Patent Description:
For example, the tractor disclosed in <CIT> (Patent Document <NUM>) is provided with a three-point link mechanism, and the three-point link mechanism is operated by a hydraulic unit (the "hydraulic lifting/lowering device" in the document) so as to swing. The work apparatus is configured to be able to move upward and downward according to a tow load when the work apparatus is attached to the three-point link mechanism and is towed by the vehicle body to perform ground work. A load receiving section (the "load detection member" in the document) that receives the tow load from the work apparatus is provided, and the load receiving section swings in response to the tow load from the work apparatus, and transmits an amount of operation for swinging the three-point link mechanism, to the hydraulic unit via the link mechanism. Also, an interlocking swing arm (the "swing member" in the document) that can swing in conjunction with the load receiving section is provided. When the load receiving section swings by a predetermined amount or more, the interlocking swing arm swings, the amount of swing of the load receiving section is amplified by the interlocking swing arm, and the operation sensitivity of the three-point link mechanism is improved.

In the tractor disclosed in <CIT>, the interlocking swing arm does not swing unless the load receiving section swings by the predetermined amount or more. That is to say, the operation sensitivity of the three-point link mechanism is not improved unless the tow load reaches an amount that is no less than the predetermined amount. Therefore, there is room for improvement in improving the operation sensitivity.

An object of the present invention is to provide a tractor capable of performing control to lift and lower a work apparatus with high sensitivity in response to a tow load.

A tractor according to the present invention includes: a three-point link mechanism that is coupled to a rear portion of a vehicle body so as to be able to swing upward and downward, and to which a work apparatus is to be attached so as to be able to move upward and downward; a hydraulic unit configured to perform a swing operation to swing the three-point link mechanism; a load receiving section configured to swing in response to a tow load being applied from the work apparatus when the work apparatus performs ground work while being towed by the vehicle body; and a link mechanism configured to transmit an amount of operation for the swing operation to the hydraulic unit according to an amount of swing of the load receiving section, wherein the link mechanism includes, at a most upstream position, an interlocking swing arm configured to swing in conjunction with the swing of the load receiving section, about a swing axis that is different from a swing axis of the load receiving section, the load receiving section is provided with a first part configured to press the interlocking swing arm, the interlocking swing arm is provided with a second part configured to come into contact with the first part so as to be pressed by the first part, and a contact position of the first part and the second part is changeable.

According to the present invention, the load receiving section and the interlocking swing arm respectively swing about different swing axes, and the contact position of the first part and the second part is changeable. Therefore, the link mechanism can amplify the amount of swing of the load receiving section by changing the contact position. Also, the interlocking swing arm is provided at the most upstream position in the link mechanism, and therefore the interlocking swing arm starts swinging when the load receiving section starts swinging. In this state, the contact position of the first part and the second part can be changed. Therefore, the link mechanism can amplify the amount of swing of the load receiving section from when the load receiving section starts swinging. Therefore, the operation sensitivity of the three-point link mechanism is improved compared to a configuration in which the interlocking swing arm does not swing unless the load receiving section swings by a predetermined amount or more. Thus, it is possible to realize a tractor capable of performing control to move a work apparatus upward and downward with high sensitivity according to the tow load.

In the present invention, it is preferable that one of the first part and the second part is a swing member, the other of the first part and the second part is a locking part that is provided with a plurality of recessed portions that are configured to receive and lock the swing member, and the swing member is provided with a positioning mechanism configured to determine a swing angle when the swing member is fitted into any of the plurality of recessed portions.

With this configuration, the combination of the first part and the second part is constituted by the swing member and the locking part, and the swing member fits into a recessed portion of the locking part. Also, when the swing member fits into one of the plurality of recessed portions, the swing angle of the swing member is held by the positioning mechanism. Therefore, the contact position of the first part and the second part is held without being displaced unintentionally. Thus, the interlocking swing arm can more desirably amplify the amount of swing of the load receiving section.

In the present invention, it is preferable that the positioning mechanism is configured to position the swing member at an angle that is orthogonal to a swing angle of the load receiving section.

With this configuration, the angle at which the swing member can be positioned includes an angle that is orthogonal to the swing angle of the load receiving section. That is to say, the swing range of the swing member is set so as to be a range that is close to the angle that is orthogonal to the swing angle of the load receiving section. Therefore, the swing member can reliably receive the reaction force from the locking part. As a result, the swing member can desirably press the locking part. Note that the "orthogonal angle" in the present invention is not limited to a strict orthogonal angle, but may be a substantially orthogonal angle.

In the present invention, it is preferable that a free end portion of the swing member is provided with a pin configured to be fitted into any of the plurality of recessed portions, the locking part is provided with a common recessed portion that includes a plurality of recessed portions so that the plurality of recessed portions are continuously lined up, and the pin is configured to be moved over the common recessed portion and to be fitted into one of the plurality of recessed portions.

With this configuration, a plurality of recessed portions are formed in the common recessed portion, and the pin of the swing member fits into the plurality of recessed portions. Also, the pin is moved over the common recessed portion and is fitted into one of the plurality of recessed portions, and therefore the common recessed portion is formed as gaps between the pin and the plurality of recessed portions. Therefore, it is possible to realize a configuration with which the pin swings between the gaps in the common recessed portion when the operator changes the swing angle of the swing member, and it is further easier to perform the operation to change the swing angle.

In the present invention, it is preferable that the link mechanism is provided with a sensitivity changing section configured to operate so that, as the load receiving section swings toward a side where the tow load is larger, an amount of displacement of a mechanism that is located downstream thereof in the link mechanism increases.

The amount of swing of the load receiving section increases as the tow load applied to the work apparatus increases. It is preferable that, when the tow load applied to the work apparatus increases, the work apparatus is actively controlled so as to move upward in order to reduce the tow load. With this configuration, as the amount of swing of the load receiving section increases, the amount of displacement of a mechanism that is located downstream thereof in the link mechanism increases. As a result, the work apparatus is actively controlled so as to move upward, the tow load is quickly reduced, and damage to the work apparatus and engine stall due to an increase in the tow load can be desirably prevented.

In the present invention, it is preferable that the link mechanism includes, at a position that is downstream of the interlocking swing arm, a link ratio changing section configured to change a rink ratio so that a link ratio change rate is smaller than a link ratio change rate of the first part and the second part.

With this configuration, it is possible to finely adjust the amount of operation for the hydraulic unit.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. Note that the direction indicated by the arrow "F" in <FIG> indicates forward in the travel direction of the tractor, and the direction indicated by the arrow "U" indicates upward of the tractor. In addition, the description "left" and the description "right" in the present specification respectively mean the right and the left when viewed forward in the travel direction of the tractor.

The tractor shown in <FIG> is provided with a pair of left and right front wheels <NUM>, a pair of left and right rear wheels <NUM>, a front frame <NUM>, an intermediate frame <NUM>, a clutch housing <NUM>, a transmission case <NUM>, a driver's part <NUM>, and a pair of left and right rear fenders <NUM>.

