwise, the present embodiment is simiilar in structure to the preceding embodiments . Also in this embodiment, one side of the pressing device 27 is pivotally supported on the same-side bracket 30 in such a manner that a biasing force-receiving portion at one side of the pressing device 27 (that part of the spring bearing member 113 which is contacted by the coil spring 107) is located outwardly relative to the pivotal point X of the pressing device 27 that lies on the same side as the biasing force-receiving portion does, v.'ith respect to the direction of the length of the pressing device 27.
Moreover, the attachment portion 108 disposed lengthwise one side of the pressing device 27 is fitted with one end side of the link 65, and the other end side of the link 65 is pivotally supported on the bracket 30, which lies on the same side as the attachment portion 108 to which is attached one end side of the link 65 does, at a position located inwardly relative to the attachment portion 108 to which is attached one end side of the link 65 with respect to the direction of the length of the pressing
47

As will be understood from the foregoing, in contrast to the case where the attachment portion 108 is pivotally supported directly on the machine frame-side bracket 30 (without the interposition of the link 65) at the same position as that of the fulcrum shaft 66, in the construction as shown in Figs. 18 and 19, the uppermost position of the rear cover 20 can be set at a higher level.
Moreover, in a case where the pivotal point X is set in alignment with the attachment portion 108 (where a stay is formed so as to protrude forwardly from the machine frame-side bracket 30 along the rod 106 and the attachment portion 108 is pivotally supported directly on the stay) , when the rear cover 20 assumes the lowermost position, there arises the problem of deformation of the pivoted portion 24 of the rear cover 20 because of the abutment of the rod 10 6 against the vicinity of the pivoted port ion 24. However, in the construction as shown in Figs. 18 and 19, even if the rear cover 20 assumes the lowermost position, it never occurs that the rod 106 abuts against the vicinity of the pivoted portion 24 of the rear cover 20.
That is, in contrast to the case of setting the pivotal point X in alignment with the attachment portion 108, in this construction, the advantage is gained that the rear cover 20 can be lowered to a larger extent or the pivoted portion 24 of the rear cover 20 can be protected from deformation caused by
48

the abutment of the rod 10 6 agains" the vicinity thereof when the rear cover 20 assumes the lowermost position.
The direction of the length of the pressing device 27 is identical with the direction of the length of the rod 106. The inward reach with respect to the direction of the length of the pressing device 27 corresponds to a direction from the end of the rod 106 to the axial center of the rod 106, whereas the outward reach with respect to the direction the length of the pressing device 27 corresponds to a direction from the axial center of the rod 106 to the end of the rod 106.
Also in this embodiment, by attaching the rod holder 110 to the rear cover-side bracket 31 via the aforestated lever 57 or the like, it is possible to render the biasing force exerted by the coil spring 107 upon the rear cover 20 releasable (achieve the freed condition where the biasing force of the coil spring 107 no longer sets upon the rear cover 20).
49

WHAT IS CLAIMED IS:
1. A cultivating apparatus comprising:
a machine frame (2);
a cultivating section (3) disposed below a main cover (19) attached to the machine frame (2);
a rear cover (20) for covering the rear part of the cultivating section (3), the anterior end side of which is supported on the rear end side of the main cover (19) for free turning movement about a horizontal axis to render the rear cover (20) freely rock able up and down; and
a long pressing device (27) having a biasing element for urging the rear cover (20) in a downward direction, which is pivotally supported on a bracket (30) disposed in a machine frame (2) side region and a bracket (31) disposed in a rear-cover side region to enable the rear cover (20) to rock upwardly against a biasing force exerted by the -biasing element,
wherein one side of the pressing device (27) is pivotally supported on the same-side bracket (30) in such a manner that a biasing force-receiving portion at one side of the pressing device (27) is located outwardly relative to a same-side pivotal point (X) of the pressing device (27) with respect to a direction longitudinally of the pressing device (27).
2. A cultivating apparatus comprising:
a machine frame (2);

a cultivating section (3) disposed below a main cover (15) attached to the machine frame (2);
a rear cover (20) for covering the rear part of the cultivating section (3), the anterior end side of which is supported on the rear end side of the main cover (19) for free turning movement about a horizontal axis to render the rear cover (20) freely rock able up and down; and
a long pressing device (27) having a biasing element for urging the rear cover (20) in a downward direction, which is pivotally supported on a bracket (30) disposed in a machine frame (2) side region and a bracket (31) disposed in a rear-cover side region to enable the rear cover (20) to rock upwardly against a biasing force exerted by the biasing element,
wherein at least an attachment portion (51, 108) at lengthwise one side of the pressing device (27) is 'fitted with one end side of a link (65) , and the other end side of the link (65) is pivotally supported on the bracket (30), which lies on the same side as the attachment portion (51, 108) to which is attached one end side of the link (65) does, in a position located inwardly relative to the attachment portion (51) to which is attached one end side of the link (65) with respect to a direction longitudinally of the pressing device (27).
3. The cultivating apparatus as set forth in claim 2,
wherein lengthwise one side of the pressing device (27)

is supported via the link (63) on the machine frame :2 -side bracket (30).
4. The cultivating apparatus as set forth in claim 2,
wherein lengthwise one side of the pressing device (27)
is supported via the link (65) on the rear cover (20)-side bracket (31) .
5. The cultivating apparatus as set forth in claim 1, 2, 3,
or 4, further comprising:
a biasing force changing member (57) for allowing selection between a biased condition where the biasing force produced by the biasing element of the pressing device (27) sets upon the rear cover (20) and a freed condition where the biasing force produced by the biasing element no longer sets upon the rear cover (20)
6. The cultivating apparatus as set forth in claim 1, 2, 3,
or 4,
wherein the pressing device (27) is built as a gas spring.
7. The cultivating apparatus as set forth in claim 1, 2, 3,
or 4,