The pair of left and right front wheels <NUM> are pivotally supported by the front frame <NUM> provided in a front portion of the vehicle body, and are located at laterally outer positions of the front frame <NUM> with respect to the machine body. The intermediate frame <NUM> is provided rearward of the front frame <NUM>. The clutch housing <NUM> is provided between the front frame <NUM> and the intermediate frame <NUM>, and the front frame <NUM> and the intermediate frame <NUM> are each coupled to the clutch housing <NUM>. The transmission case <NUM> is coupled to a rear end portion of the intermediate frame <NUM>. The clutch housing <NUM> and the transmission case <NUM> are also used as vehicle body frames of the tractor. That is to say, the front frame <NUM>, the intermediate frame <NUM>, the clutch housing <NUM>, and the transmission case <NUM> are provided as vehicle body frames of the tractor.

An engine E is mounted on, and supported by, a rear portion of the front frame <NUM>, and the clutch housing <NUM> is coupled to a lower rear end portion of the engine E. The pair of left and right rear wheels <NUM> are pivotally supported by the transmission case <NUM> so as to be located outside the transmission case <NUM> in a left-right direction.

Although not shown, a main clutch and so on are built into the clutch housing <NUM>. The intermediate frame <NUM> is provided with a transmission shaft. A main transmission device, an auxiliary transmission device, and so on are built into the transmission case <NUM>. The power of the engine E is transmitted to the pair of left and right front wheels <NUM> and the pair of left and right rear wheels <NUM> via the main clutch, the transmission shaft, the main transmission device, the auxiliary transmission device, and so on.

The driver's part <NUM> is provided in a rear portion of the vehicle body, and is configured to allow an operator to ride. The driver's part <NUM> is provided with a steering wheel <NUM> and a driver's seat <NUM>. The operator can sit on the driver's seat <NUM>. The steering wheel <NUM> is provided forward of the driver's seat <NUM>, and the operator steers the pair of left and right front wheels <NUM> by manually operating the steering wheel <NUM>. The rear fenders <NUM> are respectively provided on the left and right sides of the driver's seat <NUM> with respect to the machine body, and the rear fenders <NUM> cover the left and right rear wheels <NUM> from above. The transmission case <NUM> is provided below the driver's seat <NUM>. The driver's seat <NUM> is located between the pair of left and right rear wheels <NUM> in a plan view and in a front-rear view.

A three-point link mechanism <NUM> is coupled to a rear portion of the transmission case <NUM> so as to be able to swing upward and downward, and the three-point link mechanism <NUM> is configured to be capable of attaching a work apparatus <NUM> thereto. The work apparatus <NUM> shown in <FIG> is a plow. Note that the work apparatus <NUM> may be, for example, a rotary tillage device, a disc harrow, a cultivator, a subsoiler, or the like.

The three-point link mechanism <NUM> includes a single top link <NUM>, and left and right lower links <NUM>. The lower links <NUM> are coupled to a lower rear portion of the transmission case <NUM> so as to be able to swing about a swing axis Y1. A load receiving section <NUM> is coupled to an upper rear portion of the transmission case <NUM>, and the top link <NUM> is coupled to the load receiving section <NUM> so as to be able to swing about a swing axis Y2. The load receiving section <NUM> will be described later.

The three-point link mechanism <NUM> is driven by lift arms <NUM> of a hydraulic driven type so as to move upward and downward. Specifically, end portions of link members <NUM> are pivotally coupled to leading end portions of the lift arms <NUM> with pins respectively, and the opposite end portions of the link members <NUM> are pivotally coupled to the lower links <NUM> with pins respectively.

Each lift arm <NUM> is configured to be able to swing upward and downward about a swing axis X, based on the driving of a hydraulic actuator (not shown). The lower links <NUM> swing upward and downward as the lift arms <NUM> swing upward and downward. The top link <NUM> coupled to the work apparatus <NUM> also swings in conjunction with the up-down swing of the lower links <NUM>. The work apparatus <NUM> is coupled to the top link <NUM> and the lower links <NUM> so as to be able to swing relative to the top link <NUM> and the lower links <NUM>. The work apparatus <NUM> moves upward and downward in conjunction with the up-down swing of the top link <NUM> and the lower links <NUM>.

In response to the operator operating a height setting lever <NUM>, the hydraulic oil is supplied to and discharged from the hydraulic actuator, the lift arms <NUM> swing, and the work apparatus <NUM> moves upward and downward. The supply and discharge of hydraulic oil is controlled through the operation of a spool (not shown). A feedback link mechanism (not shown) operates in conjunction with the up-down movement of the work apparatus <NUM>. The feedback link mechanism adjusts the amount of hydraulic oil to be supplied to, or discharged from, the hydraulic actuator, based on the amount of operation of the height setting lever <NUM> and the swing angle of the lift arms <NUM>. When the work apparatus <NUM> reaches a control target height, the supply and discharge of hydraulic oil to and from the hydraulic actuator is stopped, and the up-down swing of the left and right lift arms <NUM> is stopped. In this way, the work apparatus <NUM> is attached to the three-point link mechanism <NUM> so as to be able to move upward and downward. The hydraulic actuator and the spool described in the present embodiment are equivalent to the "hydraulic unit" according to the present invention. That is to say, a hydraulic unit configured to operate to swing the three-point link mechanism <NUM> is provided.

In the present embodiment, the height at which the work apparatus <NUM> works is adjustable based on the work load and the tillage depth when the work apparatus <NUM> performs ground work. For example, if a plow is coupled to the three-point link mechanism <NUM> as the work apparatus <NUM>, the plow receives a reaction force from the ground when ground work with the plow is performed, and this reaction force acts as a tow load. If the tow load is too large, the plow may be damaged or the engine E may stall. Therefore, the tractor according to the present embodiment is provided with a mechanism for moving the work apparatus <NUM> such as a plow upward and downward according to the tow load to adjust the tow load to be constant, i.e., a draft control mechanism. Hereinafter, the draft control mechanism will be described.

As shown in <FIG>, the draft mechanism includes the load receiving section <NUM> and the link mechanism (an interlocking swing arm <NUM>, a coupling link part <NUM>, a tillage depth adjustment cam <NUM>, an interlocking swing part <NUM>, and a linkage rod <NUM>). In order to make the load receiving section <NUM> and the link mechanism as the draft mechanism more visible, <FIG> do not show the lift arms <NUM>, but the swing axis X of the lift arms <NUM> is shown in the drawings.

The load receiving section <NUM> swings according to the tow load from the work apparatus <NUM> when the work apparatus <NUM> performs ground work while being towed by the vehicle body of the tractor. The link mechanism transmits the amount of operation for swinging the three-point link mechanism <NUM>, to the hydraulic unit (including the above-described hydraulic actuator and spool (not shown)) according to the amount of swing of the load receiving section <NUM>. The interlocking swing arm <NUM>, the coupling link part <NUM>, the tillage depth adjustment cam <NUM>, the interlocking swing part <NUM>, and the linkage rod <NUM> are provided as the link mechanism according to the present invention.

The load receiving section <NUM> is provided with a bracket 30A, a receiving member 30B, a fulcrum pin 30C, a linkage pin 30D, a first coil spring 30E, a second coil spring 30F, and a swing prohibiting member <NUM>. The bracket 30A is coupled and fixed to a rear portion of the transmission case <NUM>. The top link <NUM> is coupled to the receiving member 30B.

Round holes capable of inserting the fulcrum pin 30C therethrough are respectively formed in a lower portion of the bracket 30A and a lower portion of the receiving member 30B in a lateral direction with respect to the machine body, and the fulcrum pin 30C penetrates through the round holes in the respective lower portions of the bracket 30A and the receiving member 30B in a lateral direction with respect to the machine body. That is to say, the fulcrum pin 30C pivotally couples the bracket 30A and the receiving member 30B so as to swing about a swing axis P relative to each other, and the receiving member 30B is able to swing forward and rearward about the swing axis P that extends in a lateral direction with respect to the machine body.

A round hole 30o is drilled along a lateral direction with respect to the machine body in a central portion of the receiving member 30B in the vertical direction. In addition, an elongated hole 30p is drilled along a lateral direction with respect to the machine body in a central portion of the bracket 30A in the vertical direction. The lengthwise direction of the elongated hole 30p coincides with the front-rear direction of the machine body. The linkage pin 30D penetrates through the round hole 30o in the central portion of the receiving member 30B in the vertical direction and the elongated hole 30p. The two end portions of the linkage pin 30D in the lengthwise direction thereof are located outside the receiving member 30B. Then, a snap pin is locked to an end portion of the linkage pin 30D in the lengthwise direction thereof, and the linkage pin 30D is prevented from coming loose from the bracket 30A and the receiving member 30B.

The linkage pin 30D cannot be displaced relative to the round hole 30o, and is slidable in the lengthwise direction of the elongated hole 30p. Therefore, the receiving member 30B can swing forward and rearward within the range of the elongated hole 30p in the lengthwise direction thereof.

A housing cylinder <NUM> is formed in an upper portion of the bracket 30A. The housing cylinder <NUM> is formed in a cylindrical shape that extends in the front-rear direction of the machine body. The first coil spring 30E is housed in the housing cylinder <NUM> (see <FIG>). A gap is formed between an upper portion of the bracket 30A and an upper portion of the receiving member 30B. The first coil spring 30E is provided in this gap, and the two ends of the first coil spring 30E in the expanding direction thereof respectively abut against the bracket 30A and the receiving member 30B. The receiving member 30B is biased by the first coil spring 30E so as to swing rearward.

The second coil spring 30F is provided at a position opposite to the first coil spring 30E with respect to the bracket 30A. The elastic modulus of the second coil spring 30F is smaller than the elastic modulus of the first coil spring 30E. When the first coil spring 30E expands and the elastic energy of the first coil spring 30E is released, the second coil spring 30F contracts and the elastic energy of the second coil spring 30F increases. The details will be described later.

Three upper and lower attachment holes <NUM> are formed in a rear portion of the bracket 30A, and one end portion of the top link <NUM> is connected to one of the plurality of attachment holes <NUM> so as to be able to swing upward and downward about a pin. The attachment hole <NUM> coupled to the top link <NUM> of the three upper and lower attachment holes <NUM> serves as the swing axis Y2 of the top link <NUM>.

The end portion of the top link <NUM> opposite to the end portion coupled to the bracket 30A is coupled to an upper portion of the work apparatus <NUM>. Therefore, a tensile force acts from the work apparatus <NUM> to the top link <NUM> in a state where the work apparatus <NUM> is lifted or in a state where the work apparatus <NUM> is not performing ground work. Also, in such a state, a tensile force acts from the top link <NUM> to the receiving member 30B, and the receiving member 30B swings to the rearmost position.

When a plow is coupled to the three-point link mechanism <NUM> as the work apparatus <NUM> and tillage work is performed using the plow, the larger the tillage depth is, the larger the reaction force from the ground that the plow receives is. This reaction force is the tow load, and the upward component of the reaction force acts on the top link <NUM> as a pressing force. This pressing force is transmitted to the receiving member 30B via the top link <NUM>. When this pressing force is larger than the resultant force of the respective elastic forces of the first coil spring 30E and the second coil spring 30F, the receiving member 30B swings forward resisting the resultant force of the respective elastic forces of the first coil spring 30E and the second coil spring 30F.

When the receiving member 30B swings forward, the first coil spring 30E contracts. The elastic force of the first coil spring 30E increases in proportion to the amount of contraction of the first coil spring 30E. Therefore, the forward swing of the receiving member 30B stops at a swing angle at which the pressing force acting on the receiving member 30B due to the tow load of the work apparatus <NUM> and the resultant force of the elastic forces of the first coil spring 30E and the second coil spring 30F are balanced. For this reason, as the tow load caused due to the ground work performed by the work apparatus <NUM> increases, the pressing force acting on the receiving member 30B increases, and the receiving member 30B swings to a more forward position. Thus, the receiving member 30B is configured to be able to detect the tow load of the work apparatus <NUM>.

The swing prohibiting member <NUM> is a member that prohibits the receiving member 30B from swinging. Although not described in detail, the swing prohibiting member <NUM> is configured to be able to swing about a swing axis V (see <FIG>) that extends in the front-rear direction, provided in an upper left portion of the bracket 30A. A handle is provided on an upper portion of the swing prohibiting member <NUM>. A horizontal plate portion that can be interposed in a region between the upper end portion of the bracket 30A and the upper end portion of the receiving member 30B is formed between the swing axis V and the handle. In response to the operator operating the handle to the left and the right, the horizontal plate portion swings upward and downward. In a state where the receiving member 30B has swung to the rearmost position, if the swing prohibiting member <NUM> swings in the clockwise direction shown in <FIG>, the horizontal plate portion is interposed so as to fill the entire gap between the upper end portion of the bracket 30A and the upper end portion of the receiving member 30B, and restricts the receiving member 30B from swinging forward. As a result, the receiving member 30B is not able to swing. If the swing prohibiting member <NUM> swings in the counterclockwise direction shown in <FIG>, the horizontal plate portion is separated from the region between the upper end portion of the bracket 30A and the upper end portion of the receiving member 30B so that the receiving member 30B is able to swing forward and rearward.

The load receiving section <NUM> is provided with an amplification adjustment section <NUM>. In addition, the interlocking swing arm <NUM> is pivotally coupled to the bracket 30A with a pin so as to be able to swing forward and rearward. The interlocking swing arm <NUM> is provided at the most upstream position in the link mechanism. The interlocking swing arm <NUM> is coupled to a right side portion of the bracket 30A so as to be able to swing forward and rearward about a swing axis Q1 that extends in a lateral direction with respect to the machine body. The amplification adjustment section <NUM> is fixed to a right side portion of the receiving member 30B with a bolt. The interlocking swing arm <NUM> swings about the swing axis Q1 that is different from the swing axis P of the load receiving section <NUM>, in conjunction with the swing of the load receiving section <NUM>.

The amplification adjustment section <NUM> swings integrally with the receiving member 30B, and when the receiving member 30B swings forward, the interlocking swing arm <NUM> and the amplification adjustment section <NUM> abut against each other, and the interlocking swing arm <NUM> swings. The interlocking swing arm <NUM> is configured to be able to amplify the amount of swing of the receiving member 30B by swinging by a larger degree than the front-rear swing of the receiving member 30B. The details will be described later. In addition, the amplification adjustment section <NUM> is configured to be able to adjust the amount of swing of the interlocking swing arm <NUM>. The details will be described later.

An abutting bolt <NUM> is coupled to an upper front portion of the receiving member 30B with respect to the amplification adjustment section <NUM>. In a state where the receiving member 30B has swung to the rearmost position, the abutting bolt <NUM> and the interlocking swing arm <NUM> abut against each other, and the interlocking swing arm <NUM> and the amplification adjustment section <NUM> are separated from each other. In response to the receiving member 30B swinging forward, the interlocking swing arm <NUM> swings about the swing axis Q1 while the abutting bolt <NUM> and the interlocking swing arm <NUM> abut against each other. At this time, the more the receiving member 30B swings forward, the smaller the separation distance between the interlocking swing arm <NUM> and the amplification adjustment section <NUM> is. Thereafter, when the receiving member 30B swings further forward and the interlocking swing arm <NUM> and the amplification adjustment section <NUM> abut against each other, the abutting bolt <NUM> and the interlocking swing arm <NUM> are separated from each other.

As described above, the lift arms <NUM> (see <FIG>, hereinafter the same applies) swings upward and downward due to hydraulic oil being supplied to or discharged from the hydraulic actuator, and the supply and discharge of hydraulic oil is controlled through the operation of a spool (not shown). The coupling link part <NUM>, the tillage depth adjustment cam <NUM>, the interlocking swing part <NUM>, and the linkage rod <NUM> are included in the link mechanism for transmitting the swing operation of the receiving member 30B to the spool.

As shown in <FIG>, one end portion of the coupling link part <NUM> is pivotally coupled to a lower end portion of the interlocking swing arm <NUM> with a pin member <NUM> so as to be able to swing relative to the swing arm <NUM>, and the tillage depth adjustment cam <NUM> is pivotally coupled to the other end portion of the coupling link part <NUM> with a pin so as to be able to swing relative to the coupling link part <NUM>. A support member <NUM> is coupled to a right side portion of the transmission case <NUM>, and two cylinder members 37A and 37B protrude from the support member <NUM> in lateral directions with respect to the machine body. The tillage depth adjustment cam <NUM> is supported by the cylinder member 37B so as to be able to swing forward and rearward about a swing axis Z1 that extends in a lateral direction with respect to the machine body.

As shown in <FIG>, the coupling link part <NUM> includes a first link member 32A, a second link member 32B, a coil spring member 32C, and a conjunction pin 32D. The first link member 32A is formed by welding a flat plate member and a bolt member to each other. End portions of the flat plate member and the bolt member in the lengthwise direction thereof are coupled to each other by welding. The end portion of the flat plate member of the first link member 32A opposite to the end portion welded to the bolt member is pivotally coupled to the second link member 32B with the conjunction pin 32D so as to be able to swing relative to the second link member 32B. The second link member 32B is a flat plate member. The end portion of the second link member 32B opposite to the end portion pivotally coupled to the first link member 32Ais pivotally coupled to the tillage depth adjustment cam <NUM> so as to be able to swing relative to the tillage depth adjustment cam <NUM>.

A pair of nuts are locked to upper and lower end regions of the bolt member of the first link member 32A, and the coil spring member 32C and the pin member <NUM> are fitted onto the region between the pair of nuts. The coil spring member 32C is provided upward of the pin member <NUM>, i.e., on the second link member 32B side. The pin member <NUM> is fitted onto the bolt member of the first link member 32A, and is inserted through one of a plurality of insertion holes <NUM> formed in a lower end portion of the interlocking swing arm <NUM>, and is fastened with a snap pin so as not to come loose from the insertion hole <NUM>. That is to say, the lower end portion of the bolt member of the first link member 32A and the lower end portion of the interlocking swing arm <NUM> are coupled to each other with the pin member <NUM> so as to be able to swing.

One end portion of a tension spring <NUM> is hooked on the tillage depth adjustment cam <NUM>, and the other end portion of the tension spring <NUM> is hooked on a hook member <NUM>. The hook member <NUM> is supported by the cylinder member 37A. The cylinder member 37A is located forward of the tillage depth adjustment cam <NUM> with respect to the machine body, and the tension spring <NUM> tensions the tillage depth adjustment cam <NUM> and the cylinder member 37A. Therefore, the tillage depth adjustment cam <NUM> is biased so as to swing forward. Note that a lower end portion of a swing arm 23A of the height setting lever <NUM> and a lower end portion of a swing arm 24A of a tillage lever <NUM> are fitted onto the cylinder member 37A. The lengthwise direction of the cylinder member 37A extends along a swing axis Y3 that extends in a lateral direction with respect to the machine body. The lower end portion of the swing arm 23A and the lower end portion of the swing arm 24A are swing base end portions. That is to say, the height setting lever <NUM> and the tillage lever <NUM> is able to swing forward and rearward about the swing axis Y3.

The tillage depth adjustment cam <NUM> is provided with a cam portion 34a. A roller 35A is provided in a central region of the interlocking swing part <NUM> in the lengthwise direction thereof, and the cam portion 34a and the roller 35A is able to abut against each other. The cam portion 34a is inclined so as to be separated from the swing axis Z1 in a forward direction. Therefore, when a front region of the cam portion 34a and the roller 35A abut against each other, the degree of swing of the interlocking swing part <NUM> is higher than when a rear region of the cam portion 34a and the roller 35A abut against each other. The tillage depth adjustment cam <NUM> is equivalent to the "sensitivity changing section" according to the present invention.

As shown in <FIG> and <FIG>, in response to the tillage depth adjustment cam <NUM> swinging rearward about the swing axis Z1 and the cam portion 34a and the roller 35A abutting against each other, the interlocking swing part <NUM> swings rearward while the roller 35A moves along the cam portion 34a. In response to the interlocking swing part <NUM> swinging rearward, the cam portion 34a and the roller 35A abut against each other on a front region of the cam portion 34a. Therefore, the amount of change in the swing angle of the interlocking swing part <NUM> becomes large relative to the amount of change in the swing angle of the tillage depth adjustment cam <NUM>. That is to say, the tillage depth adjustment cam <NUM>, which serves as the sensitivity changing section, operates so that, as the load receiving section <NUM> swings to the side where tow load is larger, the amount of displacement of the mechanism that is located downstream thereof in the link mechanism increases.

The tillage depth adjustment cam <NUM> is provided with a coupling portion 34b for a control cable of a rotary tillage device, and one end portion of a control cable can be coupled to the coupling portion 34b. The control cable of the rotary tillage device is described in FIGS. <NUM> and <NUM> of <CIT>. The coupling portion 34b is located on the opposite side of the cam portion 34a with respect to the interlocking swing part <NUM>. In automatic tillage depth control that is performed by the rotary, the coupling portion 34b is pulled via the control cable when a grounding body provided in the rotary tillage device swings upward and downward, and accordingly the tillage depth adjustment cam <NUM> swings forward and rearward. If a control cable is coupled to the coupling portion 34b, generally, the swing prohibiting member <NUM> is operated so as to swing downward, and the receiving member 30B is restricted from swinging forward. In this case, as shown in <FIG>, the first link member 32A and the second link member 32B are configured to be flexible with the conjunction pin 32D being interposed therebetween, and therefore the tillage depth adjustment cam <NUM> is able to swing even when the receiving member 30B is not able to swing.

A plurality of insertion holes <NUM> are formed in a free end portion of the interlocking swing part <NUM>, and a rear end portion of the linkage rod <NUM> is pivotally coupled to one of the plurality of insertion holes <NUM> with a pin. In response to the interlocking swing part <NUM> swinging rearward, the linkage rod <NUM> is displaced rearward. Although not shown in the drawings, the link mechanism that operates the spool for adjusting the supply/discharge amount of hydraulic oil is coupled to a front end portion of the linkage rod <NUM>. In response to the linkage rod <NUM> being displaced rearward, the spool is operated and hydraulic oil is supplied to the hydraulic actuator, and the lift arms <NUM> swings upward.

The swing base end portion of the interlocking swing part <NUM> is pivotally coupled to a free end portion of a bracket 24B with a pin, so as to be able to swing, and the interlocking swing part <NUM> is able to swing forward and rearward about a swing axis Z2. At the position where the cylinder member 37A is located, the respective swing base end portions of the swing arm 24A and the bracket 24B are coupled to each other by welding. Also, the tillage depth adjustment cam <NUM> is able to abut against the swing arm 24A. In response to the tillage depth adjustment cam <NUM> swinging rearward, the cam portion 34a and the roller 35A approach each other, and it becomes easier for the interlocking swing part <NUM> to be operated so as to swing rearward. That is to say, in response to the tillage depth adjustment cam <NUM> being swung rearward, it becomes easier for the lift arms <NUM> to be operated so as to swing upward.

A torsion spring <NUM> is wound around a swinging portion of the interlocking swing part <NUM>. The torsion spring <NUM> is locked to a downward portion of the swing base end portion of the interlocking swing part <NUM> and a downward portion of the free end portion of the bracket 24B. The interlocking swing part <NUM> is biased by the torsion spring <NUM> so as to swing forward.

In response to the receiving member 30B swinging forward by receiving a pressing force from the work apparatus <NUM>, the interlocking swing arm <NUM> abuts against the abutting bolt <NUM> or the amplification adjustment section <NUM>, and the interlocking swing arm <NUM> swings clockwise in the side view in <FIG> and <FIG>. The coupling link part <NUM> is pulled rearward in conjunction with the swing of the interlocking swing arm <NUM>. At this time, as shown in <FIG>, the first link member 32A and the second link member 32B are pulled and extend straight, and therefore a tensile force is applied from the coupling link part <NUM> to the tillage depth adjustment cam <NUM>. Thus, the coupling link part <NUM> is displaced rearward, and the tillage depth adjustment cam <NUM> swings rearward.

As the tillage depth adjustment cam <NUM> swings, the cam portion 34a and the roller 35A approach each other. When the cam portion 34a and the roller 35A abut against each other, the interlocking swing part <NUM> swings rearward while the roller 35A moves along the cam portion 34a. The linkage rod <NUM> coupled to the interlocking swing part <NUM> so as to be able to swing is pulled, and is displaced rearward. The above-described spool is moved so that hydraulic oil is supplied to the hydraulic actuator, the lift arms <NUM> swings upward in conjunction with the swing of the interlocking swing part <NUM>, and the work apparatus <NUM> moves upward.

If the work apparatus <NUM> is a plow, the reaction force applied from the ground to the plow decreases as the position of the plow moves upward, and thus the pressing force acting from the plow to the receiving member 30B via the top link <NUM> also decreases. Thereafter, when the pressing force acting on the receiving member 30B and the elastic force of the first coil spring 30E are balanced, the swing of the receiving member 30B, the interlocking swing arm <NUM>, the tillage depth adjustment cam <NUM>, and the interlocking swing part <NUM> is stopped, and the linkage rod <NUM> is no longer displaced. Thereafter, the supply and discharge of hydraulic oil to and from the hydraulic actuator is stopped by the above-described feedback link mechanism operating the spool, and the up-down swing of the left and right lift arms <NUM> is stopped.

When the pressing force does not act on the receiving member 30B, the receiving member 30B stands still at the rearmost end of the front-rear swing range that is based on the front-rear length of the elongated hole 30p. At this time, the first link member 32A and the second link member 32B in the coupling link part <NUM> are loose, and therefore, even if the interlocking swing arm <NUM> swings, the tillage depth adjustment cam <NUM> does not move in conjunction with the swing of the interlocking swing arm <NUM>. In addition, the coil spring member 32C is fitted onto the first link member 32A in the coupling link part <NUM>. As a result, even if the receiving member 30B that has swung forward swings abruptly to the rearmost end position and the interlocking swing arm <NUM> also swings abruptly, the impact caused by such an abrupt swing is absorbed by the expansion and contraction operation of the coil spring member 32C. Therefore, it is possible to avoid the problem in that the tillage depth adjustment cam <NUM> and the interlocking swing part <NUM> unnecessarily swing due to the impact. At this time, the tillage depth adjustment cam <NUM> swings forward due to the elastic force of the tension spring <NUM>. Also, the interlocking swing part <NUM> swings forward due to the elastic force of the torsion spring <NUM>.

As described above, the interlocking swing arm <NUM> is configured to be able to amplify the amount of swing of the receiving member 30B. The amplification adjustment section <NUM> is fixed to the receiving member 30B with a bolt, and the amplification adjustment section <NUM> and the interlocking swing arm <NUM> are configured to be able to abut against each other.

The interlocking swing arm <NUM> extends in the top-bottom direction. If the abutting point of the amplification adjustment section <NUM> and the interlocking swing arm <NUM> is changed in the top-bottom direction, the amount of swing of the interlocking swing arm <NUM> changes even if the amount of swing of the receiving member 30B is the same. The amplification adjustment section <NUM> is configured to be able to adjust the abutting point against the interlocking swing arm <NUM> in the top-bottom direction.

As shown in <FIG>, the amplification adjustment section <NUM> is provided with a bracket member <NUM> and a swing member <NUM>. Elongated holes 50a are formed in an upper end portion and a lower end portion of a flat surface portion of the bracket member <NUM>, and the pair of upper and lower elongated holes 50a extend in a top-bottom direction. Bolts are inserted into the pair of upper and lower elongated holes 50a. That is to say, the bracket member <NUM> is coupled to the receiving member 30B with a bolt so as to be able to adjust the position thereof in the top-bottom direction. A protruding cylinder portion 50b is formed on a region between the pair of upper and lower elongated holes 50a, and the protruding cylinder portion 50b protrudes to the side opposite to the side where the receiving member 30B is located. A thread groove engageable with a nut is formed in a protruding leading end portion of the protruding cylinder portion 50b.

The swing member <NUM> is configured to be able to swing relative to the bracket member <NUM>. A bolt insertion hole 51b is formed in a swing base end portion of the swing member <NUM>. The protruding cylinder portion 50b is inserted into the bolt insertion hole 51b, and a nut engages with the leading end portion of the protruding cylinder portion 50b. Thus, the swing member <NUM> is configured to be able to swing upward and downward about a swing axis Q2. The swing member <NUM> is equivalent to the "first part" according to the present invention. That is to say, the load receiving section <NUM> is provided with the swing member <NUM> that serves as the first part that presses the interlocking swing arm <NUM>.

A free end portion of the swing member <NUM> is provided with a fitting pin 51a. The fitting pin 51a is formed in a cylindrical shape that extends in a lateral direction with respect to the machine body. The fitting pin 51a may be welded and fixed to the free end portion of the swing member <NUM>, or coupled to the free end portion of the swing member <NUM> with a bolt. The fitting pin 51a is equivalent to the "pin" according to the present invention.

The interlocking swing arm <NUM> is provided with the "second part" that comes into contact with the swing member <NUM> serving as the first part, and is pressed by the swing member <NUM>. In the present embodiment, the second part is a locking part <NUM>. The locking part <NUM> is provided with a plurality of recessed portions that can receive and lock the swing member <NUM>. As the "plurality of recessed portions", a first recessed portion 52a, a second recessed portion 52b, and a third recessed portion 52c are provided in a portion that is upward of the swing axis Q1, of the interlocking swing arm <NUM>, so as to be lined up in a top-bottom direction.

Among the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c, the first recessed portion 52a is the farthest from the swing axis Q1 and the third recessed portion 52c is the closest to the swing axis Q1. The first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c are each formed so as to be curved in an arc shape in correspondence with the cylindrical fitting pin 51a. Thus, the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c are each configured to be able to receive and lock the fitting pin 51a. That is to say, the fitting pin 51a can be fitted into the first recessed portion 52a, the second recessed portion 52b, or the third recessed portion 52c.

A portion that is upward of the first recessed portion 52a and a portion that is downward of the third recessed portion 52c, of the interlocking swing arm <NUM>, are respectively provided with a pair of upper and lower protruding portions 52d and 52e, and the pair of upper and lower protruding portions 52d and 52e protrude toward the swing member <NUM> more than the other portions of the interlocking swing arm <NUM>. The fitting pin 51a is positioned between the pair of upper and lower protruding portions 52d and 52e, and the fitting pin 51a is able to swing about the swing axis Q2 within the top-bottom range between the pair of upper and lower protruding portions 52d and 52e. The first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c are provided between the pair of upper and lower protruding portions 52d and 52e so as to be lined up in a top-bottom direction. The region surrounded by the pair of upper and lower protruding portions 52d and 52e, the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c like a cove is equivalent to the "common recessed portion" according to the present invention. That is to say, the locking part <NUM> is provided with a common recessed portion that includes a plurality of recessed portions so that the plurality of recessed portions are continuously lined up. The fitting pin 51a is moved over the common recessed portion and is fitted into one of the plurality of recessed portions.

The swing member <NUM> is configured to be able to switch between a state in which the fitting pin 51a and the first recessed portion 52a are able to engage with each other, a state in which the fitting pin 51a and the second recessed portion 52b are able to engage with each other, and a state in which the fitting pin 51a and the third recessed portion 52c are able to engage with each other, by swinging upward and downward. In this way, a configuration is employed so that the contact point of the swing member <NUM> serving as the first part and the locking part <NUM> serving as the second part can be changed.

The swing member <NUM> is provided with a "positioning mechanism" that determines the swing angle when the swing member <NUM> is fitted into one of the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c. The positioning mechanism according to the present embodiment is a detent mechanism. The positioning mechanism is provided with a ball 51o, a coil spring member 51p, and detent recessed portions 50p, 50q, and 50r.

A handle arm 51c is coupled to a portion that is adjacent to the fitting pin 51a on the bolt insertion hole 51b side, of the swing member <NUM>. The handle arm 51c protrudes to the side opposite to the side where the receiving member 30B is located. A handle 51d is coupled rearward to a protruding leading end portion of the handle arm 51c.

The handle arm 51c is formed in a cylindrical shape. As shown in <FIG>, a cylindrical hole is formed in the handle arm 51c in the lengthwise direction of the handle arm 51c, and the ball 51o and the coil spring member 51p for the detent mechanism are inserted into this cylindrical hole. As shown in <FIG> and <FIG>, the detent recessed portions 50p, 50q, and 50r are formed in three portions of the bracket member <NUM>, the three portions being along the swing trajectory of the handle arm 51c. The ball 51o for the detent mechanism engages with one of the detent recessed portions 50p, 50q, and 50r. If the ball 51o engages with the detent recessed portion 50p, the fitting pin 51a and the first recessed portion 52a are able to engage with each other. If the ball 51o engages with the detent recessed portion 50q, the fitting pin 51a and the second recessed portion 52b are able to engage with each other. If the ball 51o engages with the detent recessed portion 50r, the fitting pin 51a and the third recessed portion 52c are able to engage with each other. In this way, the swing member <NUM> is configured to be able to swing upward and downward according to three levels.

The positioning mechanism according to the present embodiment is able to position the swing member <NUM> at an angle that is orthogonal to the swing angle of the load receiving section <NUM>. If the ball 51o engages with the detent recessed portion 50q, the straight line passing through the swing axis P and the swing axis Q2 and the straight line passing through the center point of the fitting pin 51a in the side view of the machine body and the swing axis Q2 are orthogonal or substantially orthogonal to each other (see <FIG>). That is to say, the angle at which the swing member <NUM> is positioned (the swing angle of the swing member <NUM> positioned by the positioning mechanism) includes an angle that is orthogonal to the swing angle of the load receiving section <NUM>. The detent recessed portion 50p and the detent recessed portion 50r are located upward and downward of the detent recessed portion 50q, respectively. Therefore, the swing member <NUM> is able to reliably receive the reaction force from the locking part <NUM>.

When the pressing force does not act on the receiving member 30B, the receiving member 30B comes to rest at the rearmost end of the front-rear swing range that is based on the front-rear length of the elongated hole 30p. At this time, the interlocking swing arm <NUM> abuts against the abutting bolt <NUM> of the receiving member 30B, and is separated from the swing member <NUM>. Therefore, when the pressing force does not act on the receiving member 30B, the operator can easily perform an operation to switch the swing member <NUM> to the above-described three levels.

As described above, in response to the receiving member 30B swinging forward, at first, the interlocking swing arm <NUM> swings due to the abutting bolt <NUM> and the interlocking swing arm <NUM> abutting against each other. The receiving member 30B swings about the swing axis P, and the interlocking swing arm <NUM> swings about the swing axis Q1. The separation distance between the swing member <NUM> and the swing axis P is longer than the separation distances between the swing axis Q1 and each of the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c. Therefore, when the receiving member 30B swings forward in the state where the abutting bolt <NUM> and the interlocking swing arm <NUM> abut against each other, the amounts of displacement of the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c are smaller than the amount of displacement of the swing member <NUM>. Therefore, in response to the receiving member 30B swinging forward in a state where the abutting bolt <NUM> and the interlocking swing arm <NUM> abut against each other, the fitting pin 51a approaches the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c. Thereafter, when the fitting pin 51a abuts against one of the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c, the abutting bolt <NUM> and the interlocking swing arm <NUM> separate from each other.

As shown in <FIG>, if the abutting point of the swing member <NUM> and the interlocking swing arm <NUM> is set to a different point from among the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c, the amount of swing of the interlocking swing arm <NUM> varies even if the amount of swing of the receiving member 30B is the same. <FIG> shows an abutting state of the fitting pin 51a and the first recessed portion 52a. <FIG> shows an abutting state of the fitting pin 51a and the second recessed portion 52b. <FIG> shows an abutting state of the fitting pin 51a and the third recessed portion 52c. In any of <FIG>, the swing prohibiting member <NUM> has been operated so as to be in a state where the swing prohibiting member <NUM> does not restrict the receiving member 30B from swinging.

The second recessed portion 52b is closer to the swing axis Q1 than the first recessed portion 52a is. Therefore, as shown in <FIG>, the amount of swing (indicated by D2) of the interlocking swing arm <NUM> when the fitting pin 51a and the second recessed portion 52b abut against each other is larger than the amount of swing (indicated by D1) of the interlocking swing arm <NUM> when the fitting pin 51a and the first recessed portion 52a abut against each other. Therefore, when the fitting pin 51a and the second recessed portion 52b abut against each other, the top link <NUM> swings upward and downward by a larger degree than when the fitting pin 51a and the first recessed portion 52a abut against each other.

The third recessed portion 52c is closer to the swing axis Q1 than the second recessed portion 52b is. Therefore, as shown in <FIG>, the amount of swing (indicated by D3) of the interlocking swing arm <NUM> when the fitting pin 51a and the third recessed portion 52c abut against each other is larger than the amount of swing (indicated by D2) of the interlocking swing arm <NUM> when the fitting pin 51a and the second recessed portion 52b abut against each other. Therefore, when the fitting pin 51a and the third recessed portion 52c abut against each other, the top link <NUM> swings upward and downward by a larger degree than when the fitting pin 51a and the second recessed portion 52b abut against each other. In this way, the more the front-rear swing of the receiving member 30B is amplified, the larger the degree by which the lift arms <NUM> swings upward and downward is.

Also, the angular velocity and the angular acceleration of the interlocking swing arm <NUM> when swinging also change in proportion to the change in the amount of swing of the interlocking swing arm <NUM>. That is to say, the angular velocity and angular acceleration of the interlocking swing arm <NUM> when the fitting pin 51a and the second recessed portion 52b abut against each other are higher than the angular velocity and angular acceleration of the interlocking swing arm <NUM> when the fitting pin 51a and the first recessed portion 52a abut against each other. Also, the angular velocity and angular acceleration of the interlocking swing arm <NUM> when the fitting pin 51a and the third recessed portion 52c abut against each other are higher than the angular velocity and angular acceleration of the interlocking swing arm <NUM> when the fitting pin 51a and the second recessed portion 52b abut against each other. The higher the angular velocity and angular acceleration of the interlocking swing arm <NUM> are, the higher the angular velocity and angular acceleration of the tillage depth adjustment cam <NUM> and the interlocking swing part <NUM> when swinging. As the angular velocity and angular acceleration of the interlocking swing part <NUM> increase, the velocity and acceleration of the linkage rod <NUM> when being displaced increase as well, so that the spool for controlling the supply and discharge of hydraulic oil is also operated at high speed. If the spool is operated at high speed, the operation of the hydraulic actuator for the lift arms <NUM> becomes agile, so that the responsiveness of the lift arms <NUM> increases and the angular velocity of the lift arms <NUM> when swinging increases. That is to say, the more the front-rear swing of the receiving member 30B is amplified by the interlocking swing arm <NUM>, the higher the angular velocity and angular acceleration of the lift arms <NUM> when swinging are.

In this way, the link ratio between the receiving member 30B and the interlocking swing arm <NUM> can be changed by changing the abutting point of the swing member <NUM> and the locking part <NUM>. Also, in the present embodiment, four insertion holes <NUM> are formed in the lower end portion of the interlocking swing arm <NUM>, and three insertion holes <NUM> are formed in the free end portion of the interlocking swing part <NUM>. The insertion holes <NUM> are equivalent to the "link ratio changing section" according to the present invention. The insertion holes <NUM> are equivalent to the "link ratio changing section" according to the present invention as well.

One of the four insertion holes <NUM> is selected, and the pin member <NUM> is inserted into this insertion hole <NUM>. If a different insertion hole <NUM> is selected, the amount of displacement of the coupling link part <NUM> changes. A lower insertion hole <NUM> displaces the coupling link part <NUM> by a larger amount. That is to say, the link ratio between the interlocking swing arm <NUM> and the coupling link part <NUM> is configured to be changeable by the insertion holes <NUM> at four positions. Here, the rate of change in the link ratio between the receiving member 30B and the interlocking swing arm <NUM> when the abutting point of the swing member <NUM> and the locking part <NUM> is changed to the upper and lower adjacent points in response to the operator performing an operation to switching the swing member <NUM> is defined as a first link ratio change rate. The rate of change in the link ratio between the interlocking swing arm <NUM> and the coupling link part <NUM> when the insertion hole, of the four insertion holes <NUM>, for connection with the coupling link part <NUM> is changed to the adjacent insertion hole <NUM> is defined as a second link ratio change rate. The second link ratio change rate is smaller than the first link ratio change rate.

One of the three insertion holes <NUM> are selected, and a rear end portion of the linkage rod <NUM> is pivotally coupled to this insertion hole <NUM> with a pin. If a different insertion hole <NUM> is selected, the amount of displacement of the linkage rod <NUM> changes. An insertion hole <NUM> closer to the free end portion displaces the linkage rod <NUM> by a larger amount. That is to say, the link ratio between the interlocking swing part <NUM> and the linkage rod <NUM> is configured to be changeable by the insertion holes <NUM> at three positions. Here, the rate of change in the link ratio between the interlocking swing part <NUM> and the linkage rod <NUM> when the insertion hole, of the three insertion holes <NUM>, for connection with the linkage rod <NUM> is changed to the adjacent insertion hole <NUM> is defined as a third link ratio change rate. The third link ratio change rate is smaller than the above-described first link ratio change rate.

That is to say, the insertion holes <NUM> and <NUM> are provided downstream of the interlocking swing arm <NUM> in the link mechanism, as a link ratio changing section that changes the link ratio to a link ratio change rate that is smaller than the link ratio change rate of the swing member <NUM> and the locking part <NUM>.

As shown in <FIG>, the second coil spring 30F is provided on the side opposite to the side where the first coil spring 30E is located, with respect to the bracket 30A. The following describes a structure for attaching the second coil spring 30F.

The housing cylinder <NUM> is formed in an upper portion of the bracket 30A, and the first coil spring 30E is housed in the housing cylinder <NUM>. A through hole 30q that extends in a front-rear direction is formed in a central portion of a front portion of the housing cylinder <NUM> in radial direction. In addition, a hollow boss member <NUM> is coupled to a front portion of the housing cylinder <NUM>. A thread groove is formed on the outer circumferential surface of a front portion of the boss member <NUM>, and a nut <NUM> engages with this thread groove. Note that a spacer is provided between a rear end portion of the boss member <NUM> and the nut <NUM>, and this spacer may be composed of a plurality of washers (flat washers or spring washers). The nut <NUM> protrudes to a position that is forward of the bracket 30A, and the position of the nut <NUM> is adjusted by the spacer. That is to say, the position of the nut <NUM> in a front-rear direction may be adjustable according to the length of the second coil spring 30F. Note that the nut <NUM> and the spacer may be an integrated piece, or the nut <NUM> may be a double nut, with no spacer being provided. Also, the boss member <NUM> and the nut <NUM> may be integrally formed as one member, or the outer circumferential surface of the front portion of the boss member <NUM> may be configured without a screw groove.

A protrusion 30t that protrudes forward is welded and fixed to a region of the receiving member 30B where the first coil spring 30E abuts, and a rod <NUM> is pivotally coupled to the protrusion 30t so as to be able to swing upward and downward. The rod <NUM> penetrates through the space inside the inner periphery of the first coil spring 30E. The rod <NUM> penetrates through the hollow hole of the boss member <NUM> fitted into the through hole 30q, and a protruding leading end portion of the rod <NUM> protrudes to a position that is forward of the bracket 30A.

The second coil spring 30F is fitted onto the rod <NUM> at a position forward of the bracket 30A with respect to the machine body. A flat washer <NUM> that has a diameter larger than the outer diameter of the second coil spring 30F is fitted onto an end portion of the rod <NUM> on the side opposite to the side where the receiving member 30B is located.

A thread groove is formed in a protruding leading end portion of the rod <NUM>. Both sides of the flat washer <NUM> are fastened with nuts, and the flat washer <NUM> is sandwiched between the pair of nuts. The position of the flat washer <NUM> in a front-rear direction may be adjustable according to the length of the second coil spring 30F. Also, the nut <NUM> is formed so as to have an opposite side diameter larger than the outer diameter of the second coil spring 30F. That is to say, the two end portions of the second coil spring 30F in the extending direction respectively abut against the nut <NUM> and the flat washer <NUM>. Also, the thread groove of the boss member <NUM> and the nuts sandwiching the flat washer <NUM> are formed so as to have an outer diameter that is slightly smaller than the inner diameter of the second coil spring 30F. Therefore, the thread groove of the boss member <NUM> and the nuts sandwiching the flat washer <NUM> abut against the inner circumferential surface of the second coil spring 30F without rattling.

As the receiving member 30B swings forward and rearward, the rod <NUM> is displaced forward and rearward while swinging relative to the receiving member 30B. At this time, as the receiving member 30B swings, the rod <NUM> is displaced in a top-bottom direction. Therefore, it is necessary to prevent the rod <NUM> and the inner circumferential surface of the hollow hole of the boss member <NUM> from interfering with each other. Therefore, the hollow hole of the boss member <NUM> is formed as to have a diameter that is sufficiently larger than the cross-sectional diameter of the rod <NUM>.

In response to the receiving member 30B swinging forward and rearward, the separation distance between the bracket 30A and the receiving member 30B changes, and the separation distance between the nut <NUM> supported by the bracket 30A and the flat washer <NUM> supported by the receiving member 30B with the rod <NUM> being interposed therebetween changes as well. As a result, the first coil spring 30E expands and contracts. Also, in response to the receiving member 30B swinging forward and rearward, the rod <NUM> is displaced forward and rearward, the separation distance between the nut <NUM> and the flat washer <NUM> changes, and the second coil spring 30F expands and contracts.

As the first coil spring 30E expands and the elastic energy of the first coil spring 30E decreases, the second coil spring 30F contracts and the elastic energy of the second coil spring 30F increases. If the pressing force suddenly stops acting on the receiving member 30B, the elastic energy of the first coil spring 30E is released at once. Therefore, it is conceivable that the receiving member 30B swings abruptly from the state in which the receiving member 30B has swung forward, to the rearmost end of the front-rear swing range thereof that is based on the length of the elongated hole 30p in the front-rear direction. Even in such a case, the second coil spring 30F contracts as the receiving member 30B swings rearward, and the second coil spring 30F stores the elastic energy. Thus, the first coil spring 30E is prevented from abruptly expanding. As a result, the impact when the linkage pin 30D abuts against the rearmost end of the elongated hole 30p is alleviated. In addition, the receiving member 30B is prevented from chattering due to such abutting.

The present invention is not limited to the configuration illustrated in the above-described embodiment, and the following illustrates other typical embodiments of the present invention.

It should be noted that the configurations disclosed in the above-described embodiments (including the other embodiments, the same applies hereinafter) can be applied in combination with the configurations disclosed in other embodiments as long as no contradiction arises. In addition, the embodiments disclosed in the present description are examples. Embodiments of the present invention is not limited to these embodiments, and can be appropriately modified without departing from the object of the present invention.

Claim 1:
A tractor comprising:
a three-point link mechanism (<NUM>) that is coupled to a rear portion of a vehicle body so as to be able to swing upward and downward, and to which a work apparatus (<NUM>) is to be attached so as to be able to move upward and downward;
a hydraulic unit (<NUM>) configured to perform a swing operation to swing the three-point link mechanism;
a load receiving section (<NUM>) configured to swing in response to a tow load being applied from the work apparatus when the work apparatus performs ground work while being towed by the vehicle body; and
a link mechanism (<NUM>,<NUM>,<NUM>,<NUM>,<NUM>) configured to transmit an amount of operation for the swing operation to the hydraulic unit according to an amount of swing of the load receiving section,
wherein the link mechanism includes, at a most upstream position, an interlocking swing arm (<NUM>) configured to swing in conjunction with the swing of the load receiving section about a swing axis that is different from a swing axis of the load receiving section,
the load receiving section (<NUM>) is provided with a first part (<NUM>) configured to press the interlocking swing arm,
the interlocking swing arm is provided with a second part (<NUM>) configured to come into contact with the first part so as to be pressed by the first part, and
a contact position of the first part (<NUM>) and the second part (<NUM>) is changeable